mirror of https://github.com/torvalds/linux.git
a180bd1d7e
This warning was there to catch any architectures that still use
CONFIG_SET_FS, and that would mis-use iov_iter_init() for anything that
wasn't a proper user space pointer. So that
WARN_ON_ONCE(uaccess_kernel());
makes perfect conceptual sense: you really shouldn't use a kernel
pointer with set_fs(KERNEL_DS) and then pass it to iov_iter_init().
HOWEVER.
Guenter Roeck reports that this warning actually triggers in no-mmu
configurations of both ARM and m68k. And the reason isn't that they
pass in a kernel pointer under set_fs(KERNEL_DS) at all: the reason is
that in those configurations, "uaccess_kernel()" is simply not reliable.
Those no-mmu setups set USER_DS and KERNEL_DS to the same values, so you
can't test for the difference.
In particular, the no-mmu case for ARM does
#define USER_DS KERNEL_DS
#define uaccess_kernel() (true)
so USER_DS and KERNEL_DS have the same value, and uaccess_kernel() is
always trivially true.
The m68k case is slightly different and not quite as obvious. It does
(spread out over multiple header files just to be extra exciting:
asm/processor.h, asm/segment.h and asm-generic/uaccess.h):
#define TASK_SIZE (0xFFFFFFFFUL)
#define USER_DS MAKE_MM_SEG(TASK_SIZE)
#define KERNEL_DS MAKE_MM_SEG(~0UL)
#define get_fs() (current_thread_info()->addr_limit)
#define uaccess_kernel() (get_fs().seg == KERNEL_DS.seg)
but the end result is the same: uaccess_kernel() will always be true,
because USER_DS and KERNEL_DS end up having the same value, even if that
value is defined differently.
This is very arguably a misfeature in those implementations, but in the
end we don't really care. All modern architectures have gotten rid of
set_fs() already, and generic kernel code never uses it. And while the
sanity check was a nice idea, an architecture would have to go the extra
mile to actually break this.
So this well-intentioned warning isn't really all that likely to find
anything but these known false positives, and as such just isn't worth
maintaining.
Reported-by: Guenter Roeck <linux@roeck-us.net>
Fixes:
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|---|---|---|
| .. | ||
| 842 | ||
| crypto | ||
| dim | ||
| fonts | ||
| kunit | ||
| livepatch | ||
| lz4 | ||
| lzo | ||
| math | ||
| mpi | ||
| pldmfw | ||
| raid6 | ||
| reed_solomon | ||
| vdso | ||
| xz | ||
| zlib_deflate | ||
| zlib_dfltcc | ||
| zlib_inflate | ||
| zstd | ||
| .gitignore | ||
| Kconfig | ||
| Kconfig.debug | ||
| Kconfig.kasan | ||
| Kconfig.kcsan | ||
| Kconfig.kfence | ||
| Kconfig.kgdb | ||
| Kconfig.ubsan | ||
| Makefile | ||
| argv_split.c | ||
| ashldi3.c | ||
| ashrdi3.c | ||
| asn1_decoder.c | ||
| asn1_encoder.c | ||
| assoc_array.c | ||
| atomic64.c | ||
| atomic64_test.c | ||
| audit.c | ||
| bcd.c | ||
| bch.c | ||
| bitfield_kunit.c | ||
| bitmap.c | ||
| bitrev.c | ||
| bootconfig.c | ||
| bsearch.c | ||
| btree.c | ||
| bucket_locks.c | ||
| bug.c | ||
| build_OID_registry | ||
| buildid.c | ||
| bust_spinlocks.c | ||
| check_signature.c | ||
| checksum.c | ||
| clz_ctz.c | ||
| clz_tab.c | ||
| cmdline.c | ||
| cmdline_kunit.c | ||
| cmpdi2.c | ||
| compat_audit.c | ||
| cpu_rmap.c | ||
| cpumask.c | ||
| crc-ccitt.c | ||
| crc-itu-t.c | ||
| crc-t10dif.c | ||
| crc4.c | ||
| crc7.c | ||
| crc8.c | ||
| crc16.c | ||
| crc32.c | ||
| crc32defs.h | ||
| crc32test.c | ||
| crc64.c | ||
| ctype.c | ||
| debug_info.c | ||
| debug_locks.c | ||
| debugobjects.c | ||
| dec_and_lock.c | ||
| decompress.c | ||
| decompress_bunzip2.c | ||
| decompress_inflate.c | ||
| decompress_unlz4.c | ||
| decompress_unlzma.c | ||
| decompress_unlzo.c | ||
| decompress_unxz.c | ||
| decompress_unzstd.c | ||
| devmem_is_allowed.c | ||
| devres.c | ||
| digsig.c | ||
| dump_stack.c | ||
| dynamic_debug.c | ||
| dynamic_queue_limits.c | ||
| earlycpio.c | ||
| errname.c | ||
| error-inject.c | ||
| errseq.c | ||
| extable.c | ||
| fault-inject-usercopy.c | ||
| fault-inject.c | ||
| fdt.c | ||
| fdt_addresses.c | ||
| fdt_empty_tree.c | ||
| fdt_ro.c | ||
| fdt_rw.c | ||
| fdt_strerror.c | ||
| fdt_sw.c | ||
| fdt_wip.c | ||
| find_bit.c | ||
| find_bit_benchmark.c | ||
| flex_proportions.c | ||
| gen_crc32table.c | ||
| gen_crc64table.c | ||
| genalloc.c | ||
| generic-radix-tree.c | ||
| glob.c | ||
| globtest.c | ||
| hexdump.c | ||
| hweight.c | ||
| idr.c | ||
| inflate.c | ||
| interval_tree.c | ||
| interval_tree_test.c | ||
| iomap.c | ||
| iomap_copy.c | ||
| iommu-helper.c | ||
| iov_iter.c | ||
| irq_poll.c | ||
| irq_regs.c | ||
| is_single_threaded.c | ||
| kasprintf.c | ||
| kfifo.c | ||
| klist.c | ||
| kobject.c | ||
| kobject_uevent.c | ||
| kstrtox.c | ||
| kstrtox.h | ||
| libcrc32c.c | ||
| linear_ranges.c | ||
| list-test.c | ||
| list_debug.c | ||
| list_sort.c | ||
| llist.c | ||
| locking-selftest-hardirq.h | ||
| locking-selftest-mutex.h | ||
| locking-selftest-rlock-hardirq.h | ||
| locking-selftest-rlock-softirq.h | ||
| locking-selftest-rlock.h | ||
| locking-selftest-rsem.h | ||
| locking-selftest-rtmutex.h | ||
| locking-selftest-softirq.h | ||
| locking-selftest-spin-hardirq.h | ||
| locking-selftest-spin-softirq.h | ||
| locking-selftest-spin.h | ||
| locking-selftest-wlock-hardirq.h | ||
| locking-selftest-wlock-softirq.h | ||
| locking-selftest-wlock.h | ||
| locking-selftest-wsem.h | ||
| locking-selftest.c | ||
| lockref.c | ||
| logic_pio.c | ||
| lru_cache.c | ||
| lshrdi3.c | ||
| memcat_p.c | ||
| memory-notifier-error-inject.c | ||
| memregion.c | ||
| memweight.c | ||
| muldi3.c | ||
| net_utils.c | ||
| netdev-notifier-error-inject.c | ||
| nlattr.c | ||
| nmi_backtrace.c | ||
| nodemask.c | ||
| notifier-error-inject.c | ||
| notifier-error-inject.h | ||
| objagg.c | ||
| of-reconfig-notifier-error-inject.c | ||
| oid_registry.c | ||
| once.c | ||
| packing.c | ||
| parman.c | ||
| parser.c | ||
| pci_iomap.c | ||
| percpu-refcount.c | ||
| percpu_counter.c | ||
| percpu_test.c | ||
| plist.c | ||
| pm-notifier-error-inject.c | ||
| radix-tree.c | ||
| random32.c | ||
| ratelimit.c | ||
| rbtree.c | ||
| rbtree_test.c | ||
| refcount.c | ||
| rhashtable.c | ||
| sbitmap.c | ||
| scatterlist.c | ||
| seq_buf.c | ||
| sg_pool.c | ||
| sg_split.c | ||
| sha1.c | ||
| show_mem.c | ||
| siphash.c | ||
| slub_kunit.c | ||
| smp_processor_id.c | ||
| sort.c | ||
| stackdepot.c | ||
| stmp_device.c | ||
| string.c | ||
| string_helpers.c | ||
| strncpy_from_user.c | ||
| strnlen_user.c | ||
| syscall.c | ||
| test-kstrtox.c | ||
| test-string_helpers.c | ||
| test_bitmap.c | ||
| test_bitops.c | ||
| test_bits.c | ||
| test_blackhole_dev.c | ||
| test_bpf.c | ||
| test_debug_virtual.c | ||
| test_firmware.c | ||
| test_fpu.c | ||
| test_free_pages.c | ||
| test_hash.c | ||
| test_hexdump.c | ||
| test_hmm.c | ||
| test_hmm_uapi.h | ||
| test_ida.c | ||
| test_kasan.c | ||
| test_kasan_module.c | ||
| test_kmod.c | ||
| test_linear_ranges.c | ||
| test_list_sort.c | ||
| test_lockup.c | ||
| test_memcat_p.c | ||
| test_meminit.c | ||
| test_min_heap.c | ||
| test_module.c | ||
| test_objagg.c | ||
| test_overflow.c | ||
| test_parman.c | ||
| test_printf.c | ||
| test_rhashtable.c | ||
| test_scanf.c | ||
| test_siphash.c | ||
| test_sort.c | ||
| test_stackinit.c | ||
| test_static_key_base.c | ||
| test_static_keys.c | ||
| test_string.c | ||
| test_strscpy.c | ||
| test_sysctl.c | ||
| test_ubsan.c | ||
| test_user_copy.c | ||
| test_uuid.c | ||
| test_vmalloc.c | ||
| test_xarray.c | ||
| textsearch.c | ||
| timerqueue.c | ||
| ts_bm.c | ||
| ts_fsm.c | ||
| ts_kmp.c | ||
| ubsan.c | ||
| ubsan.h | ||
| ucmpdi2.c | ||
| ucs2_string.c | ||
| usercopy.c | ||
| uuid.c | ||
| vsprintf.c | ||
| win_minmax.c | ||
| xarray.c | ||
| xxhash.c | ||