From: Dennis Zhou <dennisszhou@gmail.com>
To: Fengguang Wu <fengguang.wu@intel.com>,
Ard Biesheuvel <ard.biesheuvel@linaro.org>,
Kees Cook <keescook@chromium.org>
Cc: linux-mm@kvack.org, Tejun Heo <tj@kernel.org>,
Christoph Lameter <cl@linux.com>,
Linus Torvalds <torvalds@linux-foundation.org>,
Josef Bacik <jbacik@fb.com>,
linux-kernel@vger.kernel.org, lkp@01.org,
Andrey Ryabinin <aryabinin@virtuozzo.com>,
Mark Rutland <mark.rutland@arm.com>
Subject: Re: [pcpu] BUG: KASAN: use-after-scope in pcpu_setup_first_chunk+0x1e3b/0x29e2
Date: Wed, 29 Nov 2017 11:54:30 -0600 [thread overview]
Message-ID: <20171129175430.GA58181@big-sky.attlocal.net> (raw)
In-Reply-To: <20171128124534.3jvuala525wvn64r@wfg-t540p.sh.intel.com>
Hi everyone,
I spent a bit of time learning more about this problem as Fengguang was
able to determine the root commit f7dd2507893cc3. I reproduced the bug
in userspace to make life a bit easier and below the assignment occurs
before the unpoison. This is fine if we're sequentially proceeding, but
as in the case in percpu, it's calling the function in a for loop
causing the assignment to happen after it has been poisoned in the prior
iteration.
<bb 3> [0.00%]:
_1 = (long unsigned int) i_4;
_2 = _1 * 16;
_3 = p_8 + _2;
list_14 = _3;
__u = {};
ASAN_MARK (UNPOISON, &__u, 8);
__u.__val = list_14;
<bb 9> [0.00%]:
_24 = __u.__val;
ASAN_MARK (POISON, &__u, 8);
list_14->prev = list_14;
i_13 = i_4 + 1;
<bb 10> [0.00%]:
# i_4 = PHI <i_9(2), i_13(9)>
if (i_4 <= 9)
goto <bb 3>; [0.00%]
else
goto <bb 11>; [0.00%]
I don't know how to go about fixing this though. The reproducing code is
below and was compiled with gcc-7 and the structleak_plugin.
I hope this helps.
Thanks,
Dennis
----
#include <stdint.h>
#include <stdlib.h>
#define barrier()
#define WRITE_ONCE(x, val) \
({ \
union { typeof(x) __val; char __c[1]; } __u = \
{ .__val = (typeof(x)) (val) }; \
__write_once_size(&(x), __u.__c, sizeof(x)); \
__u.__val; \
})
typedef uint8_t __u8;
typedef uint16_t __u16;
typedef uint32_t __u32;
typedef uint64_t __u64;
static inline __attribute__((always_inline)) void __write_once_size(volatile void *p, void *res, int size)
{
switch (size) {
case 1: *(volatile __u8 *)p = *(__u8 *)res; break;
case 2: *(volatile __u16 *)p = *(__u16 *)res; break;
case 4: *(volatile __u32 *)p = *(__u32 *)res; break;
case 8: *(volatile __u64 *)p = *(__u64 *)res; break;
default:
barrier();
__builtin_memcpy((void *)p, (const void *)res, size);
barrier();
}
}
struct list_head {
struct list_head *next, *prev;
};
static inline __attribute__((always_inline)) void INIT_LIST_HEAD(struct list_head *list)
{
WRITE_ONCE(list->next, list);
list->prev = list;
}
int main(int argc, char *argv[])
{
struct list_head *p = malloc(10 * sizeof(struct list_head));
int i;
for (i = 0; i < 10; i++) {
INIT_LIST_HEAD(&p[i]);
}
free(p);
return 0;
}
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next prev parent reply other threads:[~2017-11-29 17:54 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-11-26 6:31 [pcpu] BUG: KASAN: use-after-scope in pcpu_setup_first_chunk+0x1e3b/0x29e2 Fengguang Wu
2017-11-27 21:03 ` Dennis Zhou
2017-11-28 12:45 ` Fengguang Wu
2017-11-29 17:54 ` Dennis Zhou [this message]
2017-11-30 9:59 ` Dmitry Vyukov
2017-11-30 18:10 ` Kees Cook
2017-11-30 19:22 ` Dennis Zhou
2017-11-30 19:56 ` Kees Cook
2017-11-30 19:58 ` Ard Biesheuvel
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