2021-03-29 09:53:34

by Yang Li

Subject: [PATCH] x86/mce/dev-mcelog: Fix potential memory access error

Using set_bit() to set a bit in an integer is not a good idea, since
the function expects an unsigned long as argument, which can be 64bit
wide.
Coverity reports this problem as

High:Out-of-bounds access(INCOMPATIBLE_CAST)
CWE119: Out-of-bounds access to a scalar
Pointer "&mcelog->flags" points to an object whose effective type is
"unsigned int" (32 bits, unsigned) but is dereferenced as a wider
"unsigned long" (64 bits, unsigned). This may lead to memory corruption.

/home/heyuan.shy/git-repo/linux/arch/x86/kernel/cpu/mce/dev-mcelog.c:
dev_mce_log

Just use BIT instead.

Reported-by: Abaci Robot <[email protected]>
Signed-off-by: Yang Li <[email protected]>
---
arch/x86/kernel/cpu/mce/dev-mcelog.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/kernel/cpu/mce/dev-mcelog.c b/arch/x86/kernel/cpu/mce/dev-mcelog.c
index 100fbee..fd7b1b4 100644
--- a/arch/x86/kernel/cpu/mce/dev-mcelog.c
+++ b/arch/x86/kernel/cpu/mce/dev-mcelog.c
@@ -51,7 +51,7 @@ static int dev_mce_log(struct notifier_block *nb, unsigned long val,
* earlier errors are the more interesting ones:
*/
if (entry >= mcelog->len) {
- set_bit(MCE_OVERFLOW, (unsigned long *)&mcelog->flags);
+ mcelog->flags |= BIT(MCE_OVERFLOW);
goto unlock;
}

--
1.8.3.1

2021-03-29 16:14:41

by Luck, Tony

Subject: RE: [PATCH] x86/mce/dev-mcelog: Fix potential memory access error

- set_bit(MCE_OVERFLOW, (unsigned long *)&mcelog->flags);
+ mcelog->flags |= BIT(MCE_OVERFLOW);

set_bit() is an atomic operation because it might race with the code to
get and clear this bit:

do {
flags = mcelog->flags;
} while (cmpxchg(&mcelog->flags, flags, 0) != flags);

Originally this was needed because mcelog could be called from #MC
context.

That's all changed now and the machine check notifier chain routines are
called in a kernel thread. So some other locking (mutex?) could be used
to protect access to mcelog->flags.

-Tony