rust_binder: add Rust Binder driver

We're generally not proponents of rewrites (nasty uncomfortable things
that make you late for dinner!). So why rewrite Binder?

Binder has been evolving over the past 15+ years to meet the evolving
needs of Android. Its responsibilities, expectations, and complexity
have grown considerably during that time. While we expect Binder to
continue to evolve along with Android, there are a number of factors
that currently constrain our ability to develop/maintain it. Briefly
those are:

1. Complexity: Binder is at the intersection of everything in Android and
   fulfills many responsibilities beyond IPC. It has become many things
   to many people, and due to its many features and their interactions
   with each other, its complexity is quite high. In just 6kLOC it must
   deliver transactions to the right threads. It must correctly parse
   and translate the contents of transactions, which can contain several
   objects of different types (e.g., pointers, fds) that can interact
   with each other. It controls the size of thread pools in userspace,
   and ensures that transactions are assigned to threads in ways that
   avoid deadlocks where the threadpool has run out of threads. It must
   track refcounts of objects that are shared by several processes by
   forwarding refcount changes between the processes correctly.  It must
   handle numerous error scenarios and it combines/nests 13 different
   locks, 7 reference counters, and atomic variables. Finally, It must
   do all of this as fast and efficiently as possible. Minor performance
   regressions can cause a noticeably degraded user experience.

2. Things to improve: Thousand-line functions [1], error-prone error
   handling [2], and confusing structure can occur as a code base grows
   organically. After more than a decade of development, this codebase
   could use an overhaul.

[1]: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/drivers/android/binder.c?h=v6.5#n2896
[2]: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/drivers/android/binder.c?h=v6.5#n3658

3. Security critical: Binder is a critical part of Android's sandboxing
   strategy. Even Android's most de-privileged sandboxes (e.g. the
   Chrome renderer, or SW Codec) have direct access to Binder. More than
   just about any other component, it's important that Binder provide
   robust security, and itself be robust against security
   vulnerabilities.

It's #1 (high complexity) that has made continuing to evolve Binder and
resolving #2 (tech debt) exceptionally difficult without causing #3
(security issues). For Binder to continue to meet Android's needs, we
need better ways to manage (and reduce!) complexity without increasing
the risk.

The biggest change is obviously the choice of programming language. We
decided to use Rust because it directly addresses a number of the
challenges within Binder that we have faced during the last years. It
prevents mistakes with ref counting, locking, bounds checking, and also
does a lot to reduce the complexity of error handling. Additionally,
we've been able to use the more expressive type system to encode the
ownership semantics of the various structs and pointers, which takes the
complexity of managing object lifetimes out of the hands of the
programmer, reducing the risk of use-after-frees and similar problems.

Rust has many different pointer types that it uses to encode ownership
semantics into the type system, and this is probably one of the most
important aspects of how it helps in Binder. The Binder driver has a lot
of different objects that have complex ownership semantics; some
pointers own a refcount, some pointers have exclusive ownership, and
some pointers just reference the object and it is kept alive in some
other manner. With Rust, we can use a different pointer type for each
kind of pointer, which enables the compiler to enforce that the
ownership semantics are implemented correctly.

Another useful feature is Rust's error handling. Rust allows for more
simplified error handling with features such as destructors, and you get
compilation failures if errors are not properly handled. This means that
even though Rust requires you to spend more lines of code than C on
things such as writing down invariants that are left implicit in C, the
Rust driver is still slightly smaller than C binder: Rust is 5.5kLOC and
C is 5.8kLOC. (These numbers are excluding blank lines, comments,
binderfs, and any debugging facilities in C that are not yet implemented
in the Rust driver. The numbers include abstractions in rust/kernel/
that are unlikely to be used by other drivers than Binder.)

Although this rewrite completely rethinks how the code is structured and
how assumptions are enforced, we do not fundamentally change *how* the
driver does the things it does. A lot of careful thought has gone into
the existing design. The rewrite is aimed rather at improving code
health, structure, readability, robustness, security, maintainability
and extensibility. We also include more inline documentation, and
improve how assumptions in the code are enforced. Furthermore, all
unsafe code is annotated with a SAFETY comment that explains why it is
correct.

We have left the binderfs filesystem component in C. Rewriting it in
Rust would be a large amount of work and requires a lot of bindings to
the file system interfaces. Binderfs has not historically had the same
challenges with security and complexity, so rewriting binderfs seems to
have lower value than the rest of Binder.

Correctness and feature parity
------------------------------

Rust binder passes all tests that validate the correctness of Binder in
the Android Open Source Project. We can boot a device, and run a variety
of apps and functionality without issues. We have performed this both on
the Cuttlefish Android emulator device, and on a Pixel 6 Pro.

As for feature parity, Rust binder currently implements all features
that C binder supports, with the exception of some debugging facilities.
The missing debugging facilities will be added before we submit the Rust
implementation upstream.

Tracepoints
-----------

I did not include all of the tracepoints as I felt that the mechansim
for making C access fields of Rust structs should be discussed on list
separately. I also did not include the support for building Rust Binder
as a module since that requires exporting a bunch of additional symbols
on the C side.

Original RFC Link with old benchmark numbers:
	https://lore.kernel.org/r/20231101-rust-binder-v1-0-08ba9197f637@google.com

Co-developed-by: Wedson Almeida Filho <wedsonaf@gmail.com>
Signed-off-by: Wedson Almeida Filho <wedsonaf@gmail.com>
Co-developed-by: Matt Gilbride <mattgilbride@google.com>
Signed-off-by: Matt Gilbride <mattgilbride@google.com>
Acked-by: Carlos Llamas <cmllamas@google.com>
Acked-by: Paul Moore <paul@paul-moore.com>
Signed-off-by: Alice Ryhl <aliceryhl@google.com>
Link: https://lore.kernel.org/r/20250919-rust-binder-v2-1-a384b09f28dd@google.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/android/Kconfig

@@ -14,6 +14,19 @@ config ANDROID_BINDER_IPC
 	  Android process, using Binder to identify, invoke and pass arguments
 	  between said processes.
 
+config ANDROID_BINDER_IPC_RUST
+	bool "Rust version of Android Binder IPC Driver"
+	depends on RUST && MMU && !ANDROID_BINDER_IPC
+	help
+	  This enables the Rust implementation of the Binder driver.
+
+	  Binder is used in Android for both communication between processes,
+	  and remote method invocation.
+
+	  This means one Android process can call a method/routine in another
+	  Android process, using Binder to identify, invoke and pass arguments
+	  between said processes.
+
 config ANDROID_BINDERFS
 	bool "Android Binderfs filesystem"
 	depends on ANDROID_BINDER_IPC
@@ -28,7 +41,7 @@ config ANDROID_BINDERFS
 
 config ANDROID_BINDER_DEVICES
 	string "Android Binder devices"
-	depends on ANDROID_BINDER_IPC
+	depends on ANDROID_BINDER_IPC || ANDROID_BINDER_IPC_RUST
 	default "binder,hwbinder,vndbinder"
 	help
 	  Default value for the binder.devices parameter.

drivers/android/Makefile

@@ -4,3 +4,4 @@ ccflags-y += -I$(src)			# needed for trace events
 obj-$(CONFIG_ANDROID_BINDERFS)		+= binderfs.o
 obj-$(CONFIG_ANDROID_BINDER_IPC)	+= binder.o binder_alloc.o binder_netlink.o
 obj-$(CONFIG_ANDROID_BINDER_ALLOC_KUNIT_TEST)	+= tests/
+obj-$(CONFIG_ANDROID_BINDER_IPC_RUST)	+= binder/

drivers/android/binder/Makefile

@@ -0,0 +1,9 @@
+# SPDX-License-Identifier: GPL-2.0-only
+ccflags-y += -I$(src)	# needed for trace events
+
+obj-$(CONFIG_ANDROID_BINDER_IPC_RUST) += rust_binder.o
+rust_binder-y := \
+	rust_binder_main.o	\
+	rust_binderfs.o		\
+	rust_binder_events.o	\
+	page_range_helper.o

drivers/android/binder/allocation.rs

@@ -0,0 +1,602 @@
+// SPDX-License-Identifier: GPL-2.0
+
+// Copyright (C) 2025 Google LLC.
+
+use core::mem::{size_of, size_of_val, MaybeUninit};
+use core::ops::Range;
+
+use kernel::{
+    bindings,
+    fs::file::{File, FileDescriptorReservation},
+    prelude::*,
+    sync::{aref::ARef, Arc},
+    transmute::{AsBytes, FromBytes},
+    uaccess::UserSliceReader,
+    uapi,
+};
+
+use crate::{
+    deferred_close::DeferredFdCloser,
+    defs::*,
+    node::{Node, NodeRef},
+    process::Process,
+    DArc,
+};
+
+#[derive(Default)]
+pub(crate) struct AllocationInfo {
+    /// Range within the allocation where we can find the offsets to the object descriptors.
+    pub(crate) offsets: Option<Range<usize>>,
+    /// The target node of the transaction this allocation is associated to.
+    /// Not set for replies.
+    pub(crate) target_node: Option<NodeRef>,
+    /// When this allocation is dropped, call `pending_oneway_finished` on the node.
+    ///
+    /// This is used to serialize oneway transaction on the same node. Binder guarantees that
+    /// oneway transactions to the same node are delivered sequentially in the order they are sent.
+    pub(crate) oneway_node: Option<DArc<Node>>,
+    /// Zero the data in the buffer on free.
+    pub(crate) clear_on_free: bool,
+    /// List of files embedded in this transaction.
+    file_list: FileList,
+}
+
+/// Represents an allocation that the kernel is currently using.
+///
+/// When allocations are idle, the range allocator holds the data related to them.
+///
+/// # Invariants
+///
+/// This allocation corresponds to an allocation in the range allocator, so the relevant pages are
+/// marked in use in the page range.
+pub(crate) struct Allocation {
+    pub(crate) offset: usize,
+    size: usize,
+    pub(crate) ptr: usize,
+    pub(crate) process: Arc<Process>,
+    allocation_info: Option<AllocationInfo>,
+    free_on_drop: bool,
+    pub(crate) oneway_spam_detected: bool,
+    #[allow(dead_code)]
+    pub(crate) debug_id: usize,
+}
+
+impl Allocation {
+    pub(crate) fn new(
+        process: Arc<Process>,
+        debug_id: usize,
+        offset: usize,
+        size: usize,
+        ptr: usize,
+        oneway_spam_detected: bool,
+    ) -> Self {
+        Self {
+            process,
+            offset,
+            size,
+            ptr,
+            debug_id,
+            oneway_spam_detected,
+            allocation_info: None,
+            free_on_drop: true,
+        }
+    }
+
+    fn size_check(&self, offset: usize, size: usize) -> Result {
+        let overflow_fail = offset.checked_add(size).is_none();
+        let cmp_size_fail = offset.wrapping_add(size) > self.size;
+        if overflow_fail || cmp_size_fail {
+            return Err(EFAULT);
+        }
+        Ok(())
+    }
+
+    pub(crate) fn copy_into(
+        &self,
+        reader: &mut UserSliceReader,
+        offset: usize,
+        size: usize,
+    ) -> Result {
+        self.size_check(offset, size)?;
+
+        // SAFETY: While this object exists, the range allocator will keep the range allocated, and
+        // in turn, the pages will be marked as in use.
+        unsafe {
+            self.process
+                .pages
+                .copy_from_user_slice(reader, self.offset + offset, size)
+        }
+    }
+
+    pub(crate) fn read<T: FromBytes>(&self, offset: usize) -> Result<T> {
+        self.size_check(offset, size_of::<T>())?;
+
+        // SAFETY: While this object exists, the range allocator will keep the range allocated, and
+        // in turn, the pages will be marked as in use.
+        unsafe { self.process.pages.read(self.offset + offset) }
+    }
+
+    pub(crate) fn write<T: ?Sized>(&self, offset: usize, obj: &T) -> Result {
+        self.size_check(offset, size_of_val::<T>(obj))?;
+
+        // SAFETY: While this object exists, the range allocator will keep the range allocated, and
+        // in turn, the pages will be marked as in use.
+        unsafe { self.process.pages.write(self.offset + offset, obj) }
+    }
+
+    pub(crate) fn fill_zero(&self) -> Result {
+        // SAFETY: While this object exists, the range allocator will keep the range allocated, and
+        // in turn, the pages will be marked as in use.
+        unsafe { self.process.pages.fill_zero(self.offset, self.size) }
+    }
+
+    pub(crate) fn keep_alive(mut self) {
+        self.process
+            .buffer_make_freeable(self.offset, self.allocation_info.take());
+        self.free_on_drop = false;
+    }
+
+    pub(crate) fn set_info(&mut self, info: AllocationInfo) {
+        self.allocation_info = Some(info);
+    }
+
+    pub(crate) fn get_or_init_info(&mut self) -> &mut AllocationInfo {
+        self.allocation_info.get_or_insert_with(Default::default)
+    }
+
+    pub(crate) fn set_info_offsets(&mut self, offsets: Range<usize>) {
+        self.get_or_init_info().offsets = Some(offsets);
+    }
+
+    pub(crate) fn set_info_oneway_node(&mut self, oneway_node: DArc<Node>) {
+        self.get_or_init_info().oneway_node = Some(oneway_node);
+    }
+
+    pub(crate) fn set_info_clear_on_drop(&mut self) {
+        self.get_or_init_info().clear_on_free = true;
+    }
+
+    pub(crate) fn set_info_target_node(&mut self, target_node: NodeRef) {
+        self.get_or_init_info().target_node = Some(target_node);
+    }
+
+    /// Reserve enough space to push at least `num_fds` fds.
+    pub(crate) fn info_add_fd_reserve(&mut self, num_fds: usize) -> Result {
+        self.get_or_init_info()
+            .file_list
+            .files_to_translate
+            .reserve(num_fds, GFP_KERNEL)?;
+
+        Ok(())
+    }
+
+    pub(crate) fn info_add_fd(
+        &mut self,
+        file: ARef<File>,
+        buffer_offset: usize,
+        close_on_free: bool,
+    ) -> Result {
+        self.get_or_init_info().file_list.files_to_translate.push(
+            FileEntry {
+                file,
+                buffer_offset,
+                close_on_free,
+            },
+            GFP_KERNEL,
+        )?;
+
+        Ok(())
+    }
+
+    pub(crate) fn set_info_close_on_free(&mut self, cof: FdsCloseOnFree) {
+        self.get_or_init_info().file_list.close_on_free = cof.0;
+    }
+
+    pub(crate) fn translate_fds(&mut self) -> Result<TranslatedFds> {
+        let file_list = match self.allocation_info.as_mut() {
+            Some(info) => &mut info.file_list,
+            None => return Ok(TranslatedFds::new()),
+        };
+
+        let files = core::mem::take(&mut file_list.files_to_translate);
+
+        let num_close_on_free = files.iter().filter(|entry| entry.close_on_free).count();
+        let mut close_on_free = KVec::with_capacity(num_close_on_free, GFP_KERNEL)?;
+
+        let mut reservations = KVec::with_capacity(files.len(), GFP_KERNEL)?;
+        for file_info in files {
+            let res = FileDescriptorReservation::get_unused_fd_flags(bindings::O_CLOEXEC)?;
+            let fd = res.reserved_fd();
+            self.write::<u32>(file_info.buffer_offset, &fd)?;
+
+            reservations.push(
+                Reservation {
+                    res,
+                    file: file_info.file,
+                },
+                GFP_KERNEL,
+            )?;
+            if file_info.close_on_free {
+                close_on_free.push(fd, GFP_KERNEL)?;
+            }
+        }
+
+        Ok(TranslatedFds {
+            reservations,
+            close_on_free: FdsCloseOnFree(close_on_free),
+        })
+    }
+
+    /// Should the looper return to userspace when freeing this allocation?
+    pub(crate) fn looper_need_return_on_free(&self) -> bool {
+        // Closing fds involves pushing task_work for execution when we return to userspace. Hence,
+        // we should return to userspace asap if we are closing fds.
+        match self.allocation_info {
+            Some(ref info) => !info.file_list.close_on_free.is_empty(),
+            None => false,
+        }
+    }
+}
+
+impl Drop for Allocation {
+    fn drop(&mut self) {
+        if !self.free_on_drop {
+            return;
+        }
+
+        if let Some(mut info) = self.allocation_info.take() {
+            if let Some(oneway_node) = info.oneway_node.as_ref() {
+                oneway_node.pending_oneway_finished();
+            }
+
+            info.target_node = None;
+
+            if let Some(offsets) = info.offsets.clone() {
+                let view = AllocationView::new(self, offsets.start);
+                for i in offsets.step_by(size_of::<usize>()) {
+                    if view.cleanup_object(i).is_err() {
+                        pr_warn!("Error cleaning up object at offset {}\n", i)
+                    }
+                }
+            }
+
+            for &fd in &info.file_list.close_on_free {
+                let closer = match DeferredFdCloser::new(GFP_KERNEL) {
+                    Ok(closer) => closer,
+                    Err(kernel::alloc::AllocError) => {
+                        // Ignore allocation failures.
+                        break;
+                    }
+                };
+
+                // Here, we ignore errors. The operation can fail if the fd is not valid, or if the
+                // method is called from a kthread. However, this is always called from a syscall,
+                // so the latter case cannot happen, and we don't care about the first case.
+                let _ = closer.close_fd(fd);
+            }
+
+            if info.clear_on_free {
+                if let Err(e) = self.fill_zero() {
+                    pr_warn!("Failed to clear data on free: {:?}", e);
+                }
+            }
+        }
+
+        self.process.buffer_raw_free(self.ptr);
+    }
+}
+
+/// A wrapper around `Allocation` that is being created.
+///
+/// If the allocation is destroyed while wrapped in this wrapper, then the allocation will be
+/// considered to be part of a failed transaction. Successful transactions avoid that by calling
+/// `success`, which skips the destructor.
+#[repr(transparent)]
+pub(crate) struct NewAllocation(pub(crate) Allocation);
+
+impl NewAllocation {
+    pub(crate) fn success(self) -> Allocation {
+        // This skips the destructor.
+        //
+        // SAFETY: This type is `#[repr(transparent)]`, so the layout matches.
+        unsafe { core::mem::transmute(self) }
+    }
+}
+
+impl core::ops::Deref for NewAllocation {
+    type Target = Allocation;
+    fn deref(&self) -> &Allocation {
+        &self.0
+    }
+}
+
+impl core::ops::DerefMut for NewAllocation {
+    fn deref_mut(&mut self) -> &mut Allocation {
+        &mut self.0
+    }
+}
+
+/// A view into the beginning of an allocation.
+///
+/// All attempts to read or write outside of the view will fail. To intentionally access outside of
+/// this view, use the `alloc` field of this struct directly.
+pub(crate) struct AllocationView<'a> {
+    pub(crate) alloc: &'a mut Allocation,
+    limit: usize,
+}
+
+impl<'a> AllocationView<'a> {
+    pub(crate) fn new(alloc: &'a mut Allocation, limit: usize) -> Self {
+        AllocationView { alloc, limit }
+    }
+
+    pub(crate) fn read<T: FromBytes>(&self, offset: usize) -> Result<T> {
+        if offset.checked_add(size_of::<T>()).ok_or(EINVAL)? > self.limit {
+            return Err(EINVAL);
+        }
+        self.alloc.read(offset)
+    }
+
+    pub(crate) fn write<T: AsBytes>(&self, offset: usize, obj: &T) -> Result {
+        if offset.checked_add(size_of::<T>()).ok_or(EINVAL)? > self.limit {
+            return Err(EINVAL);
+        }
+        self.alloc.write(offset, obj)
+    }
+
+    pub(crate) fn copy_into(
+        &self,
+        reader: &mut UserSliceReader,
+        offset: usize,
+        size: usize,
+    ) -> Result {
+        if offset.checked_add(size).ok_or(EINVAL)? > self.limit {
+            return Err(EINVAL);
+        }
+        self.alloc.copy_into(reader, offset, size)
+    }
+
+    pub(crate) fn transfer_binder_object(
+        &self,
+        offset: usize,
+        obj: &uapi::flat_binder_object,
+        strong: bool,
+        node_ref: NodeRef,
+    ) -> Result {
+        let mut newobj = FlatBinderObject::default();
+        let node = node_ref.node.clone();
+        if Arc::ptr_eq(&node_ref.node.owner, &self.alloc.process) {
+            // The receiving process is the owner of the node, so send it a binder object (instead
+            // of a handle).
+            let (ptr, cookie) = node.get_id();
+            newobj.hdr.type_ = if strong {
+                BINDER_TYPE_BINDER
+            } else {
+                BINDER_TYPE_WEAK_BINDER
+            };
+            newobj.flags = obj.flags;
+            newobj.__bindgen_anon_1.binder = ptr as _;
+            newobj.cookie = cookie as _;
+            self.write(offset, &newobj)?;
+            // Increment the user ref count on the node. It will be decremented as part of the
+            // destruction of the buffer, when we see a binder or weak-binder object.
+            node.update_refcount(true, 1, strong);
+        } else {
+            // The receiving process is different from the owner, so we need to insert a handle to
+            // the binder object.
+            let handle = self
+                .alloc
+                .process
+                .as_arc_borrow()
+                .insert_or_update_handle(node_ref, false)?;
+            newobj.hdr.type_ = if strong {
+                BINDER_TYPE_HANDLE
+            } else {
+                BINDER_TYPE_WEAK_HANDLE
+            };
+            newobj.flags = obj.flags;
+            newobj.__bindgen_anon_1.handle = handle;
+            if self.write(offset, &newobj).is_err() {
+                // Decrement ref count on the handle we just created.
+                let _ = self
+                    .alloc
+                    .process
+                    .as_arc_borrow()
+                    .update_ref(handle, false, strong);
+                return Err(EINVAL);
+            }
+        }
+
+        Ok(())
+    }
+
+    fn cleanup_object(&self, index_offset: usize) -> Result {
+        let offset = self.alloc.read(index_offset)?;
+        let header = self.read::<BinderObjectHeader>(offset)?;
+        match header.type_ {
+            BINDER_TYPE_WEAK_BINDER | BINDER_TYPE_BINDER => {
+                let obj = self.read::<FlatBinderObject>(offset)?;
+                let strong = header.type_ == BINDER_TYPE_BINDER;
+                // SAFETY: The type is `BINDER_TYPE_{WEAK_}BINDER`, so the `binder` field is
+                // populated.
+                let ptr = unsafe { obj.__bindgen_anon_1.binder };
+                let cookie = obj.cookie;
+                self.alloc.process.update_node(ptr, cookie, strong);
+                Ok(())
+            }
+            BINDER_TYPE_WEAK_HANDLE | BINDER_TYPE_HANDLE => {
+                let obj = self.read::<FlatBinderObject>(offset)?;
+                let strong = header.type_ == BINDER_TYPE_HANDLE;
+                // SAFETY: The type is `BINDER_TYPE_{WEAK_}HANDLE`, so the `handle` field is
+                // populated.
+                let handle = unsafe { obj.__bindgen_anon_1.handle };
+                self.alloc
+                    .process
+                    .as_arc_borrow()
+                    .update_ref(handle, false, strong)
+            }
+            _ => Ok(()),
+        }
+    }
+}
+
+/// A binder object as it is serialized.
+///
+/// # Invariants
+///
+/// All bytes must be initialized, and the value of `self.hdr.type_` must be one of the allowed
+/// types.
+#[repr(C)]
+pub(crate) union BinderObject {
+    hdr: uapi::binder_object_header,
+    fbo: uapi::flat_binder_object,
+    fdo: uapi::binder_fd_object,
+    bbo: uapi::binder_buffer_object,
+    fdao: uapi::binder_fd_array_object,
+}
+
+/// A view into a `BinderObject` that can be used in a match statement.
+pub(crate) enum BinderObjectRef<'a> {
+    Binder(&'a mut uapi::flat_binder_object),
+    Handle(&'a mut uapi::flat_binder_object),
+    Fd(&'a mut uapi::binder_fd_object),
+    Ptr(&'a mut uapi::binder_buffer_object),
+    Fda(&'a mut uapi::binder_fd_array_object),
+}
+
+impl BinderObject {
+    pub(crate) fn read_from(reader: &mut UserSliceReader) -> Result<BinderObject> {
+        let object = Self::read_from_inner(|slice| {
+            let read_len = usize::min(slice.len(), reader.len());
+            reader.clone_reader().read_slice(&mut slice[..read_len])?;
+            Ok(())
+        })?;
+
+        // If we used a object type smaller than the largest object size, then we've read more
+        // bytes than we needed to. However, we used `.clone_reader()` to avoid advancing the
+        // original reader. Now, we call `skip` so that the caller's reader is advanced by the
+        // right amount.
+        //
+        // The `skip` call fails if the reader doesn't have `size` bytes available. This could
+        // happen if the type header corresponds to an object type that is larger than the rest of
+        // the reader.
+        //
+        // Any extra bytes beyond the size of the object are inaccessible after this call, so
+        // reading them again from the `reader` later does not result in TOCTOU bugs.
+        reader.skip(object.size())?;
+
+        Ok(object)
+    }
+
+    /// Use the provided reader closure to construct a `BinderObject`.
+    ///
+    /// The closure should write the bytes for the object into the provided slice.
+    pub(crate) fn read_from_inner<R>(reader: R) -> Result<BinderObject>
+    where
+        R: FnOnce(&mut [u8; size_of::<BinderObject>()]) -> Result<()>,
+    {
+        let mut obj = MaybeUninit::<BinderObject>::zeroed();
+
+        // SAFETY: The lengths of `BinderObject` and `[u8; size_of::<BinderObject>()]` are equal,
+        // and the byte array has an alignment requirement of one, so the pointer cast is okay.
+        // Additionally, `obj` was initialized to zeros, so the byte array will not be
+        // uninitialized.
+        (reader)(unsafe { &mut *obj.as_mut_ptr().cast() })?;
+
+        // SAFETY: The entire object is initialized, so accessing this field is safe.
+        let type_ = unsafe { obj.assume_init_ref().hdr.type_ };
+        if Self::type_to_size(type_).is_none() {
+            // The value of `obj.hdr_type_` was invalid.
+            return Err(EINVAL);
+        }
+
+        // SAFETY: All bytes are initialized (since we zeroed them at the start) and we checked
+        // that `self.hdr.type_` is one of the allowed types, so the type invariants are satisfied.
+        unsafe { Ok(obj.assume_init()) }
+    }
+
+    pub(crate) fn as_ref(&mut self) -> BinderObjectRef<'_> {
+        use BinderObjectRef::*;
+        // SAFETY: The constructor ensures that all bytes of `self` are initialized, and all
+        // variants of this union accept all initialized bit patterns.
+        unsafe {
+            match self.hdr.type_ {
+                BINDER_TYPE_WEAK_BINDER | BINDER_TYPE_BINDER => Binder(&mut self.fbo),
+                BINDER_TYPE_WEAK_HANDLE | BINDER_TYPE_HANDLE => Handle(&mut self.fbo),
+                BINDER_TYPE_FD => Fd(&mut self.fdo),
+                BINDER_TYPE_PTR => Ptr(&mut self.bbo),
+                BINDER_TYPE_FDA => Fda(&mut self.fdao),
+                // SAFETY: By the type invariant, the value of `self.hdr.type_` cannot have any
+                // other value than the ones checked above.
+                _ => core::hint::unreachable_unchecked(),
+            }
+        }
+    }
+
+    pub(crate) fn size(&self) -> usize {
+        // SAFETY: The entire object is initialized, so accessing this field is safe.
+        let type_ = unsafe { self.hdr.type_ };
+
+        // SAFETY: The type invariants guarantee that the type field is correct.
+        unsafe { Self::type_to_size(type_).unwrap_unchecked() }
+    }
+
+    fn type_to_size(type_: u32) -> Option<usize> {
+        match type_ {
+            BINDER_TYPE_WEAK_BINDER => Some(size_of::<uapi::flat_binder_object>()),
+            BINDER_TYPE_BINDER => Some(size_of::<uapi::flat_binder_object>()),
+            BINDER_TYPE_WEAK_HANDLE => Some(size_of::<uapi::flat_binder_object>()),
+            BINDER_TYPE_HANDLE => Some(size_of::<uapi::flat_binder_object>()),
+            BINDER_TYPE_FD => Some(size_of::<uapi::binder_fd_object>()),
+            BINDER_TYPE_PTR => Some(size_of::<uapi::binder_buffer_object>()),
+            BINDER_TYPE_FDA => Some(size_of::<uapi::binder_fd_array_object>()),
+            _ => None,
+        }
+    }
+}
+
+#[derive(Default)]
+struct FileList {
+    files_to_translate: KVec<FileEntry>,
+    close_on_free: KVec<u32>,
+}
+
+struct FileEntry {
+    /// The file for which a descriptor will be created in the recipient process.
+    file: ARef<File>,
+    /// The offset in the buffer where the file descriptor is stored.
+    buffer_offset: usize,
+    /// Whether this fd should be closed when the allocation is freed.
+    close_on_free: bool,
+}
+
+pub(crate) struct TranslatedFds {
+    reservations: KVec<Reservation>,
+    /// If commit is called, then these fds should be closed. (If commit is not called, then they
+    /// shouldn't be closed.)
+    close_on_free: FdsCloseOnFree,
+}
+
+struct Reservation {
+    res: FileDescriptorReservation,
+    file: ARef<File>,
+}
+
+impl TranslatedFds {
+    pub(crate) fn new() -> Self {
+        Self {
+            reservations: KVec::new(),
+            close_on_free: FdsCloseOnFree(KVec::new()),
+        }
+    }
+
+    pub(crate) fn commit(self) -> FdsCloseOnFree {
+        for entry in self.reservations {
+            entry.res.fd_install(entry.file);
+        }
+
+        self.close_on_free
+    }
+}
+
+pub(crate) struct FdsCloseOnFree(KVec<u32>);

drivers/android/binder/context.rs

@@ -0,0 +1,180 @@
+// SPDX-License-Identifier: GPL-2.0
+
+// Copyright (C) 2025 Google LLC.
+
+use kernel::{
+    error::Error,
+    list::{List, ListArc, ListLinks},
+    prelude::*,
+    security,
+    str::{CStr, CString},
+    sync::{Arc, Mutex},
+    task::Kuid,
+};
+
+use crate::{error::BinderError, node::NodeRef, process::Process};
+
+kernel::sync::global_lock! {
+    // SAFETY: We call `init` in the module initializer, so it's initialized before first use.
+    pub(crate) unsafe(uninit) static CONTEXTS: Mutex<ContextList> = ContextList {
+        list: List::new(),
+    };
+}
+
+pub(crate) struct ContextList {
+    list: List<Context>,
+}
+
+pub(crate) fn get_all_contexts() -> Result<KVec<Arc<Context>>> {
+    let lock = CONTEXTS.lock();
+
+    let count = lock.list.iter().count();
+
+    let mut ctxs = KVec::with_capacity(count, GFP_KERNEL)?;
+    for ctx in &lock.list {
+        ctxs.push(Arc::from(ctx), GFP_KERNEL)?;
+    }
+    Ok(ctxs)
+}
+
+/// This struct keeps track of the processes using this context, and which process is the context
+/// manager.
+struct Manager {
+    node: Option<NodeRef>,
+    uid: Option<Kuid>,
+    all_procs: List<Process>,
+}
+
+/// There is one context per binder file (/dev/binder, /dev/hwbinder, etc)
+#[pin_data]
+pub(crate) struct Context {
+    #[pin]
+    manager: Mutex<Manager>,
+    pub(crate) name: CString,
+    #[pin]
+    links: ListLinks,
+}
+
+kernel::list::impl_list_arc_safe! {
+    impl ListArcSafe<0> for Context { untracked; }
+}
+kernel::list::impl_list_item! {
+    impl ListItem<0> for Context {
+        using ListLinks { self.links };
+    }
+}
+
+impl Context {
+    pub(crate) fn new(name: &CStr) -> Result<Arc<Self>> {
+        let name = CString::try_from(name)?;
+        let list_ctx = ListArc::pin_init::<Error>(
+            try_pin_init!(Context {
+                name,
+                links <- ListLinks::new(),
+                manager <- kernel::new_mutex!(Manager {
+                    all_procs: List::new(),
+                    node: None,
+                    uid: None,
+                }, "Context::manager"),
+            }),
+            GFP_KERNEL,
+        )?;
+
+        let ctx = list_ctx.clone_arc();
+        CONTEXTS.lock().list.push_back(list_ctx);
+
+        Ok(ctx)
+    }
+
+    /// Called when the file for this context is unlinked.
+    ///
+    /// No-op if called twice.
+    pub(crate) fn deregister(&self) {
+        // SAFETY: We never add the context to any other linked list than this one, so it is either
+        // in this list, or not in any list.
+        unsafe { CONTEXTS.lock().list.remove(self) };
+    }
+
+    pub(crate) fn register_process(self: &Arc<Self>, proc: ListArc<Process>) {
+        if !Arc::ptr_eq(self, &proc.ctx) {
+            pr_err!("Context::register_process called on the wrong context.");
+            return;
+        }
+        self.manager.lock().all_procs.push_back(proc);
+    }
+
+    pub(crate) fn deregister_process(self: &Arc<Self>, proc: &Process) {
+        if !Arc::ptr_eq(self, &proc.ctx) {
+            pr_err!("Context::deregister_process called on the wrong context.");
+            return;
+        }
+        // SAFETY: We just checked that this is the right list.
+        unsafe { self.manager.lock().all_procs.remove(proc) };
+    }
+
+    pub(crate) fn set_manager_node(&self, node_ref: NodeRef) -> Result {
+        let mut manager = self.manager.lock();
+        if manager.node.is_some() {
+            pr_warn!("BINDER_SET_CONTEXT_MGR already set");
+            return Err(EBUSY);
+        }
+        security::binder_set_context_mgr(&node_ref.node.owner.cred)?;
+
+        // If the context manager has been set before, ensure that we use the same euid.
+        let caller_uid = Kuid::current_euid();
+        if let Some(ref uid) = manager.uid {
+            if *uid != caller_uid {
+                return Err(EPERM);
+            }
+        }
+
+        manager.node = Some(node_ref);
+        manager.uid = Some(caller_uid);
+        Ok(())
+    }
+
+    pub(crate) fn unset_manager_node(&self) {
+        let node_ref = self.manager.lock().node.take();
+        drop(node_ref);
+    }
+
+    pub(crate) fn get_manager_node(&self, strong: bool) -> Result<NodeRef, BinderError> {
+        self.manager
+            .lock()
+            .node
+            .as_ref()
+            .ok_or_else(BinderError::new_dead)?
+            .clone(strong)
+            .map_err(BinderError::from)
+    }
+
+    pub(crate) fn for_each_proc<F>(&self, mut func: F)
+    where
+        F: FnMut(&Process),
+    {
+        let lock = self.manager.lock();
+        for proc in &lock.all_procs {
+            func(&proc);
+        }
+    }
+
+    pub(crate) fn get_all_procs(&self) -> Result<KVec<Arc<Process>>> {
+        let lock = self.manager.lock();
+        let count = lock.all_procs.iter().count();
+
+        let mut procs = KVec::with_capacity(count, GFP_KERNEL)?;
+        for proc in &lock.all_procs {
+            procs.push(Arc::from(proc), GFP_KERNEL)?;
+        }
+        Ok(procs)
+    }
+
+    pub(crate) fn get_procs_with_pid(&self, pid: i32) -> Result<KVec<Arc<Process>>> {
+        let orig = self.get_all_procs()?;
+        let mut backing = KVec::with_capacity(orig.len(), GFP_KERNEL)?;
+        for proc in orig.into_iter().filter(|proc| proc.task.pid() == pid) {
+            backing.push(proc, GFP_KERNEL)?;
+        }
+        Ok(backing)
+    }
+}

drivers/android/binder/deferred_close.rs

@@ -0,0 +1,204 @@
+// SPDX-License-Identifier: GPL-2.0
+
+// Copyright (C) 2025 Google LLC.
+
+//! Logic for closing files in a deferred manner.
+//!
+//! This file could make sense to have in `kernel::fs`, but it was rejected for being too
+//! Binder-specific.
+
+use core::mem::MaybeUninit;
+use kernel::{
+    alloc::{AllocError, Flags},
+    bindings,
+    prelude::*,
+};
+
+/// Helper used for closing file descriptors in a way that is safe even if the file is currently
+/// held using `fdget`.
+///
+/// Additional motivation can be found in commit 80cd795630d6 ("binder: fix use-after-free due to
+/// ksys_close() during fdget()") and in the comments on `binder_do_fd_close`.
+pub(crate) struct DeferredFdCloser {
+    inner: KBox<DeferredFdCloserInner>,
+}
+
+/// SAFETY: This just holds an allocation with no real content, so there's no safety issue with
+/// moving it across threads.
+unsafe impl Send for DeferredFdCloser {}
+/// SAFETY: This just holds an allocation with no real content, so there's no safety issue with
+/// moving it across threads.
+unsafe impl Sync for DeferredFdCloser {}
+
+/// # Invariants
+///
+/// If the `file` pointer is non-null, then it points at a `struct file` and owns a refcount to
+/// that file.
+#[repr(C)]
+struct DeferredFdCloserInner {
+    twork: MaybeUninit<bindings::callback_head>,
+    file: *mut bindings::file,
+}
+
+impl DeferredFdCloser {
+    /// Create a new [`DeferredFdCloser`].
+    pub(crate) fn new(flags: Flags) -> Result<Self, AllocError> {
+        Ok(Self {
+            // INVARIANT: The `file` pointer is null, so the type invariant does not apply.
+            inner: KBox::new(
+                DeferredFdCloserInner {
+                    twork: MaybeUninit::uninit(),
+                    file: core::ptr::null_mut(),
+                },
+                flags,
+            )?,
+        })
+    }
+
+    /// Schedule a task work that closes the file descriptor when this task returns to userspace.
+    ///
+    /// Fails if this is called from a context where we cannot run work when returning to
+    /// userspace. (E.g., from a kthread.)
+    pub(crate) fn close_fd(self, fd: u32) -> Result<(), DeferredFdCloseError> {
+        use bindings::task_work_notify_mode_TWA_RESUME as TWA_RESUME;
+
+        // In this method, we schedule the task work before closing the file. This is because
+        // scheduling a task work is fallible, and we need to know whether it will fail before we
+        // attempt to close the file.
+
+        // Task works are not available on kthreads.
+        let current = kernel::current!();
+
+        // Check if this is a kthread.
+        // SAFETY: Reading `flags` from a task is always okay.
+        if unsafe { ((*current.as_ptr()).flags & bindings::PF_KTHREAD) != 0 } {
+            return Err(DeferredFdCloseError::TaskWorkUnavailable);
+        }
+
+        // Transfer ownership of the box's allocation to a raw pointer. This disables the
+        // destructor, so we must manually convert it back to a KBox to drop it.
+        //
+        // Until we convert it back to a `KBox`, there are no aliasing requirements on this
+        // pointer.
+        let inner = KBox::into_raw(self.inner);
+
+        // The `callback_head` field is first in the struct, so this cast correctly gives us a
+        // pointer to the field.
+        let callback_head = inner.cast::<bindings::callback_head>();
+        // SAFETY: This pointer offset operation does not go out-of-bounds.
+        let file_field = unsafe { core::ptr::addr_of_mut!((*inner).file) };
+
+        let current = current.as_ptr();
+
+        // SAFETY: This function currently has exclusive access to the `DeferredFdCloserInner`, so
+        // it is okay for us to perform unsynchronized writes to its `callback_head` field.
+        unsafe { bindings::init_task_work(callback_head, Some(Self::do_close_fd)) };
+
+        // SAFETY: This inserts the `DeferredFdCloserInner` into the task workqueue for the current
+        // task. If this operation is successful, then this transfers exclusive ownership of the
+        // `callback_head` field to the C side until it calls `do_close_fd`, and we don't touch or
+        // invalidate the field during that time.
+        //
+        // When the C side calls `do_close_fd`, the safety requirements of that method are
+        // satisfied because when a task work is executed, the callback is given ownership of the
+        // pointer.
+        //
+        // The file pointer is currently null. If it is changed to be non-null before `do_close_fd`
+        // is called, then that change happens due to the write at the end of this function, and
+        // that write has a safety comment that explains why the refcount can be dropped when
+        // `do_close_fd` runs.
+        let res = unsafe { bindings::task_work_add(current, callback_head, TWA_RESUME) };
+
+        if res != 0 {
+            // SAFETY: Scheduling the task work failed, so we still have ownership of the box, so
+            // we may destroy it.
+            unsafe { drop(KBox::from_raw(inner)) };
+
+            return Err(DeferredFdCloseError::TaskWorkUnavailable);
+        }
+
+        // This removes the fd from the fd table in `current`. The file is not fully closed until
+        // `filp_close` is called. We are given ownership of one refcount to the file.
+        //
+        // SAFETY: This is safe no matter what `fd` is. If the `fd` is valid (that is, if the
+        // pointer is non-null), then we call `filp_close` on the returned pointer as required by
+        // `file_close_fd`.
+        let file = unsafe { bindings::file_close_fd(fd) };
+        if file.is_null() {
+            // We don't clean up the task work since that might be expensive if the task work queue
+            // is long. Just let it execute and let it clean up for itself.
+            return Err(DeferredFdCloseError::BadFd);
+        }
+
+        // Acquire a second refcount to the file.
+        //
+        // SAFETY: The `file` pointer points at a file with a non-zero refcount.
+        unsafe { bindings::get_file(file) };
+
+        // This method closes the fd, consuming one of our two refcounts. There could be active
+        // light refcounts created from that fd, so we must ensure that the file has a positive
+        // refcount for the duration of those active light refcounts. We do that by holding on to
+        // the second refcount until the current task returns to userspace.
+        //
+        // SAFETY: The `file` pointer is valid. Passing `current->files` as the file table to close
+        // it in is correct, since we just got the `fd` from `file_close_fd` which also uses
+        // `current->files`.
+        //
+        // Note: fl_owner_t is currently a void pointer.
+        unsafe { bindings::filp_close(file, (*current).files as bindings::fl_owner_t) };
+
+        // We update the file pointer that the task work is supposed to fput. This transfers
+        // ownership of our last refcount.
+        //
+        // INVARIANT: This changes the `file` field of a `DeferredFdCloserInner` from null to
+        // non-null. This doesn't break the type invariant for `DeferredFdCloserInner` because we
+        // still own a refcount to the file, so we can pass ownership of that refcount to the
+        // `DeferredFdCloserInner`.
+        //
+        // When `do_close_fd` runs, it must be safe for it to `fput` the refcount. However, this is
+        // the case because all light refcounts that are associated with the fd we closed
+        // previously must be dropped when `do_close_fd`, since light refcounts must be dropped
+        // before returning to userspace.
+        //
+        // SAFETY: Task works are executed on the current thread right before we return to
+        // userspace, so this write is guaranteed to happen before `do_close_fd` is called, which
+        // means that a race is not possible here.
+        unsafe { *file_field = file };
+
+        Ok(())
+    }
+
+    /// # Safety
+    ///
+    /// The provided pointer must point at the `twork` field of a `DeferredFdCloserInner` stored in
+    /// a `KBox`, and the caller must pass exclusive ownership of that `KBox`. Furthermore, if the
+    /// file pointer is non-null, then it must be okay to release the refcount by calling `fput`.
+    unsafe extern "C" fn do_close_fd(inner: *mut bindings::callback_head) {
+        // SAFETY: The caller just passed us ownership of this box.
+        let inner = unsafe { KBox::from_raw(inner.cast::<DeferredFdCloserInner>()) };
+        if !inner.file.is_null() {
+            // SAFETY: By the type invariants, we own a refcount to this file, and the caller
+            // guarantees that dropping the refcount now is okay.
+            unsafe { bindings::fput(inner.file) };
+        }
+        // The allocation is freed when `inner` goes out of scope.
+    }
+}
+
+/// Represents a failure to close an fd in a deferred manner.
+#[derive(Copy, Clone, Debug, Eq, PartialEq)]
+pub(crate) enum DeferredFdCloseError {
+    /// Closing the fd failed because we were unable to schedule a task work.
+    TaskWorkUnavailable,
+    /// Closing the fd failed because the fd does not exist.
+    BadFd,
+}
+
+impl From<DeferredFdCloseError> for Error {
+    fn from(err: DeferredFdCloseError) -> Error {
+        match err {
+            DeferredFdCloseError::TaskWorkUnavailable => ESRCH,
+            DeferredFdCloseError::BadFd => EBADF,
+        }
+    }
+}

drivers/android/binder/defs.rs

@@ -0,0 +1,182 @@
+// SPDX-License-Identifier: GPL-2.0
+
+// Copyright (C) 2025 Google LLC.
+
+use core::mem::MaybeUninit;
+use core::ops::{Deref, DerefMut};
+use kernel::{
+    transmute::{AsBytes, FromBytes},
+    uapi::{self, *},
+};
+
+macro_rules! pub_no_prefix {
+    ($prefix:ident, $($newname:ident),+ $(,)?) => {
+        $(pub(crate) const $newname: u32 = kernel::macros::concat_idents!($prefix, $newname);)+
+    };
+}
+
+pub_no_prefix!(
+    binder_driver_return_protocol_,
+    BR_TRANSACTION,
+    BR_TRANSACTION_SEC_CTX,
+    BR_REPLY,
+    BR_DEAD_REPLY,
+    BR_FAILED_REPLY,
+    BR_FROZEN_REPLY,
+    BR_NOOP,
+    BR_SPAWN_LOOPER,
+    BR_TRANSACTION_COMPLETE,
+    BR_TRANSACTION_PENDING_FROZEN,
+    BR_ONEWAY_SPAM_SUSPECT,
+    BR_OK,
+    BR_ERROR,
+    BR_INCREFS,
+    BR_ACQUIRE,
+    BR_RELEASE,
+    BR_DECREFS,
+    BR_DEAD_BINDER,
+    BR_CLEAR_DEATH_NOTIFICATION_DONE,
+    BR_FROZEN_BINDER,
+    BR_CLEAR_FREEZE_NOTIFICATION_DONE,
+);
+
+pub_no_prefix!(
+    binder_driver_command_protocol_,
+    BC_TRANSACTION,
+    BC_TRANSACTION_SG,
+    BC_REPLY,
+    BC_REPLY_SG,
+    BC_FREE_BUFFER,
+    BC_ENTER_LOOPER,
+    BC_EXIT_LOOPER,
+    BC_REGISTER_LOOPER,
+    BC_INCREFS,
+    BC_ACQUIRE,
+    BC_RELEASE,
+    BC_DECREFS,
+    BC_INCREFS_DONE,
+    BC_ACQUIRE_DONE,
+    BC_REQUEST_DEATH_NOTIFICATION,
+    BC_CLEAR_DEATH_NOTIFICATION,
+    BC_DEAD_BINDER_DONE,
+    BC_REQUEST_FREEZE_NOTIFICATION,
+    BC_CLEAR_FREEZE_NOTIFICATION,
+    BC_FREEZE_NOTIFICATION_DONE,
+);
+
+pub_no_prefix!(
+    flat_binder_object_flags_,
+    FLAT_BINDER_FLAG_ACCEPTS_FDS,
+    FLAT_BINDER_FLAG_TXN_SECURITY_CTX
+);
+
+pub_no_prefix!(
+    transaction_flags_,
+    TF_ONE_WAY,
+    TF_ACCEPT_FDS,
+    TF_CLEAR_BUF,
+    TF_UPDATE_TXN
+);
+
+pub(crate) use uapi::{
+    BINDER_TYPE_BINDER, BINDER_TYPE_FD, BINDER_TYPE_FDA, BINDER_TYPE_HANDLE, BINDER_TYPE_PTR,
+    BINDER_TYPE_WEAK_BINDER, BINDER_TYPE_WEAK_HANDLE,
+};
+
+macro_rules! decl_wrapper {
+    ($newname:ident, $wrapped:ty) => {
+        // Define a wrapper around the C type. Use `MaybeUninit` to enforce that the value of
+        // padding bytes must be preserved.
+        #[derive(Copy, Clone)]
+        #[repr(transparent)]
+        pub(crate) struct $newname(MaybeUninit<$wrapped>);
+
+        // SAFETY: This macro is only used with types where this is ok.
+        unsafe impl FromBytes for $newname {}
+        // SAFETY: This macro is only used with types where this is ok.
+        unsafe impl AsBytes for $newname {}
+
+        impl Deref for $newname {
+            type Target = $wrapped;
+            fn deref(&self) -> &Self::Target {
+                // SAFETY: We use `MaybeUninit` only to preserve padding. The value must still
+                // always be valid.
+                unsafe { self.0.assume_init_ref() }
+            }
+        }
+
+        impl DerefMut for $newname {
+            fn deref_mut(&mut self) -> &mut Self::Target {
+                // SAFETY: We use `MaybeUninit` only to preserve padding. The value must still
+                // always be valid.
+                unsafe { self.0.assume_init_mut() }
+            }
+        }
+
+        impl Default for $newname {
+            fn default() -> Self {
+                // Create a new value of this type where all bytes (including padding) are zeroed.
+                Self(MaybeUninit::zeroed())
+            }
+        }
+    };
+}
+
+decl_wrapper!(BinderNodeDebugInfo, uapi::binder_node_debug_info);
+decl_wrapper!(BinderNodeInfoForRef, uapi::binder_node_info_for_ref);
+decl_wrapper!(FlatBinderObject, uapi::flat_binder_object);
+decl_wrapper!(BinderFdObject, uapi::binder_fd_object);
+decl_wrapper!(BinderFdArrayObject, uapi::binder_fd_array_object);
+decl_wrapper!(BinderObjectHeader, uapi::binder_object_header);
+decl_wrapper!(BinderBufferObject, uapi::binder_buffer_object);
+decl_wrapper!(BinderTransactionData, uapi::binder_transaction_data);
+decl_wrapper!(
+    BinderTransactionDataSecctx,
+    uapi::binder_transaction_data_secctx
+);
+decl_wrapper!(BinderTransactionDataSg, uapi::binder_transaction_data_sg);
+decl_wrapper!(BinderWriteRead, uapi::binder_write_read);
+decl_wrapper!(BinderVersion, uapi::binder_version);
+decl_wrapper!(BinderFrozenStatusInfo, uapi::binder_frozen_status_info);
+decl_wrapper!(BinderFreezeInfo, uapi::binder_freeze_info);
+decl_wrapper!(BinderFrozenStateInfo, uapi::binder_frozen_state_info);
+decl_wrapper!(BinderHandleCookie, uapi::binder_handle_cookie);
+decl_wrapper!(ExtendedError, uapi::binder_extended_error);
+
+impl BinderVersion {
+    pub(crate) fn current() -> Self {
+        Self(MaybeUninit::new(uapi::binder_version {
+            protocol_version: BINDER_CURRENT_PROTOCOL_VERSION as _,
+        }))
+    }
+}
+
+impl BinderTransactionData {
+    pub(crate) fn with_buffers_size(self, buffers_size: u64) -> BinderTransactionDataSg {
+        BinderTransactionDataSg(MaybeUninit::new(uapi::binder_transaction_data_sg {
+            transaction_data: *self,
+            buffers_size,
+        }))
+    }
+}
+
+impl BinderTransactionDataSecctx {
+    /// View the inner data as wrapped in `BinderTransactionData`.
+    pub(crate) fn tr_data(&mut self) -> &mut BinderTransactionData {
+        // SAFETY: Transparent wrapper is safe to transmute.
+        unsafe {
+            &mut *(&mut self.transaction_data as *mut uapi::binder_transaction_data
+                as *mut BinderTransactionData)
+        }
+    }
+}
+
+impl ExtendedError {
+    pub(crate) fn new(id: u32, command: u32, param: i32) -> Self {
+        Self(MaybeUninit::new(uapi::binder_extended_error {
+            id,
+            command,
+            param,
+        }))
+    }
+}

drivers/android/binder/error.rs

@@ -0,0 +1,99 @@
+// SPDX-License-Identifier: GPL-2.0
+
+// Copyright (C) 2025 Google LLC.
+
+use kernel::prelude::*;
+
+use crate::defs::*;
+
+pub(crate) type BinderResult<T = ()> = core::result::Result<T, BinderError>;
+
+/// An error that will be returned to userspace via the `BINDER_WRITE_READ` ioctl rather than via
+/// errno.
+pub(crate) struct BinderError {
+    pub(crate) reply: u32,
+    source: Option<Error>,
+}
+
+impl BinderError {
+    pub(crate) fn new_dead() -> Self {
+        Self {
+            reply: BR_DEAD_REPLY,
+            source: None,
+        }
+    }
+
+    pub(crate) fn new_frozen() -> Self {
+        Self {
+            reply: BR_FROZEN_REPLY,
+            source: None,
+        }
+    }
+
+    pub(crate) fn new_frozen_oneway() -> Self {
+        Self {
+            reply: BR_TRANSACTION_PENDING_FROZEN,
+            source: None,
+        }
+    }
+
+    pub(crate) fn is_dead(&self) -> bool {
+        self.reply == BR_DEAD_REPLY
+    }
+
+    pub(crate) fn as_errno(&self) -> kernel::ffi::c_int {
+        self.source.unwrap_or(EINVAL).to_errno()
+    }
+
+    pub(crate) fn should_pr_warn(&self) -> bool {
+        self.source.is_some()
+    }
+}
+
+/// Convert an errno into a `BinderError` and store the errno used to construct it. The errno
+/// should be stored as the thread's extended error when given to userspace.
+impl From<Error> for BinderError {
+    fn from(source: Error) -> Self {
+        Self {
+            reply: BR_FAILED_REPLY,
+            source: Some(source),
+        }
+    }
+}
+
+impl From<kernel::fs::file::BadFdError> for BinderError {
+    fn from(source: kernel::fs::file::BadFdError) -> Self {
+        BinderError::from(Error::from(source))
+    }
+}
+
+impl From<kernel::alloc::AllocError> for BinderError {
+    fn from(_: kernel::alloc::AllocError) -> Self {
+        Self {
+            reply: BR_FAILED_REPLY,
+            source: Some(ENOMEM),
+        }
+    }
+}
+
+impl core::fmt::Debug for BinderError {
+    fn fmt(&self, f: &mut core::fmt::Formatter<'_>) -> core::fmt::Result {
+        match self.reply {
+            BR_FAILED_REPLY => match self.source.as_ref() {
+                Some(source) => f
+                    .debug_struct("BR_FAILED_REPLY")
+                    .field("source", source)
+                    .finish(),
+                None => f.pad("BR_FAILED_REPLY"),
+            },
+            BR_DEAD_REPLY => f.pad("BR_DEAD_REPLY"),
+            BR_FROZEN_REPLY => f.pad("BR_FROZEN_REPLY"),
+            BR_TRANSACTION_PENDING_FROZEN => f.pad("BR_TRANSACTION_PENDING_FROZEN"),
+            BR_TRANSACTION_COMPLETE => f.pad("BR_TRANSACTION_COMPLETE"),
+            _ => f
+                .debug_struct("BinderError")
+                .field("reply", &self.reply)
+                .finish(),
+        }
+    }
+}

drivers/android/binder/freeze.rs

@@ -0,0 +1,388 @@
+// SPDX-License-Identifier: GPL-2.0
+
+// Copyright (C) 2025 Google LLC.
+
+use kernel::{
+    alloc::AllocError,
+    list::ListArc,
+    prelude::*,
+    rbtree::{self, RBTreeNodeReservation},
+    seq_file::SeqFile,
+    seq_print,
+    sync::{Arc, UniqueArc},
+    uaccess::UserSliceReader,
+};
+
+use crate::{
+    defs::*, node::Node, process::Process, thread::Thread, BinderReturnWriter, DArc, DLArc,
+    DTRWrap, DeliverToRead,
+};
+
+#[derive(Clone, Copy, Eq, PartialEq, Ord, PartialOrd)]
+pub(crate) struct FreezeCookie(u64);
+
+/// Represents a listener for changes to the frozen state of a process.
+pub(crate) struct FreezeListener {
+    /// The node we are listening for.
+    pub(crate) node: DArc<Node>,
+    /// The cookie of this freeze listener.
+    cookie: FreezeCookie,
+    /// What value of `is_frozen` did we most recently tell userspace about?
+    last_is_frozen: Option<bool>,
+    /// We sent a `BR_FROZEN_BINDER` and we are waiting for `BC_FREEZE_NOTIFICATION_DONE` before
+    /// sending any other commands.
+    is_pending: bool,
+    /// Userspace sent `BC_CLEAR_FREEZE_NOTIFICATION` and we need to reply with
+    /// `BR_CLEAR_FREEZE_NOTIFICATION_DONE` as soon as possible. If `is_pending` is set, then we
+    /// must wait for it to be unset before we can reply.
+    is_clearing: bool,
+    /// Number of cleared duplicates that can't be deleted until userspace sends
+    /// `BC_FREEZE_NOTIFICATION_DONE`.
+    num_pending_duplicates: u64,
+    /// Number of cleared duplicates that can be deleted.
+    num_cleared_duplicates: u64,
+}
+
+impl FreezeListener {
+    /// Is it okay to create a new listener with the same cookie as this one for the provided node?
+    ///
+    /// Under some scenarios, userspace may delete a freeze listener and immediately recreate it
+    /// with the same cookie. This results in duplicate listeners. To avoid issues with ambiguity,
+    /// we allow this only if the new listener is for the same node, and we also require that the
+    /// old listener has already been cleared.
+    fn allow_duplicate(&self, node: &DArc<Node>) -> bool {
+        Arc::ptr_eq(&self.node, node) && self.is_clearing
+    }
+}
+
+type UninitFM = UniqueArc<core::mem::MaybeUninit<DTRWrap<FreezeMessage>>>;
+
+/// Represents a notification that the freeze state has changed.
+pub(crate) struct FreezeMessage {
+    cookie: FreezeCookie,
+}
+
+kernel::list::impl_list_arc_safe! {
+    impl ListArcSafe<0> for FreezeMessage {
+        untracked;
+    }
+}
+
+impl FreezeMessage {
+    fn new(flags: kernel::alloc::Flags) -> Result<UninitFM, AllocError> {
+        UniqueArc::new_uninit(flags)
+    }
+
+    fn init(ua: UninitFM, cookie: FreezeCookie) -> DLArc<FreezeMessage> {
+        match ua.pin_init_with(DTRWrap::new(FreezeMessage { cookie })) {
+            Ok(msg) => ListArc::from(msg),
+            Err(err) => match err {},
+        }
+    }
+}
+
+impl DeliverToRead for FreezeMessage {
+    fn do_work(
+        self: DArc<Self>,
+        thread: &Thread,
+        writer: &mut BinderReturnWriter<'_>,
+    ) -> Result<bool> {
+        let _removed_listener;
+        let mut node_refs = thread.process.node_refs.lock();
+        let Some(mut freeze_entry) = node_refs.freeze_listeners.find_mut(&self.cookie) else {
+            return Ok(true);
+        };
+        let freeze = freeze_entry.get_mut();
+
+        if freeze.num_cleared_duplicates > 0 {
+            freeze.num_cleared_duplicates -= 1;
+            drop(node_refs);
+            writer.write_code(BR_CLEAR_FREEZE_NOTIFICATION_DONE)?;
+            writer.write_payload(&self.cookie.0)?;
+            return Ok(true);
+        }
+
+        if freeze.is_pending {
+            return Ok(true);
+        }
+        if freeze.is_clearing {
+            _removed_listener = freeze_entry.remove_node();
+            drop(node_refs);
+            writer.write_code(BR_CLEAR_FREEZE_NOTIFICATION_DONE)?;
+            writer.write_payload(&self.cookie.0)?;
+            Ok(true)
+        } else {
+            let is_frozen = freeze.node.owner.inner.lock().is_frozen;
+            if freeze.last_is_frozen == Some(is_frozen) {
+                return Ok(true);
+            }
+
+            let mut state_info = BinderFrozenStateInfo::default();
+            state_info.is_frozen = is_frozen as u32;
+            state_info.cookie = freeze.cookie.0;
+            freeze.is_pending = true;
+            freeze.last_is_frozen = Some(is_frozen);
+            drop(node_refs);
+
+            writer.write_code(BR_FROZEN_BINDER)?;
+            writer.write_payload(&state_info)?;
+            // BR_FROZEN_BINDER notifications can cause transactions
+            Ok(false)
+        }
+    }
+
+    fn cancel(self: DArc<Self>) {}
+
+    fn should_sync_wakeup(&self) -> bool {
+        false
+    }
+
+    #[inline(never)]
+    fn debug_print(&self, m: &SeqFile, prefix: &str, _tprefix: &str) -> Result<()> {
+        seq_print!(m, "{}has frozen binder\n", prefix);
+        Ok(())
+    }
+}
+
+impl FreezeListener {
+    pub(crate) fn on_process_exit(&self, proc: &Arc<Process>) {
+        if !self.is_clearing {
+            self.node.remove_freeze_listener(proc);
+        }
+    }
+}
+
+impl Process {
+    pub(crate) fn request_freeze_notif(
+        self: &Arc<Self>,
+        reader: &mut UserSliceReader,
+    ) -> Result<()> {
+        let hc = reader.read::<BinderHandleCookie>()?;
+        let handle = hc.handle;
+        let cookie = FreezeCookie(hc.cookie);
+
+        let msg = FreezeMessage::new(GFP_KERNEL)?;
+        let alloc = RBTreeNodeReservation::new(GFP_KERNEL)?;
+
+        let mut node_refs_guard = self.node_refs.lock();
+        let node_refs = &mut *node_refs_guard;
+        let Some(info) = node_refs.by_handle.get_mut(&handle) else {
+            pr_warn!("BC_REQUEST_FREEZE_NOTIFICATION invalid ref {}\n", handle);
+            return Err(EINVAL);
+        };
+        if info.freeze().is_some() {
+            pr_warn!("BC_REQUEST_FREEZE_NOTIFICATION already set\n");
+            return Err(EINVAL);
+        }
+        let node_ref = info.node_ref();
+        let freeze_entry = node_refs.freeze_listeners.entry(cookie);
+
+        if let rbtree::Entry::Occupied(ref dupe) = freeze_entry {
+            if !dupe.get().allow_duplicate(&node_ref.node) {
+                pr_warn!("BC_REQUEST_FREEZE_NOTIFICATION duplicate cookie\n");
+                return Err(EINVAL);
+            }
+        }
+
+        // All failure paths must come before this call, and all modifications must come after this
+        // call.
+        node_ref.node.add_freeze_listener(self, GFP_KERNEL)?;
+
+        match freeze_entry {
+            rbtree::Entry::Vacant(entry) => {
+                entry.insert(
+                    FreezeListener {
+                        cookie,
+                        node: node_ref.node.clone(),
+                        last_is_frozen: None,
+                        is_pending: false,
+                        is_clearing: false,
+                        num_pending_duplicates: 0,
+                        num_cleared_duplicates: 0,
+                    },
+                    alloc,
+                );
+            }
+            rbtree::Entry::Occupied(mut dupe) => {
+                let dupe = dupe.get_mut();
+                if dupe.is_pending {
+                    dupe.num_pending_duplicates += 1;
+                } else {
+                    dupe.num_cleared_duplicates += 1;
+                }
+                dupe.last_is_frozen = None;
+                dupe.is_pending = false;
+                dupe.is_clearing = false;
+            }
+        }
+
+        *info.freeze() = Some(cookie);
+        let msg = FreezeMessage::init(msg, cookie);
+        drop(node_refs_guard);
+        let _ = self.push_work(msg);
+        Ok(())
+    }
+
+    pub(crate) fn freeze_notif_done(self: &Arc<Self>, reader: &mut UserSliceReader) -> Result<()> {
+        let cookie = FreezeCookie(reader.read()?);
+        let alloc = FreezeMessage::new(GFP_KERNEL)?;
+        let mut node_refs_guard = self.node_refs.lock();
+        let node_refs = &mut *node_refs_guard;
+        let Some(freeze) = node_refs.freeze_listeners.get_mut(&cookie) else {
+            pr_warn!("BC_FREEZE_NOTIFICATION_DONE {:016x} not found\n", cookie.0);
+            return Err(EINVAL);
+        };
+        let mut clear_msg = None;
+        if freeze.num_pending_duplicates > 0 {
+            clear_msg = Some(FreezeMessage::init(alloc, cookie));
+            freeze.num_pending_duplicates -= 1;
+            freeze.num_cleared_duplicates += 1;
+        } else {
+            if !freeze.is_pending {
+                pr_warn!(
+                    "BC_FREEZE_NOTIFICATION_DONE {:016x} not pending\n",
+                    cookie.0
+                );
+                return Err(EINVAL);
+            }
+            if freeze.is_clearing {
+                // Immediately send another FreezeMessage for BR_CLEAR_FREEZE_NOTIFICATION_DONE.
+                clear_msg = Some(FreezeMessage::init(alloc, cookie));
+            }
+            freeze.is_pending = false;
+        }
+        drop(node_refs_guard);
+        if let Some(clear_msg) = clear_msg {
+            let _ = self.push_work(clear_msg);
+        }
+        Ok(())
+    }
+
+    pub(crate) fn clear_freeze_notif(self: &Arc<Self>, reader: &mut UserSliceReader) -> Result<()> {
+        let hc = reader.read::<BinderHandleCookie>()?;
+        let handle = hc.handle;
+        let cookie = FreezeCookie(hc.cookie);
+
+        let alloc = FreezeMessage::new(GFP_KERNEL)?;
+        let mut node_refs_guard = self.node_refs.lock();
+        let node_refs = &mut *node_refs_guard;
+        let Some(info) = node_refs.by_handle.get_mut(&handle) else {
+            pr_warn!("BC_CLEAR_FREEZE_NOTIFICATION invalid ref {}\n", handle);
+            return Err(EINVAL);
+        };
+        let Some(info_cookie) = info.freeze() else {
+            pr_warn!("BC_CLEAR_FREEZE_NOTIFICATION freeze notification not active\n");
+            return Err(EINVAL);
+        };
+        if *info_cookie != cookie {
+            pr_warn!("BC_CLEAR_FREEZE_NOTIFICATION freeze notification cookie mismatch\n");
+            return Err(EINVAL);
+        }
+        let Some(listener) = node_refs.freeze_listeners.get_mut(&cookie) else {
+            pr_warn!("BC_CLEAR_FREEZE_NOTIFICATION invalid cookie {}\n", handle);
+            return Err(EINVAL);
+        };
+        listener.is_clearing = true;
+        listener.node.remove_freeze_listener(self);
+        *info.freeze() = None;
+        let mut msg = None;
+        if !listener.is_pending {
+            msg = Some(FreezeMessage::init(alloc, cookie));
+        }
+        drop(node_refs_guard);
+
+        if let Some(msg) = msg {
+            let _ = self.push_work(msg);
+        }
+        Ok(())
+    }
+
+    fn get_freeze_cookie(&self, node: &DArc<Node>) -> Option<FreezeCookie> {
+        let node_refs = &mut *self.node_refs.lock();
+        let handle = node_refs.by_node.get(&node.global_id())?;
+        let node_ref = node_refs.by_handle.get_mut(handle)?;
+        *node_ref.freeze()
+    }
+
+    /// Creates a vector of every freeze listener on this process.
+    ///
+    /// Returns pairs of the remote process listening for notifications and the local node it is
+    /// listening on.
+    #[expect(clippy::type_complexity)]
+    fn find_freeze_recipients(&self) -> Result<KVVec<(DArc<Node>, Arc<Process>)>, AllocError> {
+        // Defined before `inner` to drop after releasing spinlock if `push_within_capacity` fails.
+        let mut node_proc_pair;
+
+        // We pre-allocate space for up to 8 recipients before we take the spinlock. However, if
+        // the allocation fails, use a vector with a capacity of zero instead of failing. After
+        // all, there might not be any freeze listeners, in which case this operation could still
+        // succeed.
+        let mut recipients =
+            KVVec::with_capacity(8, GFP_KERNEL).unwrap_or_else(|_err| KVVec::new());
+
+        let mut inner = self.lock_with_nodes();
+        let mut curr = inner.nodes.cursor_front();
+        while let Some(cursor) = curr {
+            let (key, node) = cursor.current();
+            let key = *key;
+            let list = node.freeze_list(&inner.inner);
+            let len = list.len();
+
+            if recipients.spare_capacity_mut().len() < len {
+                drop(inner);
+                recipients.reserve(len, GFP_KERNEL)?;
+                inner = self.lock_with_nodes();
+                // Find the node we were looking at and try again. If the set of nodes was changed,
+                // then just proceed to the next node. This is ok because we don't guarantee the
+                // inclusion of nodes that are added or removed in parallel with this operation.
+                curr = inner.nodes.cursor_lower_bound(&key);
+                continue;
+            }
+
+            for proc in list {
+                node_proc_pair = (node.clone(), proc.clone());
+                recipients
+                    .push_within_capacity(node_proc_pair)
+                    .map_err(|_| {
+                        pr_err!(
+                            "push_within_capacity failed even though we checked the capacity\n"
+                        );
+                        AllocError
+                    })?;
+            }
+
+            curr = cursor.move_next();
+        }
+        Ok(recipients)
+    }
+
+    /// Prepare allocations for sending freeze messages.
+    pub(crate) fn prepare_freeze_messages(&self) -> Result<FreezeMessages, AllocError> {
+        let recipients = self.find_freeze_recipients()?;
+        let mut batch = KVVec::with_capacity(recipients.len(), GFP_KERNEL)?;
+        for (node, proc) in recipients {
+            let Some(cookie) = proc.get_freeze_cookie(&node) else {
+                // If the freeze listener was removed in the meantime, just discard the
+                // notification.
+                continue;
+            };
+            let msg_alloc = FreezeMessage::new(GFP_KERNEL)?;
+            let msg = FreezeMessage::init(msg_alloc, cookie);
+            batch.push((proc, msg), GFP_KERNEL)?;
+        }
+
+        Ok(FreezeMessages { batch })
+    }
+}
+
+pub(crate) struct FreezeMessages {
+    batch: KVVec<(Arc<Process>, DLArc<FreezeMessage>)>,
+}
+
+impl FreezeMessages {
+    pub(crate) fn send_messages(self) {
+        for (proc, msg) in self.batch {
+            let _ = proc.push_work(msg);
+        }
+    }
+}

drivers/android/binder/node/wrapper.rs

@@ -0,0 +1,78 @@
+// SPDX-License-Identifier: GPL-2.0
+
+// Copyright (C) 2025 Google LLC.
+
+use kernel::{list::ListArc, prelude::*, seq_file::SeqFile, seq_print, sync::UniqueArc};
+
+use crate::{node::Node, thread::Thread, BinderReturnWriter, DArc, DLArc, DTRWrap, DeliverToRead};
+
+use core::mem::MaybeUninit;
+
+pub(crate) struct CritIncrWrapper {
+    inner: UniqueArc<MaybeUninit<DTRWrap<NodeWrapper>>>,
+}
+
+impl CritIncrWrapper {
+    pub(crate) fn new() -> Result<Self> {
+        Ok(CritIncrWrapper {
+            inner: UniqueArc::new_uninit(GFP_KERNEL)?,
+        })
+    }
+
+    pub(super) fn init(self, node: DArc<Node>) -> DLArc<dyn DeliverToRead> {
+        match self.inner.pin_init_with(DTRWrap::new(NodeWrapper { node })) {
+            Ok(initialized) => ListArc::from(initialized) as _,
+            Err(err) => match err {},
+        }
+    }
+}
+
+struct NodeWrapper {
+    node: DArc<Node>,
+}
+
+kernel::list::impl_list_arc_safe! {
+    impl ListArcSafe<0> for NodeWrapper {
+        untracked;
+    }
+}
+
+impl DeliverToRead for NodeWrapper {
+    fn do_work(
+        self: DArc<Self>,
+        _thread: &Thread,
+        writer: &mut BinderReturnWriter<'_>,
+    ) -> Result<bool> {
+        let node = &self.node;
+        let mut owner_inner = node.owner.inner.lock();
+        let inner = node.inner.access_mut(&mut owner_inner);
+
+        let ds = &mut inner.delivery_state;
+
+        assert!(ds.has_pushed_wrapper);
+        assert!(ds.has_strong_zero2one);
+        ds.has_pushed_wrapper = false;
+        ds.has_strong_zero2one = false;
+
+        node.do_work_locked(writer, owner_inner)
+    }
+
+    fn cancel(self: DArc<Self>) {}
+
+    fn should_sync_wakeup(&self) -> bool {
+        false
+    }
+
+    #[inline(never)]
+    fn debug_print(&self, m: &SeqFile, prefix: &str, _tprefix: &str) -> Result<()> {
+        seq_print!(
+            m,
+            "{}node work {}: u{:016x} c{:016x}\n",
+            prefix,
+            self.node.debug_id,
+            self.node.ptr,
+            self.node.cookie,
+        );
+        Ok(())
+    }
+}

drivers/android/binder/page_range.rs

@@ -0,0 +1,734 @@
+// SPDX-License-Identifier: GPL-2.0
+
+// Copyright (C) 2025 Google LLC.
+
+//! This module has utilities for managing a page range where unused pages may be reclaimed by a
+//! vma shrinker.
+
+// To avoid deadlocks, locks are taken in the order:
+//
+//  1. mmap lock
+//  2. spinlock
+//  3. lru spinlock
+//
+// The shrinker will use trylock methods because it locks them in a different order.
+
+use core::{
+    marker::PhantomPinned,
+    mem::{size_of, size_of_val, MaybeUninit},
+    ptr,
+};
+
+use kernel::{
+    bindings,
+    error::Result,
+    ffi::{c_ulong, c_void},
+    mm::{virt, Mm, MmWithUser},
+    new_mutex, new_spinlock,
+    page::{Page, PAGE_SHIFT, PAGE_SIZE},
+    prelude::*,
+    str::CStr,
+    sync::{aref::ARef, Mutex, SpinLock},
+    task::Pid,
+    transmute::FromBytes,
+    types::Opaque,
+    uaccess::UserSliceReader,
+};
+
+/// Represents a shrinker that can be registered with the kernel.
+///
+/// Each shrinker can be used by many `ShrinkablePageRange` objects.
+#[repr(C)]
+pub(crate) struct Shrinker {
+    inner: Opaque<*mut bindings::shrinker>,
+    list_lru: Opaque<bindings::list_lru>,
+}
+
+// SAFETY: The shrinker and list_lru are thread safe.
+unsafe impl Send for Shrinker {}
+// SAFETY: The shrinker and list_lru are thread safe.
+unsafe impl Sync for Shrinker {}
+
+impl Shrinker {
+    /// Create a new shrinker.
+    ///
+    /// # Safety
+    ///
+    /// Before using this shrinker with a `ShrinkablePageRange`, the `register` method must have
+    /// been called exactly once, and it must not have returned an error.
+    pub(crate) const unsafe fn new() -> Self {
+        Self {
+            inner: Opaque::uninit(),
+            list_lru: Opaque::uninit(),
+        }
+    }
+
+    /// Register this shrinker with the kernel.
+    pub(crate) fn register(&'static self, name: &CStr) -> Result<()> {
+        // SAFETY: These fields are not yet used, so it's okay to zero them.
+        unsafe {
+            self.inner.get().write(ptr::null_mut());
+            self.list_lru.get().write_bytes(0, 1);
+        }
+
+        // SAFETY: The field is not yet used, so we can initialize it.
+        let ret = unsafe { bindings::__list_lru_init(self.list_lru.get(), false, ptr::null_mut()) };
+        if ret != 0 {
+            return Err(Error::from_errno(ret));
+        }
+
+        // SAFETY: The `name` points at a valid c string.
+        let shrinker = unsafe { bindings::shrinker_alloc(0, name.as_char_ptr()) };
+        if shrinker.is_null() {
+            // SAFETY: We initialized it, so its okay to destroy it.
+            unsafe { bindings::list_lru_destroy(self.list_lru.get()) };
+            return Err(Error::from_errno(ret));
+        }
+
+        // SAFETY: We're about to register the shrinker, and these are the fields we need to
+        // initialize. (All other fields are already zeroed.)
+        unsafe {
+            (&raw mut (*shrinker).count_objects).write(Some(rust_shrink_count));
+            (&raw mut (*shrinker).scan_objects).write(Some(rust_shrink_scan));
+            (&raw mut (*shrinker).private_data).write(self.list_lru.get().cast());
+        }
+
+        // SAFETY: The new shrinker has been fully initialized, so we can register it.
+        unsafe { bindings::shrinker_register(shrinker) };
+
+        // SAFETY: This initializes the pointer to the shrinker so that we can use it.
+        unsafe { self.inner.get().write(shrinker) };
+
+        Ok(())
+    }
+}
+
+/// A container that manages a page range in a vma.
+///
+/// The pages can be thought of as an array of booleans of whether the pages are usable. The
+/// methods `use_range` and `stop_using_range` set all booleans in a range to true or false
+/// respectively. Initially, no pages are allocated. When a page is not used, it is not freed
+/// immediately. Instead, it is made available to the memory shrinker to free it if the device is
+/// under memory pressure.
+///
+/// It's okay for `use_range` and `stop_using_range` to race with each other, although there's no
+/// way to know whether an index ends up with true or false if a call to `use_range` races with
+/// another call to `stop_using_range` on a given index.
+///
+/// It's also okay for the two methods to race with themselves, e.g. if two threads call
+/// `use_range` on the same index, then that's fine and neither call will return until the page is
+/// allocated and mapped.
+///
+/// The methods that read or write to a range require that the page is marked as in use. So it is
+/// _not_ okay to call `stop_using_range` on a page that is in use by the methods that read or
+/// write to the page.
+#[pin_data(PinnedDrop)]
+pub(crate) struct ShrinkablePageRange {
+    /// Shrinker object registered with the kernel.
+    shrinker: &'static Shrinker,
+    /// Pid using this page range. Only used as debugging information.
+    pid: Pid,
+    /// The mm for the relevant process.
+    mm: ARef<Mm>,
+    /// Used to synchronize calls to `vm_insert_page` and `zap_page_range_single`.
+    #[pin]
+    mm_lock: Mutex<()>,
+    /// Spinlock protecting changes to pages.
+    #[pin]
+    lock: SpinLock<Inner>,
+
+    /// Must not move, since page info has pointers back.
+    #[pin]
+    _pin: PhantomPinned,
+}
+
+struct Inner {
+    /// Array of pages.
+    ///
+    /// Since this is also accessed by the shrinker, we can't use a `Box`, which asserts exclusive
+    /// ownership. To deal with that, we manage it using raw pointers.
+    pages: *mut PageInfo,
+    /// Length of the `pages` array.
+    size: usize,
+    /// The address of the vma to insert the pages into.
+    vma_addr: usize,
+}
+
+// SAFETY: proper locking is in place for `Inner`
+unsafe impl Send for Inner {}
+
+type StableMmGuard =
+    kernel::sync::lock::Guard<'static, (), kernel::sync::lock::mutex::MutexBackend>;
+
+/// An array element that describes the current state of a page.
+///
+/// There are three states:
+///
+///  * Free. The page is None. The `lru` element is not queued.
+///  * Available. The page is Some. The `lru` element is queued to the shrinker's lru.
+///  * Used. The page is Some. The `lru` element is not queued.
+///
+/// When an element is available, the shrinker is able to free the page.
+#[repr(C)]
+struct PageInfo {
+    lru: bindings::list_head,
+    page: Option<Page>,
+    range: *const ShrinkablePageRange,
+}
+
+impl PageInfo {
+    /// # Safety
+    ///
+    /// The caller ensures that writing to `me.page` is ok, and that the page is not currently set.
+    unsafe fn set_page(me: *mut PageInfo, page: Page) {
+        // SAFETY: This pointer offset is in bounds.
+        let ptr = unsafe { &raw mut (*me).page };
+
+        // SAFETY: The pointer is valid for writing, so also valid for reading.
+        if unsafe { (*ptr).is_some() } {
+            pr_err!("set_page called when there is already a page");
+            // SAFETY: We will initialize the page again below.
+            unsafe { ptr::drop_in_place(ptr) };
+        }
+
+        // SAFETY: The pointer is valid for writing.
+        unsafe { ptr::write(ptr, Some(page)) };
+    }
+
+    /// # Safety
+    ///
+    /// The caller ensures that reading from `me.page` is ok for the duration of 'a.
+    unsafe fn get_page<'a>(me: *const PageInfo) -> Option<&'a Page> {
+        // SAFETY: This pointer offset is in bounds.
+        let ptr = unsafe { &raw const (*me).page };
+
+        // SAFETY: The pointer is valid for reading.
+        unsafe { (*ptr).as_ref() }
+    }
+
+    /// # Safety
+    ///
+    /// The caller ensures that writing to `me.page` is ok for the duration of 'a.
+    unsafe fn take_page(me: *mut PageInfo) -> Option<Page> {
+        // SAFETY: This pointer offset is in bounds.
+        let ptr = unsafe { &raw mut (*me).page };
+
+        // SAFETY: The pointer is valid for reading.
+        unsafe { (*ptr).take() }
+    }
+
+    /// Add this page to the lru list, if not already in the list.
+    ///
+    /// # Safety
+    ///
+    /// The pointer must be valid, and it must be the right shrinker and nid.
+    unsafe fn list_lru_add(me: *mut PageInfo, nid: i32, shrinker: &'static Shrinker) {
+        // SAFETY: This pointer offset is in bounds.
+        let lru_ptr = unsafe { &raw mut (*me).lru };
+        // SAFETY: The lru pointer is valid, and we're not using it with any other lru list.
+        unsafe { bindings::list_lru_add(shrinker.list_lru.get(), lru_ptr, nid, ptr::null_mut()) };
+    }
+
+    /// Remove this page from the lru list, if it is in the list.
+    ///
+    /// # Safety
+    ///
+    /// The pointer must be valid, and it must be the right shrinker and nid.
+    unsafe fn list_lru_del(me: *mut PageInfo, nid: i32, shrinker: &'static Shrinker) {
+        // SAFETY: This pointer offset is in bounds.
+        let lru_ptr = unsafe { &raw mut (*me).lru };
+        // SAFETY: The lru pointer is valid, and we're not using it with any other lru list.
+        unsafe { bindings::list_lru_del(shrinker.list_lru.get(), lru_ptr, nid, ptr::null_mut()) };
+    }
+}
+
+impl ShrinkablePageRange {
+    /// Create a new `ShrinkablePageRange` using the given shrinker.
+    pub(crate) fn new(shrinker: &'static Shrinker) -> impl PinInit<Self, Error> {
+        try_pin_init!(Self {
+            shrinker,
+            pid: kernel::current!().pid(),
+            mm: ARef::from(&**kernel::current!().mm().ok_or(ESRCH)?),
+            mm_lock <- new_mutex!((), "ShrinkablePageRange::mm"),
+            lock <- new_spinlock!(Inner {
+                pages: ptr::null_mut(),
+                size: 0,
+                vma_addr: 0,
+            }, "ShrinkablePageRange"),
+            _pin: PhantomPinned,
+        })
+    }
+
+    pub(crate) fn stable_trylock_mm(&self) -> Option<StableMmGuard> {
+        // SAFETY: This extends the duration of the reference. Since this call happens before
+        // `mm_lock` is taken in the destructor of `ShrinkablePageRange`, the destructor will block
+        // until the returned guard is dropped. This ensures that the guard is valid until dropped.
+        let mm_lock = unsafe { &*ptr::from_ref(&self.mm_lock) };
+
+        mm_lock.try_lock()
+    }
+
+    /// Register a vma with this page range. Returns the size of the region.
+    pub(crate) fn register_with_vma(&self, vma: &virt::VmaNew) -> Result<usize> {
+        let num_bytes = usize::min(vma.end() - vma.start(), bindings::SZ_4M as usize);
+        let num_pages = num_bytes >> PAGE_SHIFT;
+
+        if !ptr::eq::<Mm>(&*self.mm, &**vma.mm()) {
+            pr_debug!("Failed to register with vma: invalid vma->vm_mm");
+            return Err(EINVAL);
+        }
+        if num_pages == 0 {
+            pr_debug!("Failed to register with vma: size zero");
+            return Err(EINVAL);
+        }
+
+        let mut pages = KVVec::<PageInfo>::with_capacity(num_pages, GFP_KERNEL)?;
+
+        // SAFETY: This just initializes the pages array.
+        unsafe {
+            let self_ptr = self as *const ShrinkablePageRange;
+            for i in 0..num_pages {
+                let info = pages.as_mut_ptr().add(i);
+                (&raw mut (*info).range).write(self_ptr);
+                (&raw mut (*info).page).write(None);
+                let lru = &raw mut (*info).lru;
+                (&raw mut (*lru).next).write(lru);
+                (&raw mut (*lru).prev).write(lru);
+            }
+        }
+
+        let mut inner = self.lock.lock();
+        if inner.size > 0 {
+            pr_debug!("Failed to register with vma: already registered");
+            drop(inner);
+            return Err(EBUSY);
+        }
+
+        inner.pages = pages.into_raw_parts().0;
+        inner.size = num_pages;
+        inner.vma_addr = vma.start();
+
+        Ok(num_pages)
+    }
+
+    /// Make sure that the given pages are allocated and mapped.
+    ///
+    /// Must not be called from an atomic context.
+    pub(crate) fn use_range(&self, start: usize, end: usize) -> Result<()> {
+        if start >= end {
+            return Ok(());
+        }
+        let mut inner = self.lock.lock();
+        assert!(end <= inner.size);
+
+        for i in start..end {
+            // SAFETY: This pointer offset is in bounds.
+            let page_info = unsafe { inner.pages.add(i) };
+
+            // SAFETY: The pointer is valid, and we hold the lock so reading from the page is okay.
+            if let Some(page) = unsafe { PageInfo::get_page(page_info) } {
+                // Since we're going to use the page, we should remove it from the lru list so that
+                // the shrinker will not free it.
+                //
+                // SAFETY: The pointer is valid, and this is the right shrinker.
+                //
+                // The shrinker can't free the page between the check and this call to
+                // `list_lru_del` because we hold the lock.
+                unsafe { PageInfo::list_lru_del(page_info, page.nid(), self.shrinker) };
+            } else {
+                // We have to allocate a new page. Use the slow path.
+                drop(inner);
+                // SAFETY: `i < end <= inner.size` so `i` is in bounds.
+                match unsafe { self.use_page_slow(i) } {
+                    Ok(()) => {}
+                    Err(err) => {
+                        pr_warn!("Error in use_page_slow: {:?}", err);
+                        return Err(err);
+                    }
+                }
+                inner = self.lock.lock();
+            }
+        }
+        Ok(())
+    }
+
+    /// Mark the given page as in use, slow path.
+    ///
+    /// Must not be called from an atomic context.
+    ///
+    /// # Safety
+    ///
+    /// Assumes that `i` is in bounds.
+    #[cold]
+    unsafe fn use_page_slow(&self, i: usize) -> Result<()> {
+        let new_page = Page::alloc_page(GFP_KERNEL | __GFP_HIGHMEM | __GFP_ZERO)?;
+
+        let mm_mutex = self.mm_lock.lock();
+        let inner = self.lock.lock();
+
+        // SAFETY: This pointer offset is in bounds.
+        let page_info = unsafe { inner.pages.add(i) };
+
+        // SAFETY: The pointer is valid, and we hold the lock so reading from the page is okay.
+        if let Some(page) = unsafe { PageInfo::get_page(page_info) } {
+            // The page was already there, or someone else added the page while we didn't hold the
+            // spinlock.
+            //
+            // SAFETY: The pointer is valid, and this is the right shrinker.
+            //
+            // The shrinker can't free the page between the check and this call to
+            // `list_lru_del` because we hold the lock.
+            unsafe { PageInfo::list_lru_del(page_info, page.nid(), self.shrinker) };
+            return Ok(());
+        }
+
+        let vma_addr = inner.vma_addr;
+        // Release the spinlock while we insert the page into the vma.
+        drop(inner);
+
+        // No overflow since we stay in bounds of the vma.
+        let user_page_addr = vma_addr + (i << PAGE_SHIFT);
+
+        // We use `mmput_async` when dropping the `mm` because `use_page_slow` is usually used from
+        // a remote process. If the call to `mmput` races with the process shutting down, then the
+        // caller of `use_page_slow` becomes responsible for cleaning up the `mm`, which doesn't
+        // happen until it returns to userspace. However, the caller might instead go to sleep and
+        // wait for the owner of the `mm` to wake it up, which doesn't happen because it's in the
+        // middle of a shutdown process that won't complete until the `mm` is dropped. This can
+        // amount to a deadlock.
+        //
+        // Using `mmput_async` avoids this, because then the `mm` cleanup is instead queued to a
+        // workqueue.
+        MmWithUser::into_mmput_async(self.mm.mmget_not_zero().ok_or(ESRCH)?)
+            .mmap_read_lock()
+            .vma_lookup(vma_addr)
+            .ok_or(ESRCH)?
+            .as_mixedmap_vma()
+            .ok_or(ESRCH)?
+            .vm_insert_page(user_page_addr, &new_page)
+            .inspect_err(|err| {
+                pr_warn!(
+                    "Failed to vm_insert_page({}): vma_addr:{} i:{} err:{:?}",
+                    user_page_addr,
+                    vma_addr,
+                    i,
+                    err
+                )
+            })?;
+
+        let inner = self.lock.lock();
+
+        // SAFETY: The `page_info` pointer is valid and currently does not have a page. The page
+        // can be written to since we hold the lock.
+        //
+        // We released and reacquired the spinlock since we checked that the page is null, but we
+        // always hold the mm_lock mutex when setting the page to a non-null value, so it's not
+        // possible for someone else to have changed it since our check.
+        unsafe { PageInfo::set_page(page_info, new_page) };
+
+        drop(inner);
+        drop(mm_mutex);
+
+        Ok(())
+    }
+
+    /// If the given page is in use, then mark it as available so that the shrinker can free it.
+    ///
+    /// May be called from an atomic context.
+    pub(crate) fn stop_using_range(&self, start: usize, end: usize) {
+        if start >= end {
+            return;
+        }
+        let inner = self.lock.lock();
+        assert!(end <= inner.size);
+
+        for i in (start..end).rev() {
+            // SAFETY: The pointer is in bounds.
+            let page_info = unsafe { inner.pages.add(i) };
+
+            // SAFETY: Okay for reading since we have the lock.
+            if let Some(page) = unsafe { PageInfo::get_page(page_info) } {
+                // SAFETY: The pointer is valid, and it's the right shrinker.
+                unsafe { PageInfo::list_lru_add(page_info, page.nid(), self.shrinker) };
+            }
+        }
+    }
+
+    /// Helper for reading or writing to a range of bytes that may overlap with several pages.
+    ///
+    /// # Safety
+    ///
+    /// All pages touched by this operation must be in use for the duration of this call.
+    unsafe fn iterate<T>(&self, mut offset: usize, mut size: usize, mut cb: T) -> Result
+    where
+        T: FnMut(&Page, usize, usize) -> Result,
+    {
+        if size == 0 {
+            return Ok(());
+        }
+
+        let (pages, num_pages) = {
+            let inner = self.lock.lock();
+            (inner.pages, inner.size)
+        };
+        let num_bytes = num_pages << PAGE_SHIFT;
+
+        // Check that the request is within the buffer.
+        if offset.checked_add(size).ok_or(EFAULT)? > num_bytes {
+            return Err(EFAULT);
+        }
+
+        let mut page_index = offset >> PAGE_SHIFT;
+        offset &= PAGE_SIZE - 1;
+        while size > 0 {
+            let available = usize::min(size, PAGE_SIZE - offset);
+            // SAFETY: The pointer is in bounds.
+            let page_info = unsafe { pages.add(page_index) };
+            // SAFETY: The caller guarantees that this page is in the "in use" state for the
+            // duration of this call to `iterate`, so nobody will change the page.
+            let page = unsafe { PageInfo::get_page(page_info) };
+            if page.is_none() {
+                pr_warn!("Page is null!");
+            }
+            let page = page.ok_or(EFAULT)?;
+            cb(page, offset, available)?;
+            size -= available;
+            page_index += 1;
+            offset = 0;
+        }
+        Ok(())
+    }
+
+    /// Copy from userspace into this page range.
+    ///
+    /// # Safety
+    ///
+    /// All pages touched by this operation must be in use for the duration of this call.
+    pub(crate) unsafe fn copy_from_user_slice(
+        &self,
+        reader: &mut UserSliceReader,
+        offset: usize,
+        size: usize,
+    ) -> Result {
+        // SAFETY: `self.iterate` has the same safety requirements as `copy_from_user_slice`.
+        unsafe {
+            self.iterate(offset, size, |page, offset, to_copy| {
+                page.copy_from_user_slice_raw(reader, offset, to_copy)
+            })
+        }
+    }
+
+    /// Copy from this page range into kernel space.
+    ///
+    /// # Safety
+    ///
+    /// All pages touched by this operation must be in use for the duration of this call.
+    pub(crate) unsafe fn read<T: FromBytes>(&self, offset: usize) -> Result<T> {
+        let mut out = MaybeUninit::<T>::uninit();
+        let mut out_offset = 0;
+        // SAFETY: `self.iterate` has the same safety requirements as `read`.
+        unsafe {
+            self.iterate(offset, size_of::<T>(), |page, offset, to_copy| {
+                // SAFETY: The sum of `offset` and `to_copy` is bounded by the size of T.
+                let obj_ptr = (out.as_mut_ptr() as *mut u8).add(out_offset);
+                // SAFETY: The pointer points is in-bounds of the `out` variable, so it is valid.
+                page.read_raw(obj_ptr, offset, to_copy)?;
+                out_offset += to_copy;
+                Ok(())
+            })?;
+        }
+        // SAFETY: We just initialised the data.
+        Ok(unsafe { out.assume_init() })
+    }
+
+    /// Copy from kernel space into this page range.
+    ///
+    /// # Safety
+    ///
+    /// All pages touched by this operation must be in use for the duration of this call.
+    pub(crate) unsafe fn write<T: ?Sized>(&self, offset: usize, obj: &T) -> Result {
+        let mut obj_offset = 0;
+        // SAFETY: `self.iterate` has the same safety requirements as `write`.
+        unsafe {
+            self.iterate(offset, size_of_val(obj), |page, offset, to_copy| {
+                // SAFETY: The sum of `offset` and `to_copy` is bounded by the size of T.
+                let obj_ptr = (obj as *const T as *const u8).add(obj_offset);
+                // SAFETY: We have a reference to the object, so the pointer is valid.
+                page.write_raw(obj_ptr, offset, to_copy)?;
+                obj_offset += to_copy;
+                Ok(())
+            })
+        }
+    }
+
+    /// Write zeroes to the given range.
+    ///
+    /// # Safety
+    ///
+    /// All pages touched by this operation must be in use for the duration of this call.
+    pub(crate) unsafe fn fill_zero(&self, offset: usize, size: usize) -> Result {
+        // SAFETY: `self.iterate` has the same safety requirements as `copy_into`.
+        unsafe {
+            self.iterate(offset, size, |page, offset, len| {
+                page.fill_zero_raw(offset, len)
+            })
+        }
+    }
+}
+
+#[pinned_drop]
+impl PinnedDrop for ShrinkablePageRange {
+    fn drop(self: Pin<&mut Self>) {
+        let (pages, size) = {
+            let lock = self.lock.lock();
+            (lock.pages, lock.size)
+        };
+
+        if size == 0 {
+            return;
+        }
+
+        // Note: This call is also necessary for the safety of `stable_trylock_mm`.
+        let mm_lock = self.mm_lock.lock();
+
+        // This is the destructor, so unlike the other methods, we only need to worry about races
+        // with the shrinker here. Since we hold the `mm_lock`, we also can't race with the
+        // shrinker, and after this loop, the shrinker will not access any of our pages since we
+        // removed them from the lru list.
+        for i in 0..size {
+            // SAFETY: Loop is in-bounds of the size.
+            let p_ptr = unsafe { pages.add(i) };
+            // SAFETY: No other readers, so we can read.
+            if let Some(p) = unsafe { PageInfo::get_page(p_ptr) } {
+                // SAFETY: The pointer is valid and it's the right shrinker.
+                unsafe { PageInfo::list_lru_del(p_ptr, p.nid(), self.shrinker) };
+            }
+        }
+
+        drop(mm_lock);
+
+        // SAFETY: `pages` was allocated as an `KVVec<PageInfo>` with capacity `size`. Furthermore,
+        // all `size` elements are initialized. Also, the array is no longer shared with the
+        // shrinker due to the above loop.
+        drop(unsafe { KVVec::from_raw_parts(pages, size, size) });
+    }
+}
+
+/// # Safety
+/// Called by the shrinker.
+#[no_mangle]
+unsafe extern "C" fn rust_shrink_count(
+    shrink: *mut bindings::shrinker,
+    _sc: *mut bindings::shrink_control,
+) -> c_ulong {
+    // SAFETY: We can access our own private data.
+    let list_lru = unsafe { (*shrink).private_data.cast::<bindings::list_lru>() };
+    // SAFETY: Accessing the lru list is okay. Just an FFI call.
+    unsafe { bindings::list_lru_count(list_lru) }
+}
+
+/// # Safety
+/// Called by the shrinker.
+#[no_mangle]
+unsafe extern "C" fn rust_shrink_scan(
+    shrink: *mut bindings::shrinker,
+    sc: *mut bindings::shrink_control,
+) -> c_ulong {
+    // SAFETY: We can access our own private data.
+    let list_lru = unsafe { (*shrink).private_data.cast::<bindings::list_lru>() };
+    // SAFETY: Caller guarantees that it is safe to read this field.
+    let nr_to_scan = unsafe { (*sc).nr_to_scan };
+    // SAFETY: Accessing the lru list is okay. Just an FFI call.
+    unsafe {
+        bindings::list_lru_walk(
+            list_lru,
+            Some(bindings::rust_shrink_free_page_wrap),
+            ptr::null_mut(),
+            nr_to_scan,
+        )
+    }
+}
+
+const LRU_SKIP: bindings::lru_status = bindings::lru_status_LRU_SKIP;
+const LRU_REMOVED_ENTRY: bindings::lru_status = bindings::lru_status_LRU_REMOVED_RETRY;
+
+/// # Safety
+/// Called by the shrinker.
+#[no_mangle]
+unsafe extern "C" fn rust_shrink_free_page(
+    item: *mut bindings::list_head,
+    lru: *mut bindings::list_lru_one,
+    _cb_arg: *mut c_void,
+) -> bindings::lru_status {
+    // Fields that should survive after unlocking the lru lock.
+    let page;
+    let page_index;
+    let mm;
+    let mmap_read;
+    let mm_mutex;
+    let vma_addr;
+
+    {
+        // CAST: The `list_head` field is first in `PageInfo`.
+        let info = item as *mut PageInfo;
+        // SAFETY: The `range` field of `PageInfo` is immutable.
+        let range = unsafe { &*((*info).range) };
+
+        mm = match range.mm.mmget_not_zero() {
+            Some(mm) => MmWithUser::into_mmput_async(mm),
+            None => return LRU_SKIP,
+        };
+
+        mm_mutex = match range.stable_trylock_mm() {
+            Some(guard) => guard,
+            None => return LRU_SKIP,
+        };
+
+        mmap_read = match mm.mmap_read_trylock() {
+            Some(guard) => guard,
+            None => return LRU_SKIP,
+        };
+
+        // We can't lock it normally here, since we hold the lru lock.
+        let inner = match range.lock.try_lock() {
+            Some(inner) => inner,
+            None => return LRU_SKIP,
+        };
+
+        // SAFETY: The item is in this lru list, so it's okay to remove it.
+        unsafe { bindings::list_lru_isolate(lru, item) };
+
+        // SAFETY: Both pointers are in bounds of the same allocation.
+        page_index = unsafe { info.offset_from(inner.pages) } as usize;
+
+        // SAFETY: We hold the spinlock, so we can take the page.
+        //
+        // This sets the page pointer to zero before we unmap it from the vma. However, we call
+        // `zap_page_range` before we release the mmap lock, so `use_page_slow` will not be able to
+        // insert a new page until after our call to `zap_page_range`.
+        page = unsafe { PageInfo::take_page(info) };
+        vma_addr = inner.vma_addr;
+
+        // From this point on, we don't access this PageInfo or ShrinkablePageRange again, because
+        // they can be freed at any point after we unlock `lru_lock`. This is with the exception of
+        // `mm_mutex` which is kept alive by holding the lock.
+    }
+
+    // SAFETY: The lru lock is locked when this method is called.
+    unsafe { bindings::spin_unlock(&raw mut (*lru).lock) };
+
+    if let Some(vma) = mmap_read.vma_lookup(vma_addr) {
+        let user_page_addr = vma_addr + (page_index << PAGE_SHIFT);
+        vma.zap_page_range_single(user_page_addr, PAGE_SIZE);
+    }
+
+    drop(mmap_read);
+    drop(mm_mutex);
+    drop(mm);
+    drop(page);
+
+    // SAFETY: We just unlocked the lru lock, but it should be locked when we return.
+    unsafe { bindings::spin_lock(&raw mut (*lru).lock) };
+
+    LRU_REMOVED_ENTRY
+}

drivers/android/binder/page_range_helper.c

@@ -0,0 +1,24 @@
+// SPDX-License-Identifier: GPL-2.0
+
+/* C helper for page_range.rs to work around a CFI violation.
+ *
+ * Bindgen currently pretends that `enum lru_status` is the same as an integer.
+ * This assumption is fine ABI-wise, but once you add CFI to the mix, it
+ * triggers a CFI violation because `enum lru_status` gets a different CFI tag.
+ *
+ * This file contains a workaround until bindgen can be fixed.
+ *
+ * Copyright (C) 2025 Google LLC.
+ */
+#include "page_range_helper.h"
+
+unsigned int rust_shrink_free_page(struct list_head *item,
+				   struct list_lru_one *list,
+				   void *cb_arg);
+
+enum lru_status
+rust_shrink_free_page_wrap(struct list_head *item, struct list_lru_one *list,
+			   void *cb_arg)
+{
+	return rust_shrink_free_page(item, list, cb_arg);
+}

drivers/android/binder/page_range_helper.h

@@ -0,0 +1,15 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Copyright (C) 2025 Google, Inc.
+ */
+
+#ifndef _LINUX_PAGE_RANGE_HELPER_H
+#define _LINUX_PAGE_RANGE_HELPER_H
+
+#include <linux/list_lru.h>
+
+enum lru_status
+rust_shrink_free_page_wrap(struct list_head *item, struct list_lru_one *list,
+			   void *cb_arg);
+
+#endif /* _LINUX_PAGE_RANGE_HELPER_H */

drivers/android/binder/range_alloc/array.rs

@@ -0,0 +1,251 @@
+// SPDX-License-Identifier: GPL-2.0
+
+// Copyright (C) 2025 Google LLC.
+
+use kernel::{
+    page::{PAGE_MASK, PAGE_SIZE},
+    prelude::*,
+    seq_file::SeqFile,
+    seq_print,
+    task::Pid,
+};
+
+use crate::range_alloc::{DescriptorState, FreedRange, Range};
+
+/// Keeps track of allocations in a process' mmap.
+///
+/// Each process has an mmap where the data for incoming transactions will be placed. This struct
+/// keeps track of allocations made in the mmap. For each allocation, we store a descriptor that
+/// has metadata related to the allocation. We also keep track of available free space.
+pub(super) struct ArrayRangeAllocator<T> {
+    /// This stores all ranges that are allocated. Unlike the tree based allocator, we do *not*
+    /// store the free ranges.
+    ///
+    /// Sorted by offset.
+    pub(super) ranges: KVec<Range<T>>,
+    size: usize,
+    free_oneway_space: usize,
+}
+
+struct FindEmptyRes {
+    /// Which index in `ranges` should we insert the new range at?
+    ///
+    /// Inserting the new range at this index keeps `ranges` sorted.
+    insert_at_idx: usize,
+    /// Which offset should we insert the new range at?
+    insert_at_offset: usize,
+}
+
+impl<T> ArrayRangeAllocator<T> {
+    pub(crate) fn new(size: usize, alloc: EmptyArrayAlloc<T>) -> Self {
+        Self {
+            ranges: alloc.ranges,
+            size,
+            free_oneway_space: size / 2,
+        }
+    }
+
+    pub(crate) fn free_oneway_space(&self) -> usize {
+        self.free_oneway_space
+    }
+
+    pub(crate) fn count_buffers(&self) -> usize {
+        self.ranges.len()
+    }
+
+    pub(crate) fn total_size(&self) -> usize {
+        self.size
+    }
+
+    pub(crate) fn is_full(&self) -> bool {
+        self.ranges.len() == self.ranges.capacity()
+    }
+
+    pub(crate) fn debug_print(&self, m: &SeqFile) -> Result<()> {
+        for range in &self.ranges {
+            seq_print!(
+                m,
+                "  buffer {}: {} size {} pid {} oneway {}",
+                0,
+                range.offset,
+                range.size,
+                range.state.pid(),
+                range.state.is_oneway(),
+            );
+            if let DescriptorState::Reserved(_) = range.state {
+                seq_print!(m, " reserved\n");
+            } else {
+                seq_print!(m, " allocated\n");
+            }
+        }
+        Ok(())
+    }
+
+    /// Find somewhere to put a new range.
+    ///
+    /// Unlike the tree implementation, we do not bother to find the smallest gap. The idea is that
+    /// fragmentation isn't a big issue when we don't have many ranges.
+    ///
+    /// Returns the index that the new range should have in `self.ranges` after insertion.
+    fn find_empty_range(&self, size: usize) -> Option<FindEmptyRes> {
+        let after_last_range = self.ranges.last().map(Range::endpoint).unwrap_or(0);
+
+        if size <= self.total_size() - after_last_range {
+            // We can put the range at the end, so just do that.
+            Some(FindEmptyRes {
+                insert_at_idx: self.ranges.len(),
+                insert_at_offset: after_last_range,
+            })
+        } else {
+            let mut end_of_prev = 0;
+            for (i, range) in self.ranges.iter().enumerate() {
+                // Does it fit before the i'th range?
+                if size <= range.offset - end_of_prev {
+                    return Some(FindEmptyRes {
+                        insert_at_idx: i,
+                        insert_at_offset: end_of_prev,
+                    });
+                }
+                end_of_prev = range.endpoint();
+            }
+            None
+        }
+    }
+
+    pub(crate) fn reserve_new(
+        &mut self,
+        debug_id: usize,
+        size: usize,
+        is_oneway: bool,
+        pid: Pid,
+    ) -> Result<usize> {
+        // Compute new value of free_oneway_space, which is set only on success.
+        let new_oneway_space = if is_oneway {
+            match self.free_oneway_space.checked_sub(size) {
+                Some(new_oneway_space) => new_oneway_space,
+                None => return Err(ENOSPC),
+            }
+        } else {
+            self.free_oneway_space
+        };
+
+        let FindEmptyRes {
+            insert_at_idx,
+            insert_at_offset,
+        } = self.find_empty_range(size).ok_or(ENOSPC)?;
+        self.free_oneway_space = new_oneway_space;
+
+        let new_range = Range {
+            offset: insert_at_offset,
+            size,
+            state: DescriptorState::new(is_oneway, debug_id, pid),
+        };
+        // Insert the value at the given index to keep the array sorted.
+        self.ranges
+            .insert_within_capacity(insert_at_idx, new_range)
+            .ok()
+            .unwrap();
+
+        Ok(insert_at_offset)
+    }
+
+    pub(crate) fn reservation_abort(&mut self, offset: usize) -> Result<FreedRange> {
+        // This could use a binary search, but linear scans are usually faster for small arrays.
+        let i = self
+            .ranges
+            .iter()
+            .position(|range| range.offset == offset)
+            .ok_or(EINVAL)?;
+        let range = &self.ranges[i];
+
+        if let DescriptorState::Allocated(_) = range.state {
+            return Err(EPERM);
+        }
+
+        let size = range.size;
+        let offset = range.offset;
+
+        if range.state.is_oneway() {
+            self.free_oneway_space += size;
+        }
+
+        // This computes the range of pages that are no longer used by *any* allocated range. The
+        // caller will mark them as unused, which means that they can be freed if the system comes
+        // under memory pressure.
+        let mut freed_range = FreedRange::interior_pages(offset, size);
+        #[expect(clippy::collapsible_if)] // reads better like this
+        if offset % PAGE_SIZE != 0 {
+            if i == 0 || self.ranges[i - 1].endpoint() <= (offset & PAGE_MASK) {
+                freed_range.start_page_idx -= 1;
+            }
+        }
+        if range.endpoint() % PAGE_SIZE != 0 {
+            let page_after = (range.endpoint() & PAGE_MASK) + PAGE_SIZE;
+            if i + 1 == self.ranges.len() || page_after <= self.ranges[i + 1].offset {
+                freed_range.end_page_idx += 1;
+            }
+        }
+
+        self.ranges.remove(i)?;
+        Ok(freed_range)
+    }
+
+    pub(crate) fn reservation_commit(&mut self, offset: usize, data: &mut Option<T>) -> Result {
+        // This could use a binary search, but linear scans are usually faster for small arrays.
+        let range = self
+            .ranges
+            .iter_mut()
+            .find(|range| range.offset == offset)
+            .ok_or(ENOENT)?;
+
+        let DescriptorState::Reserved(reservation) = &range.state else {
+            return Err(ENOENT);
+        };
+
+        range.state = DescriptorState::Allocated(reservation.clone().allocate(data.take()));
+        Ok(())
+    }
+
+    pub(crate) fn reserve_existing(&mut self, offset: usize) -> Result<(usize, usize, Option<T>)> {
+        // This could use a binary search, but linear scans are usually faster for small arrays.
+        let range = self
+            .ranges
+            .iter_mut()
+            .find(|range| range.offset == offset)
+            .ok_or(ENOENT)?;
+
+        let DescriptorState::Allocated(allocation) = &mut range.state else {
+            return Err(ENOENT);
+        };
+
+        let data = allocation.take();
+        let debug_id = allocation.reservation.debug_id;
+        range.state = DescriptorState::Reserved(allocation.reservation.clone());
+        Ok((range.size, debug_id, data))
+    }
+
+    pub(crate) fn take_for_each<F: Fn(usize, usize, usize, Option<T>)>(&mut self, callback: F) {
+        for range in self.ranges.iter_mut() {
+            if let DescriptorState::Allocated(allocation) = &mut range.state {
+                callback(
+                    range.offset,
+                    range.size,
+                    allocation.reservation.debug_id,
+                    allocation.data.take(),
+                );
+            }
+        }
+    }
+}
+
+pub(crate) struct EmptyArrayAlloc<T> {
+    ranges: KVec<Range<T>>,
+}
+
+impl<T> EmptyArrayAlloc<T> {
+    pub(crate) fn try_new(capacity: usize) -> Result<Self> {
+        Ok(Self {
+            ranges: KVec::with_capacity(capacity, GFP_KERNEL)?,
+        })
+    }
+}

drivers/android/binder/range_alloc/mod.rs

@@ -0,0 +1,329 @@
+// SPDX-License-Identifier: GPL-2.0
+
+// Copyright (C) 2025 Google LLC.
+
+use kernel::{page::PAGE_SIZE, prelude::*, seq_file::SeqFile, task::Pid};
+
+mod tree;
+use self::tree::{FromArrayAllocs, ReserveNewTreeAlloc, TreeRangeAllocator};
+
+mod array;
+use self::array::{ArrayRangeAllocator, EmptyArrayAlloc};
+
+enum DescriptorState<T> {
+    Reserved(Reservation),
+    Allocated(Allocation<T>),
+}
+
+impl<T> DescriptorState<T> {
+    fn new(is_oneway: bool, debug_id: usize, pid: Pid) -> Self {
+        DescriptorState::Reserved(Reservation {
+            debug_id,
+            is_oneway,
+            pid,
+        })
+    }
+
+    fn pid(&self) -> Pid {
+        match self {
+            DescriptorState::Reserved(inner) => inner.pid,
+            DescriptorState::Allocated(inner) => inner.reservation.pid,
+        }
+    }
+
+    fn is_oneway(&self) -> bool {
+        match self {
+            DescriptorState::Reserved(inner) => inner.is_oneway,
+            DescriptorState::Allocated(inner) => inner.reservation.is_oneway,
+        }
+    }
+}
+
+#[derive(Clone)]
+struct Reservation {
+    debug_id: usize,
+    is_oneway: bool,
+    pid: Pid,
+}
+
+impl Reservation {
+    fn allocate<T>(self, data: Option<T>) -> Allocation<T> {
+        Allocation {
+            data,
+            reservation: self,
+        }
+    }
+}
+
+struct Allocation<T> {
+    reservation: Reservation,
+    data: Option<T>,
+}
+
+impl<T> Allocation<T> {
+    fn deallocate(self) -> (Reservation, Option<T>) {
+        (self.reservation, self.data)
+    }
+
+    fn debug_id(&self) -> usize {
+        self.reservation.debug_id
+    }
+
+    fn take(&mut self) -> Option<T> {
+        self.data.take()
+    }
+}
+
+/// The array implementation must switch to the tree if it wants to go beyond this number of
+/// ranges.
+const TREE_THRESHOLD: usize = 8;
+
+/// Represents a range of pages that have just become completely free.
+#[derive(Copy, Clone)]
+pub(crate) struct FreedRange {
+    pub(crate) start_page_idx: usize,
+    pub(crate) end_page_idx: usize,
+}
+
+impl FreedRange {
+    fn interior_pages(offset: usize, size: usize) -> FreedRange {
+        FreedRange {
+            // Divide round up
+            start_page_idx: offset.div_ceil(PAGE_SIZE),
+            // Divide round down
+            end_page_idx: (offset + size) / PAGE_SIZE,
+        }
+    }
+}
+
+struct Range<T> {
+    offset: usize,
+    size: usize,
+    state: DescriptorState<T>,
+}
+
+impl<T> Range<T> {
+    fn endpoint(&self) -> usize {
+        self.offset + self.size
+    }
+}
+
+pub(crate) struct RangeAllocator<T> {
+    inner: Impl<T>,
+}
+
+enum Impl<T> {
+    Empty(usize),
+    Array(ArrayRangeAllocator<T>),
+    Tree(TreeRangeAllocator<T>),
+}
+
+impl<T> RangeAllocator<T> {
+    pub(crate) fn new(size: usize) -> Self {
+        Self {
+            inner: Impl::Empty(size),
+        }
+    }
+
+    pub(crate) fn free_oneway_space(&self) -> usize {
+        match &self.inner {
+            Impl::Empty(size) => size / 2,
+            Impl::Array(array) => array.free_oneway_space(),
+            Impl::Tree(tree) => tree.free_oneway_space(),
+        }
+    }
+
+    pub(crate) fn count_buffers(&self) -> usize {
+        match &self.inner {
+            Impl::Empty(_size) => 0,
+            Impl::Array(array) => array.count_buffers(),
+            Impl::Tree(tree) => tree.count_buffers(),
+        }
+    }
+
+    pub(crate) fn debug_print(&self, m: &SeqFile) -> Result<()> {
+        match &self.inner {
+            Impl::Empty(_size) => Ok(()),
+            Impl::Array(array) => array.debug_print(m),
+            Impl::Tree(tree) => tree.debug_print(m),
+        }
+    }
+
+    /// Try to reserve a new buffer, using the provided allocation if necessary.
+    pub(crate) fn reserve_new(&mut self, mut args: ReserveNewArgs<T>) -> Result<ReserveNew<T>> {
+        match &mut self.inner {
+            Impl::Empty(size) => {
+                let empty_array = match args.empty_array_alloc.take() {
+                    Some(empty_array) => ArrayRangeAllocator::new(*size, empty_array),
+                    None => {
+                        return Ok(ReserveNew::NeedAlloc(ReserveNewNeedAlloc {
+                            args,
+                            need_empty_array_alloc: true,
+                            need_new_tree_alloc: false,
+                            need_tree_alloc: false,
+                        }))
+                    }
+                };
+
+                self.inner = Impl::Array(empty_array);
+                self.reserve_new(args)
+            }
+            Impl::Array(array) if array.is_full() => {
+                let allocs = match args.new_tree_alloc {
+                    Some(ref mut allocs) => allocs,
+                    None => {
+                        return Ok(ReserveNew::NeedAlloc(ReserveNewNeedAlloc {
+                            args,
+                            need_empty_array_alloc: false,
+                            need_new_tree_alloc: true,
+                            need_tree_alloc: true,
+                        }))
+                    }
+                };
+
+                let new_tree =
+                    TreeRangeAllocator::from_array(array.total_size(), &mut array.ranges, allocs);
+
+                self.inner = Impl::Tree(new_tree);
+                self.reserve_new(args)
+            }
+            Impl::Array(array) => {
+                let offset =
+                    array.reserve_new(args.debug_id, args.size, args.is_oneway, args.pid)?;
+                Ok(ReserveNew::Success(ReserveNewSuccess {
+                    offset,
+                    oneway_spam_detected: false,
+                    _empty_array_alloc: args.empty_array_alloc,
+                    _new_tree_alloc: args.new_tree_alloc,
+                    _tree_alloc: args.tree_alloc,
+                }))
+            }
+            Impl::Tree(tree) => {
+                let alloc = match args.tree_alloc {
+                    Some(alloc) => alloc,
+                    None => {
+                        return Ok(ReserveNew::NeedAlloc(ReserveNewNeedAlloc {
+                            args,
+                            need_empty_array_alloc: false,
+                            need_new_tree_alloc: false,
+                            need_tree_alloc: true,
+                        }));
+                    }
+                };
+                let (offset, oneway_spam_detected) =
+                    tree.reserve_new(args.debug_id, args.size, args.is_oneway, args.pid, alloc)?;
+                Ok(ReserveNew::Success(ReserveNewSuccess {
+                    offset,
+                    oneway_spam_detected,
+                    _empty_array_alloc: args.empty_array_alloc,
+                    _new_tree_alloc: args.new_tree_alloc,
+                    _tree_alloc: None,
+                }))
+            }
+        }
+    }
+
+    /// Deletes the allocations at `offset`.
+    pub(crate) fn reservation_abort(&mut self, offset: usize) -> Result<FreedRange> {
+        match &mut self.inner {
+            Impl::Empty(_size) => Err(EINVAL),
+            Impl::Array(array) => array.reservation_abort(offset),
+            Impl::Tree(tree) => {
+                let freed_range = tree.reservation_abort(offset)?;
+                if tree.is_empty() {
+                    self.inner = Impl::Empty(tree.total_size());
+                }
+                Ok(freed_range)
+            }
+        }
+    }
+
+    /// Called when an allocation is no longer in use by the kernel.
+    ///
+    /// The value in `data` will be stored, if any. A mutable reference is used to avoid dropping
+    /// the `T` when an error is returned.
+    pub(crate) fn reservation_commit(&mut self, offset: usize, data: &mut Option<T>) -> Result {
+        match &mut self.inner {
+            Impl::Empty(_size) => Err(EINVAL),
+            Impl::Array(array) => array.reservation_commit(offset, data),
+            Impl::Tree(tree) => tree.reservation_commit(offset, data),
+        }
+    }
+
+    /// Called when the kernel starts using an allocation.
+    ///
+    /// Returns the size of the existing entry and the data associated with it.
+    pub(crate) fn reserve_existing(&mut self, offset: usize) -> Result<(usize, usize, Option<T>)> {
+        match &mut self.inner {
+            Impl::Empty(_size) => Err(EINVAL),
+            Impl::Array(array) => array.reserve_existing(offset),
+            Impl::Tree(tree) => tree.reserve_existing(offset),
+        }
+    }
+
+    /// Call the provided callback at every allocated region.
+    ///
+    /// This destroys the range allocator. Used only during shutdown.
+    pub(crate) fn take_for_each<F: Fn(usize, usize, usize, Option<T>)>(&mut self, callback: F) {
+        match &mut self.inner {
+            Impl::Empty(_size) => {}
+            Impl::Array(array) => array.take_for_each(callback),
+            Impl::Tree(tree) => tree.take_for_each(callback),
+        }
+    }
+}
+
+/// The arguments for `reserve_new`.
+#[derive(Default)]
+pub(crate) struct ReserveNewArgs<T> {
+    pub(crate) size: usize,
+    pub(crate) is_oneway: bool,
+    pub(crate) debug_id: usize,
+    pub(crate) pid: Pid,
+    pub(crate) empty_array_alloc: Option<EmptyArrayAlloc<T>>,
+    pub(crate) new_tree_alloc: Option<FromArrayAllocs<T>>,
+    pub(crate) tree_alloc: Option<ReserveNewTreeAlloc<T>>,
+}
+
+/// The return type of `ReserveNew`.
+pub(crate) enum ReserveNew<T> {
+    Success(ReserveNewSuccess<T>),
+    NeedAlloc(ReserveNewNeedAlloc<T>),
+}
+
+/// Returned by `reserve_new` when the reservation was successul.
+pub(crate) struct ReserveNewSuccess<T> {
+    pub(crate) offset: usize,
+    pub(crate) oneway_spam_detected: bool,
+
+    // If the user supplied an allocation that we did not end up using, then we return it here.
+    // The caller will kfree it outside of the lock.
+    _empty_array_alloc: Option<EmptyArrayAlloc<T>>,
+    _new_tree_alloc: Option<FromArrayAllocs<T>>,
+    _tree_alloc: Option<ReserveNewTreeAlloc<T>>,
+}
+
+/// Returned by `reserve_new` to request the caller to make an allocation before calling the method
+/// again.
+pub(crate) struct ReserveNewNeedAlloc<T> {
+    args: ReserveNewArgs<T>,
+    need_empty_array_alloc: bool,
+    need_new_tree_alloc: bool,
+    need_tree_alloc: bool,
+}
+
+impl<T> ReserveNewNeedAlloc<T> {
+    /// Make the necessary allocations for another call to `reserve_new`.
+    pub(crate) fn make_alloc(mut self) -> Result<ReserveNewArgs<T>> {
+        if self.need_empty_array_alloc && self.args.empty_array_alloc.is_none() {
+            self.args.empty_array_alloc = Some(EmptyArrayAlloc::try_new(TREE_THRESHOLD)?);
+        }
+        if self.need_new_tree_alloc && self.args.new_tree_alloc.is_none() {
+            self.args.new_tree_alloc = Some(FromArrayAllocs::try_new(TREE_THRESHOLD)?);
+        }
+        if self.need_tree_alloc && self.args.tree_alloc.is_none() {
+            self.args.tree_alloc = Some(ReserveNewTreeAlloc::try_new()?);
+        }
+        Ok(self.args)
+    }
+}

drivers/android/binder/range_alloc/tree.rs

@@ -0,0 +1,488 @@
+// SPDX-License-Identifier: GPL-2.0
+
+// Copyright (C) 2025 Google LLC.
+
+use kernel::{
+    page::PAGE_SIZE,
+    prelude::*,
+    rbtree::{RBTree, RBTreeNode, RBTreeNodeReservation},
+    seq_file::SeqFile,
+    seq_print,
+    task::Pid,
+};
+
+use crate::range_alloc::{DescriptorState, FreedRange, Range};
+
+/// Keeps track of allocations in a process' mmap.
+///
+/// Each process has an mmap where the data for incoming transactions will be placed. This struct
+/// keeps track of allocations made in the mmap. For each allocation, we store a descriptor that
+/// has metadata related to the allocation. We also keep track of available free space.
+pub(super) struct TreeRangeAllocator<T> {
+    /// This collection contains descriptors for *both* ranges containing an allocation, *and* free
+    /// ranges between allocations. The free ranges get merged, so there are never two free ranges
+    /// next to each other.
+    tree: RBTree<usize, Descriptor<T>>,
+    /// Contains an entry for every free range in `self.tree`. This tree sorts the ranges by size,
+    /// letting us look up the smallest range whose size is at least some lower bound.
+    free_tree: RBTree<FreeKey, ()>,
+    size: usize,
+    free_oneway_space: usize,
+}
+
+impl<T> TreeRangeAllocator<T> {
+    pub(crate) fn from_array(
+        size: usize,
+        ranges: &mut KVec<Range<T>>,
+        alloc: &mut FromArrayAllocs<T>,
+    ) -> Self {
+        let mut tree = TreeRangeAllocator {
+            tree: RBTree::new(),
+            free_tree: RBTree::new(),
+            size,
+            free_oneway_space: size / 2,
+        };
+
+        let mut free_offset = 0;
+        for range in ranges.drain_all() {
+            let free_size = range.offset - free_offset;
+            if free_size > 0 {
+                let free_node = alloc.free_tree.pop().unwrap();
+                tree.free_tree
+                    .insert(free_node.into_node((free_size, free_offset), ()));
+                let tree_node = alloc.tree.pop().unwrap();
+                tree.tree.insert(
+                    tree_node.into_node(free_offset, Descriptor::new(free_offset, free_size)),
+                );
+            }
+            free_offset = range.endpoint();
+
+            if range.state.is_oneway() {
+                tree.free_oneway_space = tree.free_oneway_space.saturating_sub(range.size);
+            }
+
+            let free_res = alloc.free_tree.pop().unwrap();
+            let tree_node = alloc.tree.pop().unwrap();
+            let mut desc = Descriptor::new(range.offset, range.size);
+            desc.state = Some((range.state, free_res));
+            tree.tree.insert(tree_node.into_node(range.offset, desc));
+        }
+
+        // After the last range, we may need a free range.
+        if free_offset < size {
+            let free_size = size - free_offset;
+            let free_node = alloc.free_tree.pop().unwrap();
+            tree.free_tree
+                .insert(free_node.into_node((free_size, free_offset), ()));
+            let tree_node = alloc.tree.pop().unwrap();
+            tree.tree
+                .insert(tree_node.into_node(free_offset, Descriptor::new(free_offset, free_size)));
+        }
+
+        tree
+    }
+
+    pub(crate) fn is_empty(&self) -> bool {
+        let mut tree_iter = self.tree.values();
+        // There's always at least one range, because index zero is either the start of a free or
+        // allocated range.
+        let first_value = tree_iter.next().unwrap();
+        if tree_iter.next().is_some() {
+            // There are never two free ranges next to each other, so if there is more than one
+            // descriptor, then at least one of them must hold an allocated range.
+            return false;
+        }
+        // There is only one descriptor. Return true if it is for a free range.
+        first_value.state.is_none()
+    }
+
+    pub(crate) fn total_size(&self) -> usize {
+        self.size
+    }
+
+    pub(crate) fn free_oneway_space(&self) -> usize {
+        self.free_oneway_space
+    }
+
+    pub(crate) fn count_buffers(&self) -> usize {
+        self.tree
+            .values()
+            .filter(|desc| desc.state.is_some())
+            .count()
+    }
+
+    pub(crate) fn debug_print(&self, m: &SeqFile) -> Result<()> {
+        for desc in self.tree.values() {
+            let state = match &desc.state {
+                Some(state) => &state.0,
+                None => continue,
+            };
+            seq_print!(
+                m,
+                "  buffer: {} size {} pid {}",
+                desc.offset,
+                desc.size,
+                state.pid(),
+            );
+            if state.is_oneway() {
+                seq_print!(m, " oneway");
+            }
+            match state {
+                DescriptorState::Reserved(_res) => {
+                    seq_print!(m, " reserved\n");
+                }
+                DescriptorState::Allocated(_alloc) => {
+                    seq_print!(m, " allocated\n");
+                }
+            }
+        }
+        Ok(())
+    }
+
+    fn find_best_match(&mut self, size: usize) -> Option<&mut Descriptor<T>> {
+        let free_cursor = self.free_tree.cursor_lower_bound(&(size, 0))?;
+        let ((_, offset), ()) = free_cursor.current();
+        self.tree.get_mut(offset)
+    }
+
+    /// Try to reserve a new buffer, using the provided allocation if necessary.
+    pub(crate) fn reserve_new(
+        &mut self,
+        debug_id: usize,
+        size: usize,
+        is_oneway: bool,
+        pid: Pid,
+        alloc: ReserveNewTreeAlloc<T>,
+    ) -> Result<(usize, bool)> {
+        // Compute new value of free_oneway_space, which is set only on success.
+        let new_oneway_space = if is_oneway {
+            match self.free_oneway_space.checked_sub(size) {
+                Some(new_oneway_space) => new_oneway_space,
+                None => return Err(ENOSPC),
+            }
+        } else {
+            self.free_oneway_space
+        };
+
+        // Start detecting spammers once we have less than 20%
+        // of async space left (which is less than 10% of total
+        // buffer size).
+        //
+        // (This will short-circut, so `low_oneway_space` is
+        // only called when necessary.)
+        let oneway_spam_detected =
+            is_oneway && new_oneway_space < self.size / 10 && self.low_oneway_space(pid);
+
+        let (found_size, found_off, tree_node, free_tree_node) = match self.find_best_match(size) {
+            None => {
+                pr_warn!("ENOSPC from range_alloc.reserve_new - size: {}", size);
+                return Err(ENOSPC);
+            }
+            Some(desc) => {
+                let found_size = desc.size;
+                let found_offset = desc.offset;
+
+                // In case we need to break up the descriptor
+                let new_desc = Descriptor::new(found_offset + size, found_size - size);
+                let (tree_node, free_tree_node, desc_node_res) = alloc.initialize(new_desc);
+
+                desc.state = Some((
+                    DescriptorState::new(is_oneway, debug_id, pid),
+                    desc_node_res,
+                ));
+                desc.size = size;
+
+                (found_size, found_offset, tree_node, free_tree_node)
+            }
+        };
+        self.free_oneway_space = new_oneway_space;
+        self.free_tree.remove(&(found_size, found_off));
+
+        if found_size != size {
+            self.tree.insert(tree_node);
+            self.free_tree.insert(free_tree_node);
+        }
+
+        Ok((found_off, oneway_spam_detected))
+    }
+
+    pub(crate) fn reservation_abort(&mut self, offset: usize) -> Result<FreedRange> {
+        let mut cursor = self.tree.cursor_lower_bound(&offset).ok_or_else(|| {
+            pr_warn!(
+                "EINVAL from range_alloc.reservation_abort - offset: {}",
+                offset
+            );
+            EINVAL
+        })?;
+
+        let (_, desc) = cursor.current_mut();
+
+        if desc.offset != offset {
+            pr_warn!(
+                "EINVAL from range_alloc.reservation_abort - offset: {}",
+                offset
+            );
+            return Err(EINVAL);
+        }
+
+        let (reservation, free_node_res) = desc.try_change_state(|state| match state {
+            Some((DescriptorState::Reserved(reservation), free_node_res)) => {
+                (None, Ok((reservation, free_node_res)))
+            }
+            None => {
+                pr_warn!(
+                    "EINVAL from range_alloc.reservation_abort - offset: {}",
+                    offset
+                );
+                (None, Err(EINVAL))
+            }
+            allocated => {
+                pr_warn!(
+                    "EPERM from range_alloc.reservation_abort - offset: {}",
+                    offset
+                );
+                (allocated, Err(EPERM))
+            }
+        })?;
+
+        let mut size = desc.size;
+        let mut offset = desc.offset;
+        let free_oneway_space_add = if reservation.is_oneway { size } else { 0 };
+
+        self.free_oneway_space += free_oneway_space_add;
+
+        let mut freed_range = FreedRange::interior_pages(offset, size);
+        // Compute how large the next free region needs to be to include one more page in
+        // the newly freed range.
+        let add_next_page_needed = match (offset + size) % PAGE_SIZE {
+            0 => usize::MAX,
+            unalign => PAGE_SIZE - unalign,
+        };
+        // Compute how large the previous free region needs to be to include one more page
+        // in the newly freed range.
+        let add_prev_page_needed = match offset % PAGE_SIZE {
+            0 => usize::MAX,
+            unalign => unalign,
+        };
+
+        // Merge next into current if next is free
+        let remove_next = match cursor.peek_next() {
+            Some((_, next)) if next.state.is_none() => {
+                if next.size >= add_next_page_needed {
+                    freed_range.end_page_idx += 1;
+                }
+                self.free_tree.remove(&(next.size, next.offset));
+                size += next.size;
+                true
+            }
+            _ => false,
+        };
+
+        if remove_next {
+            let (_, desc) = cursor.current_mut();
+            desc.size = size;
+            cursor.remove_next();
+        }
+
+        // Merge current into prev if prev is free
+        match cursor.peek_prev_mut() {
+            Some((_, prev)) if prev.state.is_none() => {
+                if prev.size >= add_prev_page_needed {
+                    freed_range.start_page_idx -= 1;
+                }
+                // merge previous with current, remove current
+                self.free_tree.remove(&(prev.size, prev.offset));
+                offset = prev.offset;
+                size += prev.size;
+                prev.size = size;
+                cursor.remove_current();
+            }
+            _ => {}
+        };
+
+        self.free_tree
+            .insert(free_node_res.into_node((size, offset), ()));
+
+        Ok(freed_range)
+    }
+
+    pub(crate) fn reservation_commit(&mut self, offset: usize, data: &mut Option<T>) -> Result {
+        let desc = self.tree.get_mut(&offset).ok_or(ENOENT)?;
+
+        desc.try_change_state(|state| match state {
+            Some((DescriptorState::Reserved(reservation), free_node_res)) => (
+                Some((
+                    DescriptorState::Allocated(reservation.allocate(data.take())),
+                    free_node_res,
+                )),
+                Ok(()),
+            ),
+            other => (other, Err(ENOENT)),
+        })
+    }
+
+    /// Takes an entry at the given offset from [`DescriptorState::Allocated`] to
+    /// [`DescriptorState::Reserved`].
+    ///
+    /// Returns the size of the existing entry and the data associated with it.
+    pub(crate) fn reserve_existing(&mut self, offset: usize) -> Result<(usize, usize, Option<T>)> {
+        let desc = self.tree.get_mut(&offset).ok_or_else(|| {
+            pr_warn!(
+                "ENOENT from range_alloc.reserve_existing - offset: {}",
+                offset
+            );
+            ENOENT
+        })?;
+
+        let (debug_id, data) = desc.try_change_state(|state| match state {
+            Some((DescriptorState::Allocated(allocation), free_node_res)) => {
+                let (reservation, data) = allocation.deallocate();
+                let debug_id = reservation.debug_id;
+                (
+                    Some((DescriptorState::Reserved(reservation), free_node_res)),
+                    Ok((debug_id, data)),
+                )
+            }
+            other => {
+                pr_warn!(
+                    "ENOENT from range_alloc.reserve_existing - offset: {}",
+                    offset
+                );
+                (other, Err(ENOENT))
+            }
+        })?;
+
+        Ok((desc.size, debug_id, data))
+    }
+
+    /// Call the provided callback at every allocated region.
+    ///
+    /// This destroys the range allocator. Used only during shutdown.
+    pub(crate) fn take_for_each<F: Fn(usize, usize, usize, Option<T>)>(&mut self, callback: F) {
+        for (_, desc) in self.tree.iter_mut() {
+            if let Some((DescriptorState::Allocated(allocation), _)) = &mut desc.state {
+                callback(
+                    desc.offset,
+                    desc.size,
+                    allocation.debug_id(),
+                    allocation.take(),
+                );
+            }
+        }
+    }
+
+    /// Find the amount and size of buffers allocated by the current caller.
+    ///
+    /// The idea is that once we cross the threshold, whoever is responsible
+    /// for the low async space is likely to try to send another async transaction,
+    /// and at some point we'll catch them in the act.  This is more efficient
+    /// than keeping a map per pid.
+    fn low_oneway_space(&self, calling_pid: Pid) -> bool {
+        let mut total_alloc_size = 0;
+        let mut num_buffers = 0;
+        for (_, desc) in self.tree.iter() {
+            if let Some((state, _)) = &desc.state {
+                if state.is_oneway() && state.pid() == calling_pid {
+                    total_alloc_size += desc.size;
+                    num_buffers += 1;
+                }
+            }
+        }
+
+        // Warn if this pid has more than 50 transactions, or more than 50% of
+        // async space (which is 25% of total buffer size). Oneway spam is only
+        // detected when the threshold is exceeded.
+        num_buffers > 50 || total_alloc_size > self.size / 4
+    }
+}
+
+type TreeDescriptorState<T> = (DescriptorState<T>, FreeNodeRes);
+struct Descriptor<T> {
+    size: usize,
+    offset: usize,
+    state: Option<TreeDescriptorState<T>>,
+}
+
+impl<T> Descriptor<T> {
+    fn new(offset: usize, size: usize) -> Self {
+        Self {
+            size,
+            offset,
+            state: None,
+        }
+    }
+
+    fn try_change_state<F, Data>(&mut self, f: F) -> Result<Data>
+    where
+        F: FnOnce(Option<TreeDescriptorState<T>>) -> (Option<TreeDescriptorState<T>>, Result<Data>),
+    {
+        let (new_state, result) = f(self.state.take());
+        self.state = new_state;
+        result
+    }
+}
+
+// (Descriptor.size, Descriptor.offset)
+type FreeKey = (usize, usize);
+type FreeNodeRes = RBTreeNodeReservation<FreeKey, ()>;
+
+/// An allocation for use by `reserve_new`.
+pub(crate) struct ReserveNewTreeAlloc<T> {
+    tree_node_res: RBTreeNodeReservation<usize, Descriptor<T>>,
+    free_tree_node_res: FreeNodeRes,
+    desc_node_res: FreeNodeRes,
+}
+
+impl<T> ReserveNewTreeAlloc<T> {
+    pub(crate) fn try_new() -> Result<Self> {
+        let tree_node_res = RBTreeNodeReservation::new(GFP_KERNEL)?;
+        let free_tree_node_res = RBTreeNodeReservation::new(GFP_KERNEL)?;
+        let desc_node_res = RBTreeNodeReservation::new(GFP_KERNEL)?;
+        Ok(Self {
+            tree_node_res,
+            free_tree_node_res,
+            desc_node_res,
+        })
+    }
+
+    fn initialize(
+        self,
+        desc: Descriptor<T>,
+    ) -> (
+        RBTreeNode<usize, Descriptor<T>>,
+        RBTreeNode<FreeKey, ()>,
+        FreeNodeRes,
+    ) {
+        let size = desc.size;
+        let offset = desc.offset;
+        (
+            self.tree_node_res.into_node(offset, desc),
+            self.free_tree_node_res.into_node((size, offset), ()),
+            self.desc_node_res,
+        )
+    }
+}
+
+/// An allocation for creating a tree from an `ArrayRangeAllocator`.
+pub(crate) struct FromArrayAllocs<T> {
+    tree: KVec<RBTreeNodeReservation<usize, Descriptor<T>>>,
+    free_tree: KVec<RBTreeNodeReservation<FreeKey, ()>>,
+}
+
+impl<T> FromArrayAllocs<T> {
+    pub(crate) fn try_new(len: usize) -> Result<Self> {
+        let num_descriptors = 2 * len + 1;
+
+        let mut tree = KVec::with_capacity(num_descriptors, GFP_KERNEL)?;
+        for _ in 0..num_descriptors {
+            tree.push(RBTreeNodeReservation::new(GFP_KERNEL)?, GFP_KERNEL)?;
+        }
+
+        let mut free_tree = KVec::with_capacity(num_descriptors, GFP_KERNEL)?;
+        for _ in 0..num_descriptors {
+            free_tree.push(RBTreeNodeReservation::new(GFP_KERNEL)?, GFP_KERNEL)?;
+        }
+
+        Ok(Self { tree, free_tree })
+    }
+}

drivers/android/binder/rust_binder.h

@@ -0,0 +1,23 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Copyright (C) 2025 Google, Inc.
+ */
+
+#ifndef _LINUX_RUST_BINDER_H
+#define _LINUX_RUST_BINDER_H
+
+#include <uapi/linux/android/binder.h>
+#include <uapi/linux/android/binderfs.h>
+
+/*
+ * These symbols are exposed by `rust_binderfs.c` and exist here so that Rust
+ * Binder can call them.
+ */
+int init_rust_binderfs(void);
+
+struct dentry;
+struct inode;
+struct dentry *rust_binderfs_create_proc_file(struct inode *nodp, int pid);
+void rust_binderfs_remove_file(struct dentry *dentry);
+
+#endif

drivers/android/binder/rust_binder_events.c

@@ -0,0 +1,59 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/* rust_binder_events.c
+ *
+ * Rust Binder tracepoints.
+ *
+ * Copyright 2025 Google LLC
+ */
+
+#include "rust_binder.h"
+
+const char * const binder_command_strings[] = {
+	"BC_TRANSACTION",
+	"BC_REPLY",
+	"BC_ACQUIRE_RESULT",
+	"BC_FREE_BUFFER",
+	"BC_INCREFS",
+	"BC_ACQUIRE",
+	"BC_RELEASE",
+	"BC_DECREFS",
+	"BC_INCREFS_DONE",
+	"BC_ACQUIRE_DONE",
+	"BC_ATTEMPT_ACQUIRE",
+	"BC_REGISTER_LOOPER",
+	"BC_ENTER_LOOPER",
+	"BC_EXIT_LOOPER",
+	"BC_REQUEST_DEATH_NOTIFICATION",
+	"BC_CLEAR_DEATH_NOTIFICATION",
+	"BC_DEAD_BINDER_DONE",
+	"BC_TRANSACTION_SG",
+	"BC_REPLY_SG",
+};
+
+const char * const binder_return_strings[] = {
+	"BR_ERROR",
+	"BR_OK",
+	"BR_TRANSACTION",
+	"BR_REPLY",
+	"BR_ACQUIRE_RESULT",
+	"BR_DEAD_REPLY",
+	"BR_TRANSACTION_COMPLETE",
+	"BR_INCREFS",
+	"BR_ACQUIRE",
+	"BR_RELEASE",
+	"BR_DECREFS",
+	"BR_ATTEMPT_ACQUIRE",
+	"BR_NOOP",
+	"BR_SPAWN_LOOPER",
+	"BR_FINISHED",
+	"BR_DEAD_BINDER",
+	"BR_CLEAR_DEATH_NOTIFICATION_DONE",
+	"BR_FAILED_REPLY",
+	"BR_FROZEN_REPLY",
+	"BR_ONEWAY_SPAM_SUSPECT",
+	"BR_TRANSACTION_PENDING_FROZEN"
+};
+
+#define CREATE_TRACE_POINTS
+#define CREATE_RUST_TRACE_POINTS
+#include "rust_binder_events.h"

drivers/android/binder/rust_binder_events.h

@@ -0,0 +1,36 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+/*
+ * Copyright (C) 2025 Google, Inc.
+ */
+
+#undef TRACE_SYSTEM
+#undef TRACE_INCLUDE_FILE
+#undef TRACE_INCLUDE_PATH
+#define TRACE_SYSTEM rust_binder
+#define TRACE_INCLUDE_FILE rust_binder_events
+#define TRACE_INCLUDE_PATH ../drivers/android/binder
+
+#if !defined(_RUST_BINDER_TRACE_H) || defined(TRACE_HEADER_MULTI_READ)
+#define _RUST_BINDER_TRACE_H
+
+#include <linux/tracepoint.h>
+
+TRACE_EVENT(rust_binder_ioctl,
+	TP_PROTO(unsigned int cmd, unsigned long arg),
+	TP_ARGS(cmd, arg),
+
+	TP_STRUCT__entry(
+		__field(unsigned int, cmd)
+		__field(unsigned long, arg)
+	),
+	TP_fast_assign(
+		__entry->cmd = cmd;
+		__entry->arg = arg;
+	),
+	TP_printk("cmd=0x%x arg=0x%lx", __entry->cmd, __entry->arg)
+);
+
+#endif /* _RUST_BINDER_TRACE_H */
+
+/* This part must be outside protection */
+#include <trace/define_trace.h>

drivers/android/binder/rust_binder_internal.h

@@ -0,0 +1,87 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/* rust_binder_internal.h
+ *
+ * This file contains internal data structures used by Rust Binder. Mostly,
+ * these are type definitions used only by binderfs or things that Rust Binder
+ * define and export to binderfs.
+ *
+ * It does not include things exported by binderfs to Rust Binder since this
+ * file is not included as input to bindgen.
+ *
+ * Copyright (C) 2025 Google LLC.
+ */
+
+#ifndef _LINUX_RUST_BINDER_INTERNAL_H
+#define _LINUX_RUST_BINDER_INTERNAL_H
+
+#define RUST_BINDERFS_SUPER_MAGIC	0x6c6f6f71
+
+#include <linux/seq_file.h>
+#include <uapi/linux/android/binder.h>
+#include <uapi/linux/android/binderfs.h>
+
+/*
+ * The internal data types in the Rust Binder driver are opaque to C, so we use
+ * void pointer typedefs for these types.
+ */
+typedef void *rust_binder_context;
+
+/**
+ * struct binder_device - information about a binder device node
+ * @minor:     the minor number used by this device
+ * @ctx:       the Rust Context used by this device, or null for binder-control
+ *
+ * This is used as the private data for files directly in binderfs, but not
+ * files in the binder_logs subdirectory. This struct owns a refcount on `ctx`
+ * and the entry for `minor` in `binderfs_minors`. For binder-control `ctx` is
+ * null.
+ */
+struct binder_device {
+	int minor;
+	rust_binder_context ctx;
+};
+
+int rust_binder_stats_show(struct seq_file *m, void *unused);
+int rust_binder_state_show(struct seq_file *m, void *unused);
+int rust_binder_transactions_show(struct seq_file *m, void *unused);
+int rust_binder_proc_show(struct seq_file *m, void *pid);
+
+extern const struct file_operations rust_binder_fops;
+rust_binder_context rust_binder_new_context(char *name);
+void rust_binder_remove_context(rust_binder_context device);
+
+/**
+ * binderfs_mount_opts - mount options for binderfs
+ * @max: maximum number of allocatable binderfs binder devices
+ * @stats_mode: enable binder stats in binderfs.
+ */
+struct binderfs_mount_opts {
+	int max;
+	int stats_mode;
+};
+
+/**
+ * binderfs_info - information about a binderfs mount
+ * @ipc_ns:         The ipc namespace the binderfs mount belongs to.
+ * @control_dentry: This records the dentry of this binderfs mount
+ *                  binder-control device.
+ * @root_uid:       uid that needs to be used when a new binder device is
+ *                  created.
+ * @root_gid:       gid that needs to be used when a new binder device is
+ *                  created.
+ * @mount_opts:     The mount options in use.
+ * @device_count:   The current number of allocated binder devices.
+ * @proc_log_dir:   Pointer to the directory dentry containing process-specific
+ *                  logs.
+ */
+struct binderfs_info {
+	struct ipc_namespace *ipc_ns;
+	struct dentry *control_dentry;
+	kuid_t root_uid;
+	kgid_t root_gid;
+	struct binderfs_mount_opts mount_opts;
+	int device_count;
+	struct dentry *proc_log_dir;
+};
+
+#endif /* _LINUX_RUST_BINDER_INTERNAL_H */

drivers/android/binder/rust_binder_main.rs

@@ -0,0 +1,627 @@
+// SPDX-License-Identifier: GPL-2.0
+
+// Copyright (C) 2025 Google LLC.
+
+//! Binder -- the Android IPC mechanism.
+#![recursion_limit = "256"]
+#![allow(
+    clippy::as_underscore,
+    clippy::ref_as_ptr,
+    clippy::ptr_as_ptr,
+    clippy::cast_lossless
+)]
+
+use kernel::{
+    bindings::{self, seq_file},
+    fs::File,
+    list::{ListArc, ListArcSafe, ListLinksSelfPtr, TryNewListArc},
+    prelude::*,
+    seq_file::SeqFile,
+    seq_print,
+    sync::poll::PollTable,
+    sync::Arc,
+    task::Pid,
+    transmute::AsBytes,
+    types::ForeignOwnable,
+    uaccess::UserSliceWriter,
+};
+
+use crate::{context::Context, page_range::Shrinker, process::Process, thread::Thread};
+
+use core::{
+    ptr::NonNull,
+    sync::atomic::{AtomicBool, AtomicUsize, Ordering},
+};
+
+mod allocation;
+mod context;
+mod deferred_close;
+mod defs;
+mod error;
+mod node;
+mod page_range;
+mod process;
+mod range_alloc;
+mod stats;
+mod thread;
+mod trace;
+mod transaction;
+
+#[allow(warnings)] // generated bindgen code
+mod binderfs {
+    use kernel::bindings::{dentry, inode};
+
+    extern "C" {
+        pub fn init_rust_binderfs() -> kernel::ffi::c_int;
+    }
+    extern "C" {
+        pub fn rust_binderfs_create_proc_file(
+            nodp: *mut inode,
+            pid: kernel::ffi::c_int,
+        ) -> *mut dentry;
+    }
+    extern "C" {
+        pub fn rust_binderfs_remove_file(dentry: *mut dentry);
+    }
+    pub type rust_binder_context = *mut kernel::ffi::c_void;
+    #[repr(C)]
+    #[derive(Copy, Clone)]
+    pub struct binder_device {
+        pub minor: kernel::ffi::c_int,
+        pub ctx: rust_binder_context,
+    }
+    impl Default for binder_device {
+        fn default() -> Self {
+            let mut s = ::core::mem::MaybeUninit::<Self>::uninit();
+            unsafe {
+                ::core::ptr::write_bytes(s.as_mut_ptr(), 0, 1);
+                s.assume_init()
+            }
+        }
+    }
+}
+
+module! {
+    type: BinderModule,
+    name: "rust_binder",
+    authors: ["Wedson Almeida Filho", "Alice Ryhl"],
+    description: "Android Binder",
+    license: "GPL",
+}
+
+fn next_debug_id() -> usize {
+    static NEXT_DEBUG_ID: AtomicUsize = AtomicUsize::new(0);
+
+    NEXT_DEBUG_ID.fetch_add(1, Ordering::Relaxed)
+}
+
+/// Provides a single place to write Binder return values via the
+/// supplied `UserSliceWriter`.
+pub(crate) struct BinderReturnWriter<'a> {
+    writer: UserSliceWriter,
+    thread: &'a Thread,
+}
+
+impl<'a> BinderReturnWriter<'a> {
+    fn new(writer: UserSliceWriter, thread: &'a Thread) -> Self {
+        BinderReturnWriter { writer, thread }
+    }
+
+    /// Write a return code back to user space.
+    /// Should be a `BR_` constant from [`defs`] e.g. [`defs::BR_TRANSACTION_COMPLETE`].
+    fn write_code(&mut self, code: u32) -> Result {
+        stats::GLOBAL_STATS.inc_br(code);
+        self.thread.process.stats.inc_br(code);
+        self.writer.write(&code)
+    }
+
+    /// Write something *other than* a return code to user space.
+    fn write_payload<T: AsBytes>(&mut self, payload: &T) -> Result {
+        self.writer.write(payload)
+    }
+
+    fn len(&self) -> usize {
+        self.writer.len()
+    }
+}
+
+/// Specifies how a type should be delivered to the read part of a BINDER_WRITE_READ ioctl.
+///
+/// When a value is pushed to the todo list for a process or thread, it is stored as a trait object
+/// with the type `Arc<dyn DeliverToRead>`. Trait objects are a Rust feature that lets you
+/// implement dynamic dispatch over many different types. This lets us store many different types
+/// in the todo list.
+trait DeliverToRead: ListArcSafe + Send + Sync {
+    /// Performs work. Returns true if remaining work items in the queue should be processed
+    /// immediately, or false if it should return to caller before processing additional work
+    /// items.
+    fn do_work(
+        self: DArc<Self>,
+        thread: &Thread,
+        writer: &mut BinderReturnWriter<'_>,
+    ) -> Result<bool>;
+
+    /// Cancels the given work item. This is called instead of [`DeliverToRead::do_work`] when work
+    /// won't be delivered.
+    fn cancel(self: DArc<Self>);
+
+    /// Should we use `wake_up_interruptible_sync` or `wake_up_interruptible` when scheduling this
+    /// work item?
+    ///
+    /// Generally only set to true for non-oneway transactions.
+    fn should_sync_wakeup(&self) -> bool;
+
+    fn debug_print(&self, m: &SeqFile, prefix: &str, transaction_prefix: &str) -> Result<()>;
+}
+
+// Wrapper around a `DeliverToRead` with linked list links.
+#[pin_data]
+struct DTRWrap<T: ?Sized> {
+    #[pin]
+    links: ListLinksSelfPtr<DTRWrap<dyn DeliverToRead>>,
+    #[pin]
+    wrapped: T,
+}
+kernel::list::impl_list_arc_safe! {
+    impl{T: ListArcSafe + ?Sized} ListArcSafe<0> for DTRWrap<T> {
+        tracked_by wrapped: T;
+    }
+}
+kernel::list::impl_list_item! {
+    impl ListItem<0> for DTRWrap<dyn DeliverToRead> {
+        using ListLinksSelfPtr { self.links };
+    }
+}
+
+impl<T: ?Sized> core::ops::Deref for DTRWrap<T> {
+    type Target = T;
+    fn deref(&self) -> &T {
+        &self.wrapped
+    }
+}
+
+type DArc<T> = kernel::sync::Arc<DTRWrap<T>>;
+type DLArc<T> = kernel::list::ListArc<DTRWrap<T>>;
+
+impl<T: ListArcSafe> DTRWrap<T> {
+    fn new(val: impl PinInit<T>) -> impl PinInit<Self> {
+        pin_init!(Self {
+            links <- ListLinksSelfPtr::new(),
+            wrapped <- val,
+        })
+    }
+
+    fn arc_try_new(val: T) -> Result<DLArc<T>, kernel::alloc::AllocError> {
+        ListArc::pin_init(
+            try_pin_init!(Self {
+                links <- ListLinksSelfPtr::new(),
+                wrapped: val,
+            }),
+            GFP_KERNEL,
+        )
+        .map_err(|_| kernel::alloc::AllocError)
+    }
+
+    fn arc_pin_init(init: impl PinInit<T>) -> Result<DLArc<T>, kernel::error::Error> {
+        ListArc::pin_init(
+            try_pin_init!(Self {
+                links <- ListLinksSelfPtr::new(),
+                wrapped <- init,
+            }),
+            GFP_KERNEL,
+        )
+    }
+}
+
+struct DeliverCode {
+    code: u32,
+    skip: AtomicBool,
+}
+
+kernel::list::impl_list_arc_safe! {
+    impl ListArcSafe<0> for DeliverCode { untracked; }
+}
+
+impl DeliverCode {
+    fn new(code: u32) -> Self {
+        Self {
+            code,
+            skip: AtomicBool::new(false),
+        }
+    }
+
+    /// Disable this DeliverCode and make it do nothing.
+    ///
+    /// This is used instead of removing it from the work list, since `LinkedList::remove` is
+    /// unsafe, whereas this method is not.
+    fn skip(&self) {
+        self.skip.store(true, Ordering::Relaxed);
+    }
+}
+
+impl DeliverToRead for DeliverCode {
+    fn do_work(
+        self: DArc<Self>,
+        _thread: &Thread,
+        writer: &mut BinderReturnWriter<'_>,
+    ) -> Result<bool> {
+        if !self.skip.load(Ordering::Relaxed) {
+            writer.write_code(self.code)?;
+        }
+        Ok(true)
+    }
+
+    fn cancel(self: DArc<Self>) {}
+
+    fn should_sync_wakeup(&self) -> bool {
+        false
+    }
+
+    fn debug_print(&self, m: &SeqFile, prefix: &str, _tprefix: &str) -> Result<()> {
+        seq_print!(m, "{}", prefix);
+        if self.skip.load(Ordering::Relaxed) {
+            seq_print!(m, "(skipped) ");
+        }
+        if self.code == defs::BR_TRANSACTION_COMPLETE {
+            seq_print!(m, "transaction complete\n");
+        } else {
+            seq_print!(m, "transaction error: {}\n", self.code);
+        }
+        Ok(())
+    }
+}
+
+fn ptr_align(value: usize) -> Option<usize> {
+    let size = core::mem::size_of::<usize>() - 1;
+    Some(value.checked_add(size)? & !size)
+}
+
+// SAFETY: We call register in `init`.
+static BINDER_SHRINKER: Shrinker = unsafe { Shrinker::new() };
+
+struct BinderModule {}
+
+impl kernel::Module for BinderModule {
+    fn init(_module: &'static kernel::ThisModule) -> Result<Self> {
+        // SAFETY: The module initializer never runs twice, so we only call this once.
+        unsafe { crate::context::CONTEXTS.init() };
+
+        pr_warn!("Loaded Rust Binder.");
+
+        BINDER_SHRINKER.register(kernel::c_str!("android-binder"))?;
+
+        // SAFETY: The module is being loaded, so we can initialize binderfs.
+        unsafe { kernel::error::to_result(binderfs::init_rust_binderfs())? };
+
+        Ok(Self {})
+    }
+}
+
+/// Makes the inner type Sync.
+#[repr(transparent)]
+pub struct AssertSync<T>(T);
+// SAFETY: Used only to insert `file_operations` into a global, which is safe.
+unsafe impl<T> Sync for AssertSync<T> {}
+
+/// File operations that rust_binderfs.c can use.
+#[no_mangle]
+#[used]
+pub static rust_binder_fops: AssertSync<kernel::bindings::file_operations> = {
+    // SAFETY: All zeroes is safe for the `file_operations` type.
+    let zeroed_ops = unsafe { core::mem::MaybeUninit::zeroed().assume_init() };
+
+    let ops = kernel::bindings::file_operations {
+        owner: THIS_MODULE.as_ptr(),
+        poll: Some(rust_binder_poll),
+        unlocked_ioctl: Some(rust_binder_unlocked_ioctl),
+        compat_ioctl: Some(rust_binder_compat_ioctl),
+        mmap: Some(rust_binder_mmap),
+        open: Some(rust_binder_open),
+        release: Some(rust_binder_release),
+        flush: Some(rust_binder_flush),
+        ..zeroed_ops
+    };
+    AssertSync(ops)
+};
+
+/// # Safety
+/// Only called by binderfs.
+#[no_mangle]
+unsafe extern "C" fn rust_binder_new_context(
+    name: *const kernel::ffi::c_char,
+) -> *mut kernel::ffi::c_void {
+    // SAFETY: The caller will always provide a valid c string here.
+    let name = unsafe { kernel::str::CStr::from_char_ptr(name) };
+    match Context::new(name) {
+        Ok(ctx) => Arc::into_foreign(ctx),
+        Err(_err) => core::ptr::null_mut(),
+    }
+}
+
+/// # Safety
+/// Only called by binderfs.
+#[no_mangle]
+unsafe extern "C" fn rust_binder_remove_context(device: *mut kernel::ffi::c_void) {
+    if !device.is_null() {
+        // SAFETY: The caller ensures that the `device` pointer came from a previous call to
+        // `rust_binder_new_device`.
+        let ctx = unsafe { Arc::<Context>::from_foreign(device) };
+        ctx.deregister();
+        drop(ctx);
+    }
+}
+
+/// # Safety
+/// Only called by binderfs.
+unsafe extern "C" fn rust_binder_open(
+    inode: *mut bindings::inode,
+    file_ptr: *mut bindings::file,
+) -> kernel::ffi::c_int {
+    // SAFETY: The `rust_binderfs.c` file ensures that `i_private` is set to a
+    // `struct binder_device`.
+    let device = unsafe { (*inode).i_private } as *const binderfs::binder_device;
+
+    assert!(!device.is_null());
+
+    // SAFETY: The `rust_binderfs.c` file ensures that `device->ctx` holds a binder context when
+    // using the rust binder fops.
+    let ctx = unsafe { Arc::<Context>::borrow((*device).ctx) };
+
+    // SAFETY: The caller provides a valid file pointer to a new `struct file`.
+    let file = unsafe { File::from_raw_file(file_ptr) };
+    let process = match Process::open(ctx, file) {
+        Ok(process) => process,
+        Err(err) => return err.to_errno(),
+    };
+
+    // SAFETY: This is an `inode` for a newly created binder file.
+    match unsafe { BinderfsProcFile::new(inode, process.task.pid()) } {
+        Ok(Some(file)) => process.inner.lock().binderfs_file = Some(file),
+        Ok(None) => { /* pid already exists */ }
+        Err(err) => return err.to_errno(),
+    }
+
+    // SAFETY: This file is associated with Rust binder, so we own the `private_data` field.
+    unsafe { (*file_ptr).private_data = process.into_foreign() };
+    0
+}
+
+/// # Safety
+/// Only called by binderfs.
+unsafe extern "C" fn rust_binder_release(
+    _inode: *mut bindings::inode,
+    file: *mut bindings::file,
+) -> kernel::ffi::c_int {
+    // SAFETY: We previously set `private_data` in `rust_binder_open`.
+    let process = unsafe { Arc::<Process>::from_foreign((*file).private_data) };
+    // SAFETY: The caller ensures that the file is valid.
+    let file = unsafe { File::from_raw_file(file) };
+    Process::release(process, file);
+    0
+}
+
+/// # Safety
+/// Only called by binderfs.
+unsafe extern "C" fn rust_binder_compat_ioctl(
+    file: *mut bindings::file,
+    cmd: kernel::ffi::c_uint,
+    arg: kernel::ffi::c_ulong,
+) -> kernel::ffi::c_long {
+    // SAFETY: We previously set `private_data` in `rust_binder_open`.
+    let f = unsafe { Arc::<Process>::borrow((*file).private_data) };
+    // SAFETY: The caller ensures that the file is valid.
+    match Process::compat_ioctl(f, unsafe { File::from_raw_file(file) }, cmd as _, arg as _) {
+        Ok(()) => 0,
+        Err(err) => err.to_errno() as isize,
+    }
+}
+
+/// # Safety
+/// Only called by binderfs.
+unsafe extern "C" fn rust_binder_unlocked_ioctl(
+    file: *mut bindings::file,
+    cmd: kernel::ffi::c_uint,
+    arg: kernel::ffi::c_ulong,
+) -> kernel::ffi::c_long {
+    // SAFETY: We previously set `private_data` in `rust_binder_open`.
+    let f = unsafe { Arc::<Process>::borrow((*file).private_data) };
+    // SAFETY: The caller ensures that the file is valid.
+    match Process::ioctl(f, unsafe { File::from_raw_file(file) }, cmd as _, arg as _) {
+        Ok(()) => 0,
+        Err(err) => err.to_errno() as isize,
+    }
+}
+
+/// # Safety
+/// Only called by binderfs.
+unsafe extern "C" fn rust_binder_mmap(
+    file: *mut bindings::file,
+    vma: *mut bindings::vm_area_struct,
+) -> kernel::ffi::c_int {
+    // SAFETY: We previously set `private_data` in `rust_binder_open`.
+    let f = unsafe { Arc::<Process>::borrow((*file).private_data) };
+    // SAFETY: The caller ensures that the vma is valid.
+    let area = unsafe { kernel::mm::virt::VmaNew::from_raw(vma) };
+    // SAFETY: The caller ensures that the file is valid.
+    match Process::mmap(f, unsafe { File::from_raw_file(file) }, area) {
+        Ok(()) => 0,
+        Err(err) => err.to_errno(),
+    }
+}
+
+/// # Safety
+/// Only called by binderfs.
+unsafe extern "C" fn rust_binder_poll(
+    file: *mut bindings::file,
+    wait: *mut bindings::poll_table_struct,
+) -> bindings::__poll_t {
+    // SAFETY: We previously set `private_data` in `rust_binder_open`.
+    let f = unsafe { Arc::<Process>::borrow((*file).private_data) };
+    // SAFETY: The caller ensures that the file is valid.
+    let fileref = unsafe { File::from_raw_file(file) };
+    // SAFETY: The caller ensures that the `PollTable` is valid.
+    match Process::poll(f, fileref, unsafe { PollTable::from_raw(wait) }) {
+        Ok(v) => v,
+        Err(_) => bindings::POLLERR,
+    }
+}
+
+/// # Safety
+/// Only called by binderfs.
+unsafe extern "C" fn rust_binder_flush(
+    file: *mut bindings::file,
+    _id: bindings::fl_owner_t,
+) -> kernel::ffi::c_int {
+    // SAFETY: We previously set `private_data` in `rust_binder_open`.
+    let f = unsafe { Arc::<Process>::borrow((*file).private_data) };
+    match Process::flush(f) {
+        Ok(()) => 0,
+        Err(err) => err.to_errno(),
+    }
+}
+
+/// # Safety
+/// Only called by binderfs.
+#[no_mangle]
+unsafe extern "C" fn rust_binder_stats_show(
+    ptr: *mut seq_file,
+    _: *mut kernel::ffi::c_void,
+) -> kernel::ffi::c_int {
+    // SAFETY: The caller ensures that the pointer is valid and exclusive for the duration in which
+    // this method is called.
+    let m = unsafe { SeqFile::from_raw(ptr) };
+    if let Err(err) = rust_binder_stats_show_impl(m) {
+        seq_print!(m, "failed to generate state: {:?}\n", err);
+    }
+    0
+}
+
+/// # Safety
+/// Only called by binderfs.
+#[no_mangle]
+unsafe extern "C" fn rust_binder_state_show(
+    ptr: *mut seq_file,
+    _: *mut kernel::ffi::c_void,
+) -> kernel::ffi::c_int {
+    // SAFETY: The caller ensures that the pointer is valid and exclusive for the duration in which
+    // this method is called.
+    let m = unsafe { SeqFile::from_raw(ptr) };
+    if let Err(err) = rust_binder_state_show_impl(m) {
+        seq_print!(m, "failed to generate state: {:?}\n", err);
+    }
+    0
+}
+
+/// # Safety
+/// Only called by binderfs.
+#[no_mangle]
+unsafe extern "C" fn rust_binder_proc_show(
+    ptr: *mut seq_file,
+    _: *mut kernel::ffi::c_void,
+) -> kernel::ffi::c_int {
+    // SAFETY: Accessing the private field of `seq_file` is okay.
+    let pid = (unsafe { (*ptr).private }) as usize as Pid;
+    // SAFETY: The caller ensures that the pointer is valid and exclusive for the duration in which
+    // this method is called.
+    let m = unsafe { SeqFile::from_raw(ptr) };
+    if let Err(err) = rust_binder_proc_show_impl(m, pid) {
+        seq_print!(m, "failed to generate state: {:?}\n", err);
+    }
+    0
+}
+
+/// # Safety
+/// Only called by binderfs.
+#[no_mangle]
+unsafe extern "C" fn rust_binder_transactions_show(
+    ptr: *mut seq_file,
+    _: *mut kernel::ffi::c_void,
+) -> kernel::ffi::c_int {
+    // SAFETY: The caller ensures that the pointer is valid and exclusive for the duration in which
+    // this method is called.
+    let m = unsafe { SeqFile::from_raw(ptr) };
+    if let Err(err) = rust_binder_transactions_show_impl(m) {
+        seq_print!(m, "failed to generate state: {:?}\n", err);
+    }
+    0
+}
+
+fn rust_binder_transactions_show_impl(m: &SeqFile) -> Result<()> {
+    seq_print!(m, "binder transactions:\n");
+    let contexts = context::get_all_contexts()?;
+    for ctx in contexts {
+        let procs = ctx.get_all_procs()?;
+        for proc in procs {
+            proc.debug_print(m, &ctx, false)?;
+            seq_print!(m, "\n");
+        }
+    }
+    Ok(())
+}
+
+fn rust_binder_stats_show_impl(m: &SeqFile) -> Result<()> {
+    seq_print!(m, "binder stats:\n");
+    stats::GLOBAL_STATS.debug_print("", m);
+    let contexts = context::get_all_contexts()?;
+    for ctx in contexts {
+        let procs = ctx.get_all_procs()?;
+        for proc in procs {
+            proc.debug_print_stats(m, &ctx)?;
+            seq_print!(m, "\n");
+        }
+    }
+    Ok(())
+}
+
+fn rust_binder_state_show_impl(m: &SeqFile) -> Result<()> {
+    seq_print!(m, "binder state:\n");
+    let contexts = context::get_all_contexts()?;
+    for ctx in contexts {
+        let procs = ctx.get_all_procs()?;
+        for proc in procs {
+            proc.debug_print(m, &ctx, true)?;
+            seq_print!(m, "\n");
+        }
+    }
+    Ok(())
+}
+
+fn rust_binder_proc_show_impl(m: &SeqFile, pid: Pid) -> Result<()> {
+    seq_print!(m, "binder proc state:\n");
+    let contexts = context::get_all_contexts()?;
+    for ctx in contexts {
+        let procs = ctx.get_procs_with_pid(pid)?;
+        for proc in procs {
+            proc.debug_print(m, &ctx, true)?;
+            seq_print!(m, "\n");
+        }
+    }
+    Ok(())
+}
+
+struct BinderfsProcFile(NonNull<bindings::dentry>);
+
+// SAFETY: Safe to drop any thread.
+unsafe impl Send for BinderfsProcFile {}
+
+impl BinderfsProcFile {
+    /// # Safety
+    ///
+    /// Takes an inode from a newly created binder file.
+    unsafe fn new(nodp: *mut bindings::inode, pid: i32) -> Result<Option<Self>> {
+        // SAFETY: The caller passes an `inode` for a newly created binder file.
+        let dentry = unsafe { binderfs::rust_binderfs_create_proc_file(nodp, pid) };
+        match kernel::error::from_err_ptr(dentry) {
+            Ok(dentry) => Ok(NonNull::new(dentry).map(Self)),
+            Err(err) if err == EEXIST => Ok(None),
+            Err(err) => Err(err),
+        }
+    }
+}
+
+impl Drop for BinderfsProcFile {
+    fn drop(&mut self) {
+        // SAFETY: This is a dentry from `rust_binderfs_remove_file` that has not been deleted yet.
+        unsafe { binderfs::rust_binderfs_remove_file(self.0.as_ptr()) };
+    }
+}

drivers/android/binder/rust_binderfs.c

@@ -0,0 +1,850 @@
+// SPDX-License-Identifier: GPL-2.0
+
+#include <linux/compiler_types.h>
+#include <linux/errno.h>
+#include <linux/fs.h>
+#include <linux/fsnotify.h>
+#include <linux/gfp.h>
+#include <linux/idr.h>
+#include <linux/init.h>
+#include <linux/ipc_namespace.h>
+#include <linux/kdev_t.h>
+#include <linux/kernel.h>
+#include <linux/list.h>
+#include <linux/namei.h>
+#include <linux/magic.h>
+#include <linux/major.h>
+#include <linux/miscdevice.h>
+#include <linux/module.h>
+#include <linux/mutex.h>
+#include <linux/mount.h>
+#include <linux/fs_parser.h>
+#include <linux/sched.h>
+#include <linux/seq_file.h>
+#include <linux/slab.h>
+#include <linux/spinlock_types.h>
+#include <linux/stddef.h>
+#include <linux/string.h>
+#include <linux/types.h>
+#include <linux/uaccess.h>
+#include <linux/user_namespace.h>
+#include <linux/xarray.h>
+#include <uapi/asm-generic/errno-base.h>
+#include <uapi/linux/android/binder.h>
+#include <uapi/linux/android/binderfs.h>
+
+#include "rust_binder.h"
+#include "rust_binder_internal.h"
+
+#define FIRST_INODE 1
+#define SECOND_INODE 2
+#define INODE_OFFSET 3
+#define BINDERFS_MAX_MINOR (1U << MINORBITS)
+/* Ensure that the initial ipc namespace always has devices available. */
+#define BINDERFS_MAX_MINOR_CAPPED (BINDERFS_MAX_MINOR - 4)
+
+DEFINE_SHOW_ATTRIBUTE(rust_binder_stats);
+DEFINE_SHOW_ATTRIBUTE(rust_binder_state);
+DEFINE_SHOW_ATTRIBUTE(rust_binder_transactions);
+DEFINE_SHOW_ATTRIBUTE(rust_binder_proc);
+
+char *rust_binder_devices_param = CONFIG_ANDROID_BINDER_DEVICES;
+module_param_named(rust_devices, rust_binder_devices_param, charp, 0444);
+
+static dev_t binderfs_dev;
+static DEFINE_MUTEX(binderfs_minors_mutex);
+static DEFINE_IDA(binderfs_minors);
+
+enum binderfs_param {
+	Opt_max,
+	Opt_stats_mode,
+};
+
+enum binderfs_stats_mode {
+	binderfs_stats_mode_unset,
+	binderfs_stats_mode_global,
+};
+
+struct binder_features {
+	bool oneway_spam_detection;
+	bool extended_error;
+	bool freeze_notification;
+};
+
+static const struct constant_table binderfs_param_stats[] = {
+	{ "global", binderfs_stats_mode_global },
+	{}
+};
+
+static const struct fs_parameter_spec binderfs_fs_parameters[] = {
+	fsparam_u32("max",	Opt_max),
+	fsparam_enum("stats",	Opt_stats_mode, binderfs_param_stats),
+	{}
+};
+
+static struct binder_features binder_features = {
+	.oneway_spam_detection = true,
+	.extended_error = true,
+	.freeze_notification = true,
+};
+
+static inline struct binderfs_info *BINDERFS_SB(const struct super_block *sb)
+{
+	return sb->s_fs_info;
+}
+
+/**
+ * binderfs_binder_device_create - allocate inode from super block of a
+ *                                 binderfs mount
+ * @ref_inode: inode from wich the super block will be taken
+ * @userp:     buffer to copy information about new device for userspace to
+ * @req:       struct binderfs_device as copied from userspace
+ *
+ * This function allocates a new binder_device and reserves a new minor
+ * number for it.
+ * Minor numbers are limited and tracked globally in binderfs_minors. The
+ * function will stash a struct binder_device for the specific binder
+ * device in i_private of the inode.
+ * It will go on to allocate a new inode from the super block of the
+ * filesystem mount, stash a struct binder_device in its i_private field
+ * and attach a dentry to that inode.
+ *
+ * Return: 0 on success, negative errno on failure
+ */
+static int binderfs_binder_device_create(struct inode *ref_inode,
+					 struct binderfs_device __user *userp,
+					 struct binderfs_device *req)
+{
+	int minor, ret;
+	struct dentry *dentry, *root;
+	struct binder_device *device = NULL;
+	rust_binder_context ctx = NULL;
+	struct inode *inode = NULL;
+	struct super_block *sb = ref_inode->i_sb;
+	struct binderfs_info *info = sb->s_fs_info;
+#if defined(CONFIG_IPC_NS)
+	bool use_reserve = (info->ipc_ns == &init_ipc_ns);
+#else
+	bool use_reserve = true;
+#endif
+
+	/* Reserve new minor number for the new device. */
+	mutex_lock(&binderfs_minors_mutex);
+	if (++info->device_count <= info->mount_opts.max)
+		minor = ida_alloc_max(&binderfs_minors,
+				      use_reserve ? BINDERFS_MAX_MINOR :
+						    BINDERFS_MAX_MINOR_CAPPED,
+				      GFP_KERNEL);
+	else
+		minor = -ENOSPC;
+	if (minor < 0) {
+		--info->device_count;
+		mutex_unlock(&binderfs_minors_mutex);
+		return minor;
+	}
+	mutex_unlock(&binderfs_minors_mutex);
+
+	ret = -ENOMEM;
+	device = kzalloc(sizeof(*device), GFP_KERNEL);
+	if (!device)
+		goto err;
+
+	req->name[BINDERFS_MAX_NAME] = '\0'; /* NUL-terminate */
+
+	ctx = rust_binder_new_context(req->name);
+	if (!ctx)
+		goto err;
+
+	inode = new_inode(sb);
+	if (!inode)
+		goto err;
+
+	inode->i_ino = minor + INODE_OFFSET;
+	simple_inode_init_ts(inode);
+	init_special_inode(inode, S_IFCHR | 0600,
+			   MKDEV(MAJOR(binderfs_dev), minor));
+	inode->i_fop = &rust_binder_fops;
+	inode->i_uid = info->root_uid;
+	inode->i_gid = info->root_gid;
+
+	req->major = MAJOR(binderfs_dev);
+	req->minor = minor;
+	device->ctx = ctx;
+	device->minor = minor;
+
+	if (userp && copy_to_user(userp, req, sizeof(*req))) {
+		ret = -EFAULT;
+		goto err;
+	}
+
+	root = sb->s_root;
+	inode_lock(d_inode(root));
+
+	/* look it up */
+	dentry = lookup_noperm(&QSTR(req->name), root);
+	if (IS_ERR(dentry)) {
+		inode_unlock(d_inode(root));
+		ret = PTR_ERR(dentry);
+		goto err;
+	}
+
+	if (d_really_is_positive(dentry)) {
+		/* already exists */
+		dput(dentry);
+		inode_unlock(d_inode(root));
+		ret = -EEXIST;
+		goto err;
+	}
+
+	inode->i_private = device;
+	d_instantiate(dentry, inode);
+	fsnotify_create(root->d_inode, dentry);
+	inode_unlock(d_inode(root));
+
+	return 0;
+
+err:
+	kfree(device);
+	rust_binder_remove_context(ctx);
+	mutex_lock(&binderfs_minors_mutex);
+	--info->device_count;
+	ida_free(&binderfs_minors, minor);
+	mutex_unlock(&binderfs_minors_mutex);
+	iput(inode);
+
+	return ret;
+}
+
+/**
+ * binder_ctl_ioctl - handle binder device node allocation requests
+ *
+ * The request handler for the binder-control device. All requests operate on
+ * the binderfs mount the binder-control device resides in:
+ * - BINDER_CTL_ADD
+ *   Allocate a new binder device.
+ *
+ * Return: %0 on success, negative errno on failure.
+ */
+static long binder_ctl_ioctl(struct file *file, unsigned int cmd,
+			     unsigned long arg)
+{
+	int ret = -EINVAL;
+	struct inode *inode = file_inode(file);
+	struct binderfs_device __user *device = (struct binderfs_device __user *)arg;
+	struct binderfs_device device_req;
+
+	switch (cmd) {
+	case BINDER_CTL_ADD:
+		ret = copy_from_user(&device_req, device, sizeof(device_req));
+		if (ret) {
+			ret = -EFAULT;
+			break;
+		}
+
+		ret = binderfs_binder_device_create(inode, device, &device_req);
+		break;
+	default:
+		break;
+	}
+
+	return ret;
+}
+
+static void binderfs_evict_inode(struct inode *inode)
+{
+	struct binder_device *device = inode->i_private;
+	struct binderfs_info *info = BINDERFS_SB(inode->i_sb);
+
+	clear_inode(inode);
+
+	if (!S_ISCHR(inode->i_mode) || !device)
+		return;
+
+	mutex_lock(&binderfs_minors_mutex);
+	--info->device_count;
+	ida_free(&binderfs_minors, device->minor);
+	mutex_unlock(&binderfs_minors_mutex);
+
+	/* ctx is null for binder-control, but this function ignores null pointers */
+	rust_binder_remove_context(device->ctx);
+
+	kfree(device);
+}
+
+static int binderfs_fs_context_parse_param(struct fs_context *fc,
+					   struct fs_parameter *param)
+{
+	int opt;
+	struct binderfs_mount_opts *ctx = fc->fs_private;
+	struct fs_parse_result result;
+
+	opt = fs_parse(fc, binderfs_fs_parameters, param, &result);
+	if (opt < 0)
+		return opt;
+
+	switch (opt) {
+	case Opt_max:
+		if (result.uint_32 > BINDERFS_MAX_MINOR)
+			return invalfc(fc, "Bad value for '%s'", param->key);
+
+		ctx->max = result.uint_32;
+		break;
+	case Opt_stats_mode:
+		if (!capable(CAP_SYS_ADMIN))
+			return -EPERM;
+
+		ctx->stats_mode = result.uint_32;
+		break;
+	default:
+		return invalfc(fc, "Unsupported parameter '%s'", param->key);
+	}
+
+	return 0;
+}
+
+static int binderfs_fs_context_reconfigure(struct fs_context *fc)
+{
+	struct binderfs_mount_opts *ctx = fc->fs_private;
+	struct binderfs_info *info = BINDERFS_SB(fc->root->d_sb);
+
+	if (info->mount_opts.stats_mode != ctx->stats_mode)
+		return invalfc(fc, "Binderfs stats mode cannot be changed during a remount");
+
+	info->mount_opts.stats_mode = ctx->stats_mode;
+	info->mount_opts.max = ctx->max;
+	return 0;
+}
+
+static int binderfs_show_options(struct seq_file *seq, struct dentry *root)
+{
+	struct binderfs_info *info = BINDERFS_SB(root->d_sb);
+
+	if (info->mount_opts.max <= BINDERFS_MAX_MINOR)
+		seq_printf(seq, ",max=%d", info->mount_opts.max);
+
+	switch (info->mount_opts.stats_mode) {
+	case binderfs_stats_mode_unset:
+		break;
+	case binderfs_stats_mode_global:
+		seq_puts(seq, ",stats=global");
+		break;
+	}
+
+	return 0;
+}
+
+static const struct super_operations binderfs_super_ops = {
+	.evict_inode    = binderfs_evict_inode,
+	.show_options	= binderfs_show_options,
+	.statfs         = simple_statfs,
+};
+
+static inline bool is_binderfs_control_device(const struct dentry *dentry)
+{
+	struct binderfs_info *info = dentry->d_sb->s_fs_info;
+
+	return info->control_dentry == dentry;
+}
+
+static int binderfs_rename(struct mnt_idmap *idmap,
+			   struct inode *old_dir, struct dentry *old_dentry,
+			   struct inode *new_dir, struct dentry *new_dentry,
+			   unsigned int flags)
+{
+	if (is_binderfs_control_device(old_dentry) ||
+	    is_binderfs_control_device(new_dentry))
+		return -EPERM;
+
+	return simple_rename(idmap, old_dir, old_dentry, new_dir,
+			     new_dentry, flags);
+}
+
+static int binderfs_unlink(struct inode *dir, struct dentry *dentry)
+{
+	if (is_binderfs_control_device(dentry))
+		return -EPERM;
+
+	return simple_unlink(dir, dentry);
+}
+
+static const struct file_operations binder_ctl_fops = {
+	.owner		= THIS_MODULE,
+	.open		= nonseekable_open,
+	.unlocked_ioctl	= binder_ctl_ioctl,
+	.compat_ioctl	= binder_ctl_ioctl,
+	.llseek		= noop_llseek,
+};
+
+/**
+ * binderfs_binder_ctl_create - create a new binder-control device
+ * @sb: super block of the binderfs mount
+ *
+ * This function creates a new binder-control device node in the binderfs mount
+ * referred to by @sb.
+ *
+ * Return: 0 on success, negative errno on failure
+ */
+static int binderfs_binder_ctl_create(struct super_block *sb)
+{
+	int minor, ret;
+	struct dentry *dentry;
+	struct binder_device *device;
+	struct inode *inode = NULL;
+	struct dentry *root = sb->s_root;
+	struct binderfs_info *info = sb->s_fs_info;
+#if defined(CONFIG_IPC_NS)
+	bool use_reserve = (info->ipc_ns == &init_ipc_ns);
+#else
+	bool use_reserve = true;
+#endif
+
+	device = kzalloc(sizeof(*device), GFP_KERNEL);
+	if (!device)
+		return -ENOMEM;
+
+	/* If we have already created a binder-control node, return. */
+	if (info->control_dentry) {
+		ret = 0;
+		goto out;
+	}
+
+	ret = -ENOMEM;
+	inode = new_inode(sb);
+	if (!inode)
+		goto out;
+
+	/* Reserve a new minor number for the new device. */
+	mutex_lock(&binderfs_minors_mutex);
+	minor = ida_alloc_max(&binderfs_minors,
+			      use_reserve ? BINDERFS_MAX_MINOR :
+					    BINDERFS_MAX_MINOR_CAPPED,
+			      GFP_KERNEL);
+	mutex_unlock(&binderfs_minors_mutex);
+	if (minor < 0) {
+		ret = minor;
+		goto out;
+	}
+
+	inode->i_ino = SECOND_INODE;
+	simple_inode_init_ts(inode);
+	init_special_inode(inode, S_IFCHR | 0600,
+			   MKDEV(MAJOR(binderfs_dev), minor));
+	inode->i_fop = &binder_ctl_fops;
+	inode->i_uid = info->root_uid;
+	inode->i_gid = info->root_gid;
+
+	device->minor = minor;
+	device->ctx = NULL;
+
+	dentry = d_alloc_name(root, "binder-control");
+	if (!dentry)
+		goto out;
+
+	inode->i_private = device;
+	info->control_dentry = dentry;
+	d_add(dentry, inode);
+
+	return 0;
+
+out:
+	kfree(device);
+	iput(inode);
+
+	return ret;
+}
+
+static const struct inode_operations binderfs_dir_inode_operations = {
+	.lookup = simple_lookup,
+	.rename = binderfs_rename,
+	.unlink = binderfs_unlink,
+};
+
+static struct inode *binderfs_make_inode(struct super_block *sb, int mode)
+{
+	struct inode *ret;
+
+	ret = new_inode(sb);
+	if (ret) {
+		ret->i_ino = iunique(sb, BINDERFS_MAX_MINOR + INODE_OFFSET);
+		ret->i_mode = mode;
+		simple_inode_init_ts(ret);
+	}
+	return ret;
+}
+
+static struct dentry *binderfs_create_dentry(struct dentry *parent,
+					     const char *name)
+{
+	struct dentry *dentry;
+
+	dentry = lookup_noperm(&QSTR(name), parent);
+	if (IS_ERR(dentry))
+		return dentry;
+
+	/* Return error if the file/dir already exists. */
+	if (d_really_is_positive(dentry)) {
+		dput(dentry);
+		return ERR_PTR(-EEXIST);
+	}
+
+	return dentry;
+}
+
+void rust_binderfs_remove_file(struct dentry *dentry)
+{
+	struct inode *parent_inode;
+
+	parent_inode = d_inode(dentry->d_parent);
+	inode_lock(parent_inode);
+	if (simple_positive(dentry)) {
+		dget(dentry);
+		simple_unlink(parent_inode, dentry);
+		d_delete(dentry);
+		dput(dentry);
+	}
+	inode_unlock(parent_inode);
+}
+
+static struct dentry *rust_binderfs_create_file(struct dentry *parent, const char *name,
+						const struct file_operations *fops,
+						void *data)
+{
+	struct dentry *dentry;
+	struct inode *new_inode, *parent_inode;
+	struct super_block *sb;
+
+	parent_inode = d_inode(parent);
+	inode_lock(parent_inode);
+
+	dentry = binderfs_create_dentry(parent, name);
+	if (IS_ERR(dentry))
+		goto out;
+
+	sb = parent_inode->i_sb;
+	new_inode = binderfs_make_inode(sb, S_IFREG | 0444);
+	if (!new_inode) {
+		dput(dentry);
+		dentry = ERR_PTR(-ENOMEM);
+		goto out;
+	}
+
+	new_inode->i_fop = fops;
+	new_inode->i_private = data;
+	d_instantiate(dentry, new_inode);
+	fsnotify_create(parent_inode, dentry);
+
+out:
+	inode_unlock(parent_inode);
+	return dentry;
+}
+
+struct dentry *rust_binderfs_create_proc_file(struct inode *nodp, int pid)
+{
+	struct binderfs_info *info = nodp->i_sb->s_fs_info;
+	struct dentry *dir = info->proc_log_dir;
+	char strbuf[20 + 1];
+	void *data = (void *)(unsigned long) pid;
+
+	if (!dir)
+		return NULL;
+
+	snprintf(strbuf, sizeof(strbuf), "%u", pid);
+	return rust_binderfs_create_file(dir, strbuf, &rust_binder_proc_fops, data);
+}
+
+static struct dentry *binderfs_create_dir(struct dentry *parent,
+					  const char *name)
+{
+	struct dentry *dentry;
+	struct inode *new_inode, *parent_inode;
+	struct super_block *sb;
+
+	parent_inode = d_inode(parent);
+	inode_lock(parent_inode);
+
+	dentry = binderfs_create_dentry(parent, name);
+	if (IS_ERR(dentry))
+		goto out;
+
+	sb = parent_inode->i_sb;
+	new_inode = binderfs_make_inode(sb, S_IFDIR | 0755);
+	if (!new_inode) {
+		dput(dentry);
+		dentry = ERR_PTR(-ENOMEM);
+		goto out;
+	}
+
+	new_inode->i_fop = &simple_dir_operations;
+	new_inode->i_op = &simple_dir_inode_operations;
+
+	set_nlink(new_inode, 2);
+	d_instantiate(dentry, new_inode);
+	inc_nlink(parent_inode);
+	fsnotify_mkdir(parent_inode, dentry);
+
+out:
+	inode_unlock(parent_inode);
+	return dentry;
+}
+
+static int binder_features_show(struct seq_file *m, void *unused)
+{
+	bool *feature = m->private;
+
+	seq_printf(m, "%d\n", *feature);
+
+	return 0;
+}
+DEFINE_SHOW_ATTRIBUTE(binder_features);
+
+static int init_binder_features(struct super_block *sb)
+{
+	struct dentry *dentry, *dir;
+
+	dir = binderfs_create_dir(sb->s_root, "features");
+	if (IS_ERR(dir))
+		return PTR_ERR(dir);
+
+	dentry = rust_binderfs_create_file(dir, "oneway_spam_detection",
+				      &binder_features_fops,
+				      &binder_features.oneway_spam_detection);
+	if (IS_ERR(dentry))
+		return PTR_ERR(dentry);
+
+	dentry = rust_binderfs_create_file(dir, "extended_error",
+				      &binder_features_fops,
+				      &binder_features.extended_error);
+	if (IS_ERR(dentry))
+		return PTR_ERR(dentry);
+
+	dentry = rust_binderfs_create_file(dir, "freeze_notification",
+				      &binder_features_fops,
+				      &binder_features.freeze_notification);
+	if (IS_ERR(dentry))
+		return PTR_ERR(dentry);
+
+	return 0;
+}
+
+static int init_binder_logs(struct super_block *sb)
+{
+	struct dentry *binder_logs_root_dir, *dentry, *proc_log_dir;
+	struct binderfs_info *info;
+	int ret = 0;
+
+	binder_logs_root_dir = binderfs_create_dir(sb->s_root,
+						   "binder_logs");
+	if (IS_ERR(binder_logs_root_dir)) {
+		ret = PTR_ERR(binder_logs_root_dir);
+		goto out;
+	}
+
+	dentry = rust_binderfs_create_file(binder_logs_root_dir, "stats",
+				      &rust_binder_stats_fops, NULL);
+	if (IS_ERR(dentry)) {
+		ret = PTR_ERR(dentry);
+		goto out;
+	}
+
+	dentry = rust_binderfs_create_file(binder_logs_root_dir, "state",
+				      &rust_binder_state_fops, NULL);
+	if (IS_ERR(dentry)) {
+		ret = PTR_ERR(dentry);
+		goto out;
+	}
+
+	dentry = rust_binderfs_create_file(binder_logs_root_dir, "transactions",
+				      &rust_binder_transactions_fops, NULL);
+	if (IS_ERR(dentry)) {
+		ret = PTR_ERR(dentry);
+		goto out;
+	}
+
+	proc_log_dir = binderfs_create_dir(binder_logs_root_dir, "proc");
+	if (IS_ERR(proc_log_dir)) {
+		ret = PTR_ERR(proc_log_dir);
+		goto out;
+	}
+	info = sb->s_fs_info;
+	info->proc_log_dir = proc_log_dir;
+
+out:
+	return ret;
+}
+
+static int binderfs_fill_super(struct super_block *sb, struct fs_context *fc)
+{
+	int ret;
+	struct binderfs_info *info;
+	struct binderfs_mount_opts *ctx = fc->fs_private;
+	struct inode *inode = NULL;
+	struct binderfs_device device_info = {};
+	const char *name;
+	size_t len;
+
+	sb->s_blocksize = PAGE_SIZE;
+	sb->s_blocksize_bits = PAGE_SHIFT;
+
+	/*
+	 * The binderfs filesystem can be mounted by userns root in a
+	 * non-initial userns. By default such mounts have the SB_I_NODEV flag
+	 * set in s_iflags to prevent security issues where userns root can
+	 * just create random device nodes via mknod() since it owns the
+	 * filesystem mount. But binderfs does not allow to create any files
+	 * including devices nodes. The only way to create binder devices nodes
+	 * is through the binder-control device which userns root is explicitly
+	 * allowed to do. So removing the SB_I_NODEV flag from s_iflags is both
+	 * necessary and safe.
+	 */
+	sb->s_iflags &= ~SB_I_NODEV;
+	sb->s_iflags |= SB_I_NOEXEC;
+	sb->s_magic = RUST_BINDERFS_SUPER_MAGIC;
+	sb->s_op = &binderfs_super_ops;
+	sb->s_time_gran = 1;
+
+	sb->s_fs_info = kzalloc(sizeof(struct binderfs_info), GFP_KERNEL);
+	if (!sb->s_fs_info)
+		return -ENOMEM;
+	info = sb->s_fs_info;
+
+	info->ipc_ns = get_ipc_ns(current->nsproxy->ipc_ns);
+
+	info->root_gid = make_kgid(sb->s_user_ns, 0);
+	if (!gid_valid(info->root_gid))
+		info->root_gid = GLOBAL_ROOT_GID;
+	info->root_uid = make_kuid(sb->s_user_ns, 0);
+	if (!uid_valid(info->root_uid))
+		info->root_uid = GLOBAL_ROOT_UID;
+	info->mount_opts.max = ctx->max;
+	info->mount_opts.stats_mode = ctx->stats_mode;
+
+	inode = new_inode(sb);
+	if (!inode)
+		return -ENOMEM;
+
+	inode->i_ino = FIRST_INODE;
+	inode->i_fop = &simple_dir_operations;
+	inode->i_mode = S_IFDIR | 0755;
+	simple_inode_init_ts(inode);
+	inode->i_op = &binderfs_dir_inode_operations;
+	set_nlink(inode, 2);
+
+	sb->s_root = d_make_root(inode);
+	if (!sb->s_root)
+		return -ENOMEM;
+
+	ret = binderfs_binder_ctl_create(sb);
+	if (ret)
+		return ret;
+
+	name = rust_binder_devices_param;
+	for (len = strcspn(name, ","); len > 0; len = strcspn(name, ",")) {
+		strscpy(device_info.name, name, len + 1);
+		ret = binderfs_binder_device_create(inode, NULL, &device_info);
+		if (ret)
+			return ret;
+		name += len;
+		if (*name == ',')
+			name++;
+	}
+
+	ret = init_binder_features(sb);
+	if (ret)
+		return ret;
+
+	if (info->mount_opts.stats_mode == binderfs_stats_mode_global)
+		return init_binder_logs(sb);
+
+	return 0;
+}
+
+static int binderfs_fs_context_get_tree(struct fs_context *fc)
+{
+	return get_tree_nodev(fc, binderfs_fill_super);
+}
+
+static void binderfs_fs_context_free(struct fs_context *fc)
+{
+	struct binderfs_mount_opts *ctx = fc->fs_private;
+
+	kfree(ctx);
+}
+
+static const struct fs_context_operations binderfs_fs_context_ops = {
+	.free		= binderfs_fs_context_free,
+	.get_tree	= binderfs_fs_context_get_tree,
+	.parse_param	= binderfs_fs_context_parse_param,
+	.reconfigure	= binderfs_fs_context_reconfigure,
+};
+
+static int binderfs_init_fs_context(struct fs_context *fc)
+{
+	struct binderfs_mount_opts *ctx;
+
+	ctx = kzalloc(sizeof(struct binderfs_mount_opts), GFP_KERNEL);
+	if (!ctx)
+		return -ENOMEM;
+
+	ctx->max = BINDERFS_MAX_MINOR;
+	ctx->stats_mode = binderfs_stats_mode_unset;
+
+	fc->fs_private = ctx;
+	fc->ops = &binderfs_fs_context_ops;
+
+	return 0;
+}
+
+static void binderfs_kill_super(struct super_block *sb)
+{
+	struct binderfs_info *info = sb->s_fs_info;
+
+	/*
+	 * During inode eviction struct binderfs_info is needed.
+	 * So first wipe the super_block then free struct binderfs_info.
+	 */
+	kill_litter_super(sb);
+
+	if (info && info->ipc_ns)
+		put_ipc_ns(info->ipc_ns);
+
+	kfree(info);
+}
+
+static struct file_system_type binder_fs_type = {
+	.name			= "binder",
+	.init_fs_context	= binderfs_init_fs_context,
+	.parameters		= binderfs_fs_parameters,
+	.kill_sb		= binderfs_kill_super,
+	.fs_flags		= FS_USERNS_MOUNT,
+};
+
+int init_rust_binderfs(void)
+{
+	int ret;
+	const char *name;
+	size_t len;
+
+	/* Verify that the default binderfs device names are valid. */
+	name = rust_binder_devices_param;
+	for (len = strcspn(name, ","); len > 0; len = strcspn(name, ",")) {
+		if (len > BINDERFS_MAX_NAME)
+			return -E2BIG;
+		name += len;
+		if (*name == ',')
+			name++;
+	}
+
+	/* Allocate new major number for binderfs. */
+	ret = alloc_chrdev_region(&binderfs_dev, 0, BINDERFS_MAX_MINOR,
+				  "rust_binder");
+	if (ret)
+		return ret;
+
+	ret = register_filesystem(&binder_fs_type);
+	if (ret) {
+		unregister_chrdev_region(binderfs_dev, BINDERFS_MAX_MINOR);
+		return ret;
+	}
+
+	return ret;
+}

drivers/android/binder/stats.rs

@@ -0,0 +1,89 @@
+// SPDX-License-Identifier: GPL-2.0
+
+// Copyright (C) 2025 Google LLC.
+
+//! Keep track of statistics for binder_logs.
+
+use crate::defs::*;
+use core::sync::atomic::{AtomicU32, Ordering::Relaxed};
+use kernel::{ioctl::_IOC_NR, seq_file::SeqFile, seq_print};
+
+const BC_COUNT: usize = _IOC_NR(BC_REPLY_SG) as usize + 1;
+const BR_COUNT: usize = _IOC_NR(BR_TRANSACTION_PENDING_FROZEN) as usize + 1;
+
+pub(crate) static GLOBAL_STATS: BinderStats = BinderStats::new();
+
+pub(crate) struct BinderStats {
+    bc: [AtomicU32; BC_COUNT],
+    br: [AtomicU32; BR_COUNT],
+}
+
+impl BinderStats {
+    pub(crate) const fn new() -> Self {
+        #[expect(clippy::declare_interior_mutable_const)]
+        const ZERO: AtomicU32 = AtomicU32::new(0);
+
+        Self {
+            bc: [ZERO; BC_COUNT],
+            br: [ZERO; BR_COUNT],
+        }
+    }
+
+    pub(crate) fn inc_bc(&self, bc: u32) {
+        let idx = _IOC_NR(bc) as usize;
+        if let Some(bc_ref) = self.bc.get(idx) {
+            bc_ref.fetch_add(1, Relaxed);
+        }
+    }
+
+    pub(crate) fn inc_br(&self, br: u32) {
+        let idx = _IOC_NR(br) as usize;
+        if let Some(br_ref) = self.br.get(idx) {
+            br_ref.fetch_add(1, Relaxed);
+        }
+    }
+
+    pub(crate) fn debug_print(&self, prefix: &str, m: &SeqFile) {
+        for (i, cnt) in self.bc.iter().enumerate() {
+            let cnt = cnt.load(Relaxed);
+            if cnt > 0 {
+                seq_print!(m, "{}{}: {}\n", prefix, command_string(i), cnt);
+            }
+        }
+        for (i, cnt) in self.br.iter().enumerate() {
+            let cnt = cnt.load(Relaxed);
+            if cnt > 0 {
+                seq_print!(m, "{}{}: {}\n", prefix, return_string(i), cnt);
+            }
+        }
+    }
+}
+
+mod strings {
+    use core::str::from_utf8_unchecked;
+    use kernel::str::CStr;
+
+    extern "C" {
+        static binder_command_strings: [*const u8; super::BC_COUNT];
+        static binder_return_strings: [*const u8; super::BR_COUNT];
+    }
+
+    pub(super) fn command_string(i: usize) -> &'static str {
+        // SAFETY: Accessing `binder_command_strings` is always safe.
+        let c_str_ptr = unsafe { binder_command_strings[i] };
+        // SAFETY: The `binder_command_strings` array only contains nul-terminated strings.
+        let bytes = unsafe { CStr::from_char_ptr(c_str_ptr) }.as_bytes();
+        // SAFETY: The `binder_command_strings` array only contains strings with ascii-chars.
+        unsafe { from_utf8_unchecked(bytes) }
+    }
+
+    pub(super) fn return_string(i: usize) -> &'static str {
+        // SAFETY: Accessing `binder_return_strings` is always safe.
+        let c_str_ptr = unsafe { binder_return_strings[i] };
+        // SAFETY: The `binder_command_strings` array only contains nul-terminated strings.
+        let bytes = unsafe { CStr::from_char_ptr(c_str_ptr) }.as_bytes();
+        // SAFETY: The `binder_command_strings` array only contains strings with ascii-chars.
+        unsafe { from_utf8_unchecked(bytes) }
+    }
+}
+use strings::{command_string, return_string};

drivers/android/binder/trace.rs

@@ -0,0 +1,16 @@
+// SPDX-License-Identifier: GPL-2.0
+
+// Copyright (C) 2025 Google LLC.
+
+use kernel::ffi::{c_uint, c_ulong};
+use kernel::tracepoint::declare_trace;
+
+declare_trace! {
+    unsafe fn rust_binder_ioctl(cmd: c_uint, arg: c_ulong);
+}
+
+#[inline]
+pub(crate) fn trace_ioctl(cmd: u32, arg: usize) {
+    // SAFETY: Always safe to call.
+    unsafe { rust_binder_ioctl(cmd, arg as c_ulong) }
+}

drivers/android/binder/transaction.rs

@@ -0,0 +1,456 @@
+// SPDX-License-Identifier: GPL-2.0
+
+// Copyright (C) 2025 Google LLC.
+
+use core::sync::atomic::{AtomicBool, Ordering};
+use kernel::{
+    prelude::*,
+    seq_file::SeqFile,
+    seq_print,
+    sync::{Arc, SpinLock},
+    task::Kuid,
+    time::{Instant, Monotonic},
+    types::ScopeGuard,
+};
+
+use crate::{
+    allocation::{Allocation, TranslatedFds},
+    defs::*,
+    error::{BinderError, BinderResult},
+    node::{Node, NodeRef},
+    process::{Process, ProcessInner},
+    ptr_align,
+    thread::{PushWorkRes, Thread},
+    BinderReturnWriter, DArc, DLArc, DTRWrap, DeliverToRead,
+};
+
+#[pin_data(PinnedDrop)]
+pub(crate) struct Transaction {
+    pub(crate) debug_id: usize,
+    target_node: Option<DArc<Node>>,
+    pub(crate) from_parent: Option<DArc<Transaction>>,
+    pub(crate) from: Arc<Thread>,
+    pub(crate) to: Arc<Process>,
+    #[pin]
+    allocation: SpinLock<Option<Allocation>>,
+    is_outstanding: AtomicBool,
+    code: u32,
+    pub(crate) flags: u32,
+    data_size: usize,
+    offsets_size: usize,
+    data_address: usize,
+    sender_euid: Kuid,
+    txn_security_ctx_off: Option<usize>,
+    pub(crate) oneway_spam_detected: bool,
+    start_time: Instant<Monotonic>,
+}
+
+kernel::list::impl_list_arc_safe! {
+    impl ListArcSafe<0> for Transaction { untracked; }
+}
+
+impl Transaction {
+    pub(crate) fn new(
+        node_ref: NodeRef,
+        from_parent: Option<DArc<Transaction>>,
+        from: &Arc<Thread>,
+        tr: &BinderTransactionDataSg,
+    ) -> BinderResult<DLArc<Self>> {
+        let debug_id = super::next_debug_id();
+        let trd = &tr.transaction_data;
+        let allow_fds = node_ref.node.flags & FLAT_BINDER_FLAG_ACCEPTS_FDS != 0;
+        let txn_security_ctx = node_ref.node.flags & FLAT_BINDER_FLAG_TXN_SECURITY_CTX != 0;
+        let mut txn_security_ctx_off = if txn_security_ctx { Some(0) } else { None };
+        let to = node_ref.node.owner.clone();
+        let mut alloc = match from.copy_transaction_data(
+            to.clone(),
+            tr,
+            debug_id,
+            allow_fds,
+            txn_security_ctx_off.as_mut(),
+        ) {
+            Ok(alloc) => alloc,
+            Err(err) => {
+                if !err.is_dead() {
+                    pr_warn!("Failure in copy_transaction_data: {:?}", err);
+                }
+                return Err(err);
+            }
+        };
+        let oneway_spam_detected = alloc.oneway_spam_detected;
+        if trd.flags & TF_ONE_WAY != 0 {
+            if from_parent.is_some() {
+                pr_warn!("Oneway transaction should not be in a transaction stack.");
+                return Err(EINVAL.into());
+            }
+            alloc.set_info_oneway_node(node_ref.node.clone());
+        }
+        if trd.flags & TF_CLEAR_BUF != 0 {
+            alloc.set_info_clear_on_drop();
+        }
+        let target_node = node_ref.node.clone();
+        alloc.set_info_target_node(node_ref);
+        let data_address = alloc.ptr;
+
+        Ok(DTRWrap::arc_pin_init(pin_init!(Transaction {
+            debug_id,
+            target_node: Some(target_node),
+            from_parent,
+            sender_euid: from.process.task.euid(),
+            from: from.clone(),
+            to,
+            code: trd.code,
+            flags: trd.flags,
+            data_size: trd.data_size as _,
+            offsets_size: trd.offsets_size as _,
+            data_address,
+            allocation <- kernel::new_spinlock!(Some(alloc.success()), "Transaction::new"),
+            is_outstanding: AtomicBool::new(false),
+            txn_security_ctx_off,
+            oneway_spam_detected,
+            start_time: Instant::now(),
+        }))?)
+    }
+
+    pub(crate) fn new_reply(
+        from: &Arc<Thread>,
+        to: Arc<Process>,
+        tr: &BinderTransactionDataSg,
+        allow_fds: bool,
+    ) -> BinderResult<DLArc<Self>> {
+        let debug_id = super::next_debug_id();
+        let trd = &tr.transaction_data;
+        let mut alloc = match from.copy_transaction_data(to.clone(), tr, debug_id, allow_fds, None)
+        {
+            Ok(alloc) => alloc,
+            Err(err) => {
+                pr_warn!("Failure in copy_transaction_data: {:?}", err);
+                return Err(err);
+            }
+        };
+        let oneway_spam_detected = alloc.oneway_spam_detected;
+        if trd.flags & TF_CLEAR_BUF != 0 {
+            alloc.set_info_clear_on_drop();
+        }
+        Ok(DTRWrap::arc_pin_init(pin_init!(Transaction {
+            debug_id,
+            target_node: None,
+            from_parent: None,
+            sender_euid: from.process.task.euid(),
+            from: from.clone(),
+            to,
+            code: trd.code,
+            flags: trd.flags,
+            data_size: trd.data_size as _,
+            offsets_size: trd.offsets_size as _,
+            data_address: alloc.ptr,
+            allocation <- kernel::new_spinlock!(Some(alloc.success()), "Transaction::new"),
+            is_outstanding: AtomicBool::new(false),
+            txn_security_ctx_off: None,
+            oneway_spam_detected,
+            start_time: Instant::now(),
+        }))?)
+    }
+
+    #[inline(never)]
+    pub(crate) fn debug_print_inner(&self, m: &SeqFile, prefix: &str) {
+        seq_print!(
+            m,
+            "{}{}: from {}:{} to {} code {:x} flags {:x} elapsed {}ms",
+            prefix,
+            self.debug_id,
+            self.from.process.task.pid(),
+            self.from.id,
+            self.to.task.pid(),
+            self.code,
+            self.flags,
+            self.start_time.elapsed().as_millis(),
+        );
+        if let Some(target_node) = &self.target_node {
+            seq_print!(m, " node {}", target_node.debug_id);
+        }
+        seq_print!(m, " size {}:{}\n", self.data_size, self.offsets_size);
+    }
+
+    /// Determines if the transaction is stacked on top of the given transaction.
+    pub(crate) fn is_stacked_on(&self, onext: &Option<DArc<Self>>) -> bool {
+        match (&self.from_parent, onext) {
+            (None, None) => true,
+            (Some(from_parent), Some(next)) => Arc::ptr_eq(from_parent, next),
+            _ => false,
+        }
+    }
+
+    /// Returns a pointer to the next transaction on the transaction stack, if there is one.
+    pub(crate) fn clone_next(&self) -> Option<DArc<Self>> {
+        Some(self.from_parent.as_ref()?.clone())
+    }
+
+    /// Searches in the transaction stack for a thread that belongs to the target process. This is
+    /// useful when finding a target for a new transaction: if the node belongs to a process that
+    /// is already part of the transaction stack, we reuse the thread.
+    fn find_target_thread(&self) -> Option<Arc<Thread>> {
+        let mut it = &self.from_parent;
+        while let Some(transaction) = it {
+            if Arc::ptr_eq(&transaction.from.process, &self.to) {
+                return Some(transaction.from.clone());
+            }
+            it = &transaction.from_parent;
+        }
+        None
+    }
+
+    /// Searches in the transaction stack for a transaction originating at the given thread.
+    pub(crate) fn find_from(&self, thread: &Thread) -> Option<&DArc<Transaction>> {
+        let mut it = &self.from_parent;
+        while let Some(transaction) = it {
+            if core::ptr::eq(thread, transaction.from.as_ref()) {
+                return Some(transaction);
+            }
+
+            it = &transaction.from_parent;
+        }
+        None
+    }
+
+    pub(crate) fn set_outstanding(&self, to_process: &mut ProcessInner) {
+        // No race because this method is only called once.
+        if !self.is_outstanding.load(Ordering::Relaxed) {
+            self.is_outstanding.store(true, Ordering::Relaxed);
+            to_process.add_outstanding_txn();
+        }
+    }
+
+    /// Decrement `outstanding_txns` in `to` if it hasn't already been decremented.
+    fn drop_outstanding_txn(&self) {
+        // No race because this is called at most twice, and one of the calls are in the
+        // destructor, which is guaranteed to not race with any other operations on the
+        // transaction. It also cannot race with `set_outstanding`, since submission happens
+        // before delivery.
+        if self.is_outstanding.load(Ordering::Relaxed) {
+            self.is_outstanding.store(false, Ordering::Relaxed);
+            self.to.drop_outstanding_txn();
+        }
+    }
+
+    /// Submits the transaction to a work queue. Uses a thread if there is one in the transaction
+    /// stack, otherwise uses the destination process.
+    ///
+    /// Not used for replies.
+    pub(crate) fn submit(self: DLArc<Self>) -> BinderResult {
+        // Defined before `process_inner` so that the destructor runs after releasing the lock.
+        let mut _t_outdated;
+
+        let oneway = self.flags & TF_ONE_WAY != 0;
+        let process = self.to.clone();
+        let mut process_inner = process.inner.lock();
+
+        self.set_outstanding(&mut process_inner);
+
+        if oneway {
+            if let Some(target_node) = self.target_node.clone() {
+                if process_inner.is_frozen {
+                    process_inner.async_recv = true;
+                    if self.flags & TF_UPDATE_TXN != 0 {
+                        if let Some(t_outdated) =
+                            target_node.take_outdated_transaction(&self, &mut process_inner)
+                        {
+                            // Save the transaction to be dropped after locks are released.
+                            _t_outdated = t_outdated;
+                        }
+                    }
+                }
+                match target_node.submit_oneway(self, &mut process_inner) {
+                    Ok(()) => {}
+                    Err((err, work)) => {
+                        drop(process_inner);
+                        // Drop work after releasing process lock.
+                        drop(work);
+                        return Err(err);
+                    }
+                }
+
+                if process_inner.is_frozen {
+                    return Err(BinderError::new_frozen_oneway());
+                } else {
+                    return Ok(());
+                }
+            } else {
+                pr_err!("Failed to submit oneway transaction to node.");
+            }
+        }
+
+        if process_inner.is_frozen {
+            process_inner.sync_recv = true;
+            return Err(BinderError::new_frozen());
+        }
+
+        let res = if let Some(thread) = self.find_target_thread() {
+            match thread.push_work(self) {
+                PushWorkRes::Ok => Ok(()),
+                PushWorkRes::FailedDead(me) => Err((BinderError::new_dead(), me)),
+            }
+        } else {
+            process_inner.push_work(self)
+        };
+        drop(process_inner);
+
+        match res {
+            Ok(()) => Ok(()),
+            Err((err, work)) => {
+                // Drop work after releasing process lock.
+                drop(work);
+                Err(err)
+            }
+        }
+    }
+
+    /// Check whether one oneway transaction can supersede another.
+    pub(crate) fn can_replace(&self, old: &Transaction) -> bool {
+        if self.from.process.task.pid() != old.from.process.task.pid() {
+            return false;
+        }
+
+        if self.flags & old.flags & (TF_ONE_WAY | TF_UPDATE_TXN) != (TF_ONE_WAY | TF_UPDATE_TXN) {
+            return false;
+        }
+
+        let target_node_match = match (self.target_node.as_ref(), old.target_node.as_ref()) {
+            (None, None) => true,
+            (Some(tn1), Some(tn2)) => Arc::ptr_eq(tn1, tn2),
+            _ => false,
+        };
+
+        self.code == old.code && self.flags == old.flags && target_node_match
+    }
+
+    fn prepare_file_list(&self) -> Result<TranslatedFds> {
+        let mut alloc = self.allocation.lock().take().ok_or(ESRCH)?;
+
+        match alloc.translate_fds() {
+            Ok(translated) => {
+                *self.allocation.lock() = Some(alloc);
+                Ok(translated)
+            }
+            Err(err) => {
+                // Free the allocation eagerly.
+                drop(alloc);
+                Err(err)
+            }
+        }
+    }
+}
+
+impl DeliverToRead for Transaction {
+    fn do_work(
+        self: DArc<Self>,
+        thread: &Thread,
+        writer: &mut BinderReturnWriter<'_>,
+    ) -> Result<bool> {
+        let send_failed_reply = ScopeGuard::new(|| {
+            if self.target_node.is_some() && self.flags & TF_ONE_WAY == 0 {
+                let reply = Err(BR_FAILED_REPLY);
+                self.from.deliver_reply(reply, &self);
+            }
+            self.drop_outstanding_txn();
+        });
+
+        let files = if let Ok(list) = self.prepare_file_list() {
+            list
+        } else {
+            // On failure to process the list, we send a reply back to the sender and ignore the
+            // transaction on the recipient.
+            return Ok(true);
+        };
+
+        let mut tr_sec = BinderTransactionDataSecctx::default();
+        let tr = tr_sec.tr_data();
+        if let Some(target_node) = &self.target_node {
+            let (ptr, cookie) = target_node.get_id();
+            tr.target.ptr = ptr as _;
+            tr.cookie = cookie as _;
+        };
+        tr.code = self.code;
+        tr.flags = self.flags;
+        tr.data_size = self.data_size as _;
+        tr.data.ptr.buffer = self.data_address as _;
+        tr.offsets_size = self.offsets_size as _;
+        if tr.offsets_size > 0 {
+            tr.data.ptr.offsets = (self.data_address + ptr_align(self.data_size).unwrap()) as _;
+        }
+        tr.sender_euid = self.sender_euid.into_uid_in_current_ns();
+        tr.sender_pid = 0;
+        if self.target_node.is_some() && self.flags & TF_ONE_WAY == 0 {
+            // Not a reply and not one-way.
+            tr.sender_pid = self.from.process.pid_in_current_ns();
+        }
+        let code = if self.target_node.is_none() {
+            BR_REPLY
+        } else if self.txn_security_ctx_off.is_some() {
+            BR_TRANSACTION_SEC_CTX
+        } else {
+            BR_TRANSACTION
+        };
+
+        // Write the transaction code and data to the user buffer.
+        writer.write_code(code)?;
+        if let Some(off) = self.txn_security_ctx_off {
+            tr_sec.secctx = (self.data_address + off) as u64;
+            writer.write_payload(&tr_sec)?;
+        } else {
+            writer.write_payload(&*tr)?;
+        }
+
+        let mut alloc = self.allocation.lock().take().ok_or(ESRCH)?;
+
+        // Dismiss the completion of transaction with a failure. No failure paths are allowed from
+        // here on out.
+        send_failed_reply.dismiss();
+
+        // Commit files, and set FDs in FDA to be closed on buffer free.
+        let close_on_free = files.commit();
+        alloc.set_info_close_on_free(close_on_free);
+
+        // It is now the user's responsibility to clear the allocation.
+        alloc.keep_alive();
+
+        self.drop_outstanding_txn();
+
+        // When this is not a reply and not a oneway transaction, update `current_transaction`. If
+        // it's a reply, `current_transaction` has already been updated appropriately.
+        if self.target_node.is_some() && tr_sec.transaction_data.flags & TF_ONE_WAY == 0 {
+            thread.set_current_transaction(self);
+        }
+
+        Ok(false)
+    }
+
+    fn cancel(self: DArc<Self>) {
+        let allocation = self.allocation.lock().take();
+        drop(allocation);
+
+        // If this is not a reply or oneway transaction, then send a dead reply.
+        if self.target_node.is_some() && self.flags & TF_ONE_WAY == 0 {
+            let reply = Err(BR_DEAD_REPLY);
+            self.from.deliver_reply(reply, &self);
+        }
+
+        self.drop_outstanding_txn();
+    }
+
+    fn should_sync_wakeup(&self) -> bool {
+        self.flags & TF_ONE_WAY == 0
+    }
+
+    fn debug_print(&self, m: &SeqFile, _prefix: &str, tprefix: &str) -> Result<()> {
+        self.debug_print_inner(m, tprefix);
+        Ok(())
+    }
+}
+
+#[pinned_drop]
+impl PinnedDrop for Transaction {
+    fn drop(self: Pin<&mut Self>) {
+        self.drop_outstanding_txn();
+    }
+}

include/uapi/linux/android/binder.h

@@ -38,7 +38,7 @@ enum {
 	BINDER_TYPE_PTR		= B_PACK_CHARS('p', 't', '*', B_TYPE_LARGE),
 };
 
-enum {
+enum flat_binder_object_flags {
 	FLAT_BINDER_FLAG_PRIORITY_MASK = 0xff,
 	FLAT_BINDER_FLAG_ACCEPTS_FDS = 0x100,
 

rust/bindings/bindings_helper.h

@@ -50,6 +50,7 @@
 #include <linux/dma-mapping.h>
 #include <linux/errname.h>
 #include <linux/ethtool.h>
+#include <linux/fdtable.h>
 #include <linux/file.h>
 #include <linux/firmware.h>
 #include <linux/fs.h>
@@ -71,6 +72,7 @@
 #include <linux/sched.h>
 #include <linux/security.h>
 #include <linux/slab.h>
+#include <linux/task_work.h>
 #include <linux/tracepoint.h>
 #include <linux/wait.h>
 #include <linux/workqueue.h>
@@ -99,3 +101,9 @@ const xa_mark_t RUST_CONST_HELPER_XA_PRESENT = XA_PRESENT;
 
 const gfp_t RUST_CONST_HELPER_XA_FLAGS_ALLOC = XA_FLAGS_ALLOC;
 const gfp_t RUST_CONST_HELPER_XA_FLAGS_ALLOC1 = XA_FLAGS_ALLOC1;
+
+#if IS_ENABLED(CONFIG_ANDROID_BINDER_IPC_RUST)
+#include "../../drivers/android/binder/rust_binder.h"
+#include "../../drivers/android/binder/rust_binder_events.h"
+#include "../../drivers/android/binder/page_range_helper.h"
+#endif

rust/helpers/binder.c

@@ -0,0 +1,26 @@
+// SPDX-License-Identifier: GPL-2.0
+
+/*
+ * Copyright (C) 2025 Google LLC.
+ */
+
+#include <linux/list_lru.h>
+#include <linux/task_work.h>
+
+unsigned long rust_helper_list_lru_count(struct list_lru *lru)
+{
+	return list_lru_count(lru);
+}
+
+unsigned long rust_helper_list_lru_walk(struct list_lru *lru,
+					list_lru_walk_cb isolate, void *cb_arg,
+					unsigned long nr_to_walk)
+{
+	return list_lru_walk(lru, isolate, cb_arg, nr_to_walk);
+}
+
+void rust_helper_init_task_work(struct callback_head *twork,
+				task_work_func_t func)
+{
+	init_task_work(twork, func);
+}

rust/helpers/helpers.c

@@ -8,6 +8,7 @@
  */
 
 #include "auxiliary.c"
+#include "binder.c"
 #include "blk.c"
 #include "bug.c"
 #include "build_assert.c"

rust/helpers/page.c

@@ -2,6 +2,7 @@
 
 #include <linux/gfp.h>
 #include <linux/highmem.h>
+#include <linux/mm.h>
 
 struct page *rust_helper_alloc_pages(gfp_t gfp_mask, unsigned int order)
 {
@@ -17,3 +18,10 @@ void rust_helper_kunmap_local(const void *addr)
 {
 	kunmap_local(addr);
 }
+
+#ifndef NODE_NOT_IN_PAGE_FLAGS
+int rust_helper_page_to_nid(const struct page *page)
+{
+	return page_to_nid(page);
+}
+#endif

rust/helpers/security.c

@@ -17,4 +17,28 @@ void rust_helper_security_release_secctx(struct lsm_context *cp)
 {
 	security_release_secctx(cp);
 }
+
+int rust_helper_security_binder_set_context_mgr(const struct cred *mgr)
+{
+	return security_binder_set_context_mgr(mgr);
+}
+
+int rust_helper_security_binder_transaction(const struct cred *from,
+					    const struct cred *to)
+{
+	return security_binder_transaction(from, to);
+}
+
+int rust_helper_security_binder_transfer_binder(const struct cred *from,
+						const struct cred *to)
+{
+	return security_binder_transfer_binder(from, to);
+}
+
+int rust_helper_security_binder_transfer_file(const struct cred *from,
+					      const struct cred *to,
+					      const struct file *file)
+{
+	return security_binder_transfer_file(from, to, file);
+}
 #endif

rust/kernel/cred.rs

@@ -54,6 +54,12 @@ pub unsafe fn from_ptr<'a>(ptr: *const bindings::cred) -> &'a Credential {
         unsafe { &*ptr.cast() }
     }
 
+    /// Returns a raw pointer to the inner credential.
+    #[inline]
+    pub fn as_ptr(&self) -> *const bindings::cred {
+        self.0.get()
+    }
+
     /// Get the id for this security context.
     #[inline]
     pub fn get_secid(&self) -> u32 {

rust/kernel/page.rs

@@ -85,6 +85,12 @@ pub fn as_ptr(&self) -> *mut bindings::page {
         self.page.as_ptr()
     }
 
+    /// Get the node id containing this page.
+    pub fn nid(&self) -> i32 {
+        // SAFETY: Always safe to call with a valid page.
+        unsafe { bindings::page_to_nid(self.as_ptr()) }
+    }
+
     /// Runs a piece of code with this page mapped to an address.
     ///
     /// The page is unmapped when this call returns.

rust/kernel/security.rs

@@ -8,9 +8,46 @@
 
 use crate::{
     bindings,
+    cred::Credential,
     error::{to_result, Result},
+    fs::File,
 };
 
+/// Calls the security modules to determine if the given task can become the manager of a binder
+/// context.
+#[inline]
+pub fn binder_set_context_mgr(mgr: &Credential) -> Result {
+    // SAFETY: `mrg.0` is valid because the shared reference guarantees a nonzero refcount.
+    to_result(unsafe { bindings::security_binder_set_context_mgr(mgr.as_ptr()) })
+}
+
+/// Calls the security modules to determine if binder transactions are allowed from task `from` to
+/// task `to`.
+#[inline]
+pub fn binder_transaction(from: &Credential, to: &Credential) -> Result {
+    // SAFETY: `from` and `to` are valid because the shared references guarantee nonzero refcounts.
+    to_result(unsafe { bindings::security_binder_transaction(from.as_ptr(), to.as_ptr()) })
+}
+
+/// Calls the security modules to determine if task `from` is allowed to send binder objects
+/// (owned by itself or other processes) to task `to` through a binder transaction.
+#[inline]
+pub fn binder_transfer_binder(from: &Credential, to: &Credential) -> Result {
+    // SAFETY: `from` and `to` are valid because the shared references guarantee nonzero refcounts.
+    to_result(unsafe { bindings::security_binder_transfer_binder(from.as_ptr(), to.as_ptr()) })
+}
+
+/// Calls the security modules to determine if task `from` is allowed to send the given file to
+/// task `to` (which would get its own file descriptor) through a binder transaction.
+#[inline]
+pub fn binder_transfer_file(from: &Credential, to: &Credential, file: &File) -> Result {
+    // SAFETY: `from`, `to` and `file` are valid because the shared references guarantee nonzero
+    // refcounts.
+    to_result(unsafe {
+        bindings::security_binder_transfer_file(from.as_ptr(), to.as_ptr(), file.as_ptr())
+    })
+}
+
 /// A security context string.
 ///
 /// # Invariants

rust/uapi/uapi_helper.h

@@ -9,6 +9,7 @@
 #include <uapi/asm-generic/ioctl.h>
 #include <uapi/drm/drm.h>
 #include <uapi/drm/nova_drm.h>
+#include <uapi/linux/android/binder.h>
 #include <uapi/linux/mdio.h>
 #include <uapi/linux/mii.h>
 #include <uapi/linux/ethtool.h>