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, let KCSAN ignore all reads in the
region to silence KCSAN in case the write side is non-atomic.
Suggested-by: Marco Elver <[email protected]>
Signed-off-by: Qian Cai <[email protected]>
---
mm/kmemleak.c | 2 ++
1 file changed, 2 insertions(+)
diff --git a/mm/kmemleak.c b/mm/kmemleak.c
index e362dc3d2028..5e252d91eb14 100644
--- a/mm/kmemleak.c
+++ b/mm/kmemleak.c
@@ -1169,8 +1169,10 @@ static bool update_checksum(struct kmemleak_object *object)
u32 old_csum = object->checksum;
kasan_disable_current();
+ kcsan_disable_current();
object->checksum = crc32(0, (void *)object->pointer, object->size);
kasan_enable_current();
+ kcsan_enable_current();
return object->checksum != old_csum;
}
--
2.21.0 (Apple Git-122.2)
On Tue, 17 Mar 2020 at 19:28, Qian Cai <[email protected]> wrote:
>
> 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, let KCSAN ignore all reads in the
> region to silence KCSAN in case the write side is non-atomic.
>
> Suggested-by: Marco Elver <[email protected]>
> Signed-off-by: Qian Cai <[email protected]>
Acked-by: Marco Elver <[email protected]>
Thanks,
-- Marco
> ---
> mm/kmemleak.c | 2 ++
> 1 file changed, 2 insertions(+)
>
> diff --git a/mm/kmemleak.c b/mm/kmemleak.c
> index e362dc3d2028..5e252d91eb14 100644
> --- a/mm/kmemleak.c
> +++ b/mm/kmemleak.c
> @@ -1169,8 +1169,10 @@ static bool update_checksum(struct kmemleak_object *object)
> u32 old_csum = object->checksum;
>
> kasan_disable_current();
> + kcsan_disable_current();
> object->checksum = crc32(0, (void *)object->pointer, object->size);
> kasan_enable_current();
> + kcsan_enable_current();
>
> return object->checksum != old_csum;
> }
> --
> 2.21.0 (Apple Git-122.2)
>
On Tue, Mar 17, 2020 at 02:27:54PM -0400, Qian Cai wrote:
> 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, let KCSAN ignore all reads in the
> region to silence KCSAN in case the write side is non-atomic.
>
> Suggested-by: Marco Elver <[email protected]>
> Signed-off-by: Qian Cai <[email protected]>
Acked-by: Catalin Marinas <[email protected]>