2020-02-11 18:48:40

by Qian Cai

Subject: [PATCH -next] mm/kmemleak: annotate a data race in checksum

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

Reported by Kernel Concurrency Sanitizer on:
CPU: 60 PID: 839 Comm: kmemleak Tainted: G W L 5.5.0-next-20200210+ #3
Hardware name: HPE ProLiant DL385 Gen10/ProLiant DL385 Gen10, BIOS A40 07/10/2019

crc32() will dereference object->pointer. 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 <[email protected]>
---
mm/kmemleak.c | 7 ++++++-
1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/mm/kmemleak.c b/mm/kmemleak.c
index 3a4259eeb5a0..25b4bcc32b5f 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;
--
1.8.3.1

2020-02-11 19:28:14

by Catalin Marinas

Subject: Re: [PATCH -next] mm/kmemleak: annotate a data race in checksum

On Tue, Feb 11, 2020 at 11:24:05AM -0500, Qian Cai wrote:
> 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
>
> Reported by Kernel Concurrency Sanitizer on:
> CPU: 60 PID: 839 Comm: kmemleak Tainted: G W L 5.5.0-next-20200210+ #3
> Hardware name: HPE ProLiant DL385 Gen10/ProLiant DL385 Gen10, BIOS A40 07/10/2019
>
> crc32() will dereference object->pointer. 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 <[email protected]>

Acked-by: Catalin Marinas <[email protected]>