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compiler_types: Introduce __nocfi_generic 

There are two different ways that LLVM can expand kCFI operand bundles
in LLVM IR: generically in the middle end or using an architecture
specific sequence when lowering LLVM IR to machine code in the backend.
The generic pass allows any architecture to take advantage of kCFI but
the expansion of these bundles in the middle end can mess with
optimizations that may turn indirect calls into direct calls when the
call target is known at compile time, such as after inlining.

Add __nocfi_generic, dependent on an architecture selecting
CONFIG_ARCH_USES_CFI_GENERIC_LLVM_PASS, to disable kCFI bundle
generation in functions where only the generic kCFI pass may cause
problems.

Link: https://github.com/ClangBuiltLinux/linux/issues/2124
Signed-off-by: Nathan Chancellor <nathan@kernel.org>
Link: https://patch.msgid.link/20251025-idpf-fix-arm-kcfi-build-error-v1-1-ec57221153ae@kernel.org
Signed-off-by: Kees Cook <kees@kernel.org>
This commit is contained in:
Nathan Chancellor 2025-10-25 21:53:18 +01:00 committed by Kees Cook
parent 211ddde082
commit 39c89ee6e9
2 changed files with 13 additions and 0 deletions
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7
arch/Kconfig
View File

@ -917,6 +917,13 @@ config ARCH_USES_CFI_TRAPS
An architecture should select this option if it requires the
.kcfi_traps section for KCFI trap handling.
config ARCH_USES_CFI_GENERIC_LLVM_PASS
bool
help
An architecture should select this option if it uses the generic
KCFIPass in LLVM to expand kCFI bundles instead of architecture-specific
lowering.
config CFI
bool "Use Kernel Control Flow Integrity (kCFI)"
default CFI_CLANG

6
include/linux/compiler_types.h
View File

@ -461,6 +461,12 @@ struct ftrace_likely_data {
# define __nocfi
#endif
#if defined(CONFIG_ARCH_USES_CFI_GENERIC_LLVM_PASS)
# define __nocfi_generic __nocfi
#else
# define __nocfi_generic
#endif
/*
* Any place that could be marked with the "alloc_size" attribute is also
* a place to be marked with the "malloc" attribute, except those that may