Even if KCSAN is disabled for kmemleak, update_checksum() could still call crc32() (which is outside of kmemleak.c) to dereference object->pointer. Thus, the value of object->pointer could be accessed concurrently as noticed by KCSAN, BUG: KCSAN: data-race in crc32_le_base / do_raw_spin_lock write to 0xffffb0ea683a7d50 of 4 bytes by task 23575 on cpu 12: do_raw_spin_lock+0x114/0x200 debug_spin_lock_after at kernel/locking/spinlock_debug.c:91 (inlined by) do_raw_spin_lock at kernel/locking/spinlock_debug.c:115 _raw_spin_lock+0x40/0x50 __handle_mm_fault+0xa9e/0xd00 handle_mm_fault+0xfc/0x2f0 do_page_fault+0x263/0x6f9 page_fault+0x34/0x40 read to 0xffffb0ea683a7d50 of 4 bytes by task 839 on cpu 60: crc32_le_base+0x67/0x350 crc32_le_base+0x67/0x350: crc32_body at lib/crc32.c:106 (inlined by) crc32_le_generic at lib/crc32.c:179 (inlined by) crc32_le at lib/crc32.c:197 kmemleak_scan+0x528/0xd90 update_checksum at mm/kmemleak.c:1172 (inlined by) kmemleak_scan at mm/kmemleak.c:1497 kmemleak_scan_thread+0xcc/0xfa kthread+0x1e0/0x200 ret_from_fork+0x27/0x50 If a shattered value was returned due to a data race, it will be corrected in the next scan. Thus, annotate it as an intentional data race using the data_race() macro. Signed-off-by: Qian Cai <cai@xxxxxx> --- mm/kmemleak.c | 7 ++++++- 1 file changed, 6 insertions(+), 1 deletion(-) diff --git a/mm/kmemleak.c b/mm/kmemleak.c index e362dc3d2028..d3327756c3a4 100644 --- a/mm/kmemleak.c +++ b/mm/kmemleak.c @@ -1169,7 +1169,12 @@ static bool update_checksum(struct kmemleak_object *object) u32 old_csum = object->checksum; kasan_disable_current(); - object->checksum = crc32(0, (void *)object->pointer, object->size); + /* + * crc32() will dereference object->pointer. If an unstable value was + * returned due to a data race, it will be corrected in the next scan. + */ + object->checksum = data_race(crc32(0, (void *)object->pointer, + object->size)); kasan_enable_current(); return object->checksum != old_csum; -- 2.21.0 (Apple Git-122.2)
