From: Daniel Borkmann <daniel@iogearbox.net>
To: bpf@vger.kernel.org
Cc: Daniel Borkmann <daniel@iogearbox.net>,
syzbot+97522333291430dd277f@syzkaller.appspotmail.com,
Marco Elver <elver@google.com>,
Yonghong Song <yonghong.song@linux.dev>
Subject: [PATCH bpf] bpf: Annotate bpf_long_memcpy with data_race
Date: Tue, 29 Aug 2023 22:53:52 +0200 [thread overview]
Message-ID: <57628f7a15e20d502247c3b55fceb1cb2b31f266.1693342186.git.daniel@iogearbox.net> (raw)
syzbot reported a data race splat between two processes trying to
update the same BPF map value via syscall on different CPUs:
BUG: KCSAN: data-race in bpf_percpu_array_update / bpf_percpu_array_update
write to 0xffffe8fffe7425d8 of 8 bytes by task 8257 on cpu 1:
bpf_long_memcpy include/linux/bpf.h:428 [inline]
bpf_obj_memcpy include/linux/bpf.h:441 [inline]
copy_map_value_long include/linux/bpf.h:464 [inline]
bpf_percpu_array_update+0x3bb/0x500 kernel/bpf/arraymap.c:380
bpf_map_update_value+0x190/0x370 kernel/bpf/syscall.c:175
generic_map_update_batch+0x3ae/0x4f0 kernel/bpf/syscall.c:1749
bpf_map_do_batch+0x2df/0x3d0 kernel/bpf/syscall.c:4648
__sys_bpf+0x28a/0x780
__do_sys_bpf kernel/bpf/syscall.c:5241 [inline]
__se_sys_bpf kernel/bpf/syscall.c:5239 [inline]
__x64_sys_bpf+0x43/0x50 kernel/bpf/syscall.c:5239
do_syscall_x64 arch/x86/entry/common.c:50 [inline]
do_syscall_64+0x41/0xc0 arch/x86/entry/common.c:80
entry_SYSCALL_64_after_hwframe+0x63/0xcd
write to 0xffffe8fffe7425d8 of 8 bytes by task 8268 on cpu 0:
bpf_long_memcpy include/linux/bpf.h:428 [inline]
bpf_obj_memcpy include/linux/bpf.h:441 [inline]
copy_map_value_long include/linux/bpf.h:464 [inline]
bpf_percpu_array_update+0x3bb/0x500 kernel/bpf/arraymap.c:380
bpf_map_update_value+0x190/0x370 kernel/bpf/syscall.c:175
generic_map_update_batch+0x3ae/0x4f0 kernel/bpf/syscall.c:1749
bpf_map_do_batch+0x2df/0x3d0 kernel/bpf/syscall.c:4648
__sys_bpf+0x28a/0x780
__do_sys_bpf kernel/bpf/syscall.c:5241 [inline]
__se_sys_bpf kernel/bpf/syscall.c:5239 [inline]
__x64_sys_bpf+0x43/0x50 kernel/bpf/syscall.c:5239
do_syscall_x64 arch/x86/entry/common.c:50 [inline]
do_syscall_64+0x41/0xc0 arch/x86/entry/common.c:80
entry_SYSCALL_64_after_hwframe+0x63/0xcd
value changed: 0x0000000000000000 -> 0xfffffff000002788
The bpf_long_memcpy is used with 8-byte aligned pointers, power-of-8 size
and forced to use long read/writes to try to atomically copy long counters.
It is best-effort only and no barriers are here since it _will_ race with
concurrent updates from BPF programs. The bpf_long_memcpy() is called from
bpf(2) syscall. Marco suggested that the best way to make this known to
KCSAN would be to use data_race() annotation.
Reported-by: syzbot+97522333291430dd277f@syzkaller.appspotmail.com
Suggested-by: Marco Elver <elver@google.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Cc: Yonghong Song <yonghong.song@linux.dev>
Link: https://lore.kernel.org/bpf/000000000000d87a7f06040c970c@google.com
---
include/linux/bpf.h | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/include/linux/bpf.h b/include/linux/bpf.h
index f58895830ada..eb1bb76e87f8 100644
--- a/include/linux/bpf.h
+++ b/include/linux/bpf.h
@@ -425,7 +425,7 @@ static inline void bpf_long_memcpy(void *dst, const void *src, u32 size)
size /= sizeof(long);
while (size--)
- *ldst++ = *lsrc++;
+ data_race(*ldst++ = *lsrc++);
}
/* copy everything but bpf_spin_lock, bpf_timer, and kptrs. There could be one of each. */
--
2.21.0
next reply other threads:[~2023-08-29 20:53 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-08-29 20:53 Daniel Borkmann [this message]
2023-08-29 21:07 ` [PATCH bpf] bpf: Annotate bpf_long_memcpy with data_race Marco Elver
2023-08-31 20:35 ` Daniel Borkmann
2023-08-31 20:30 ` patchwork-bot+netdevbpf
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