Messages in this thread Patch in this message | | | Date | Tue, 8 Sep 2015 17:49:43 +0800 | From | Xishi Qiu <> | Subject | Re: [PATCH] kasan: fix last shadow judgement in memory_is_poisoned_16() |
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On 2015/9/8 17:36, Andrey Ryabinin wrote:
> 2015-09-08 4:42 GMT+03:00 Xishi Qiu <qiuxishi@huawei.com>: >> The shadow which correspond 16 bytes may span 2 or 3 bytes. If shadow >> only take 2 bytes, we can return in "if (likely(!last_byte)) ...", but >> it calculates wrong, so fix it. >> > > Please, be more specific. Describe what is wrong with the current code and why, > what's the effect of this bug and how you fixed it. > >
If the 16 bytes memory is aligned on 8, then the shadow takes only 2 bytes. So we check "shadow_first_bytes" is enough, and need not to call "memory_is_poisoned_1(addr + 15);". The code "if (likely(IS_ALIGNED(addr, 8)))" is wrong judgement.
e.g. addr=0, so last_byte = 15 & KASAN_SHADOW_MASK = 7, then the code will continue to call "return memory_is_poisoned_1(addr + 15);"
Thanks, Xishi Qiu
>> Signed-off-by: Xishi Qiu <qiuxishi@huawei.com> >> --- >> mm/kasan/kasan.c | 3 +-- >> 1 files changed, 1 insertions(+), 2 deletions(-) >> >> diff --git a/mm/kasan/kasan.c b/mm/kasan/kasan.c >> index 7b28e9c..8da2114 100644 >> --- a/mm/kasan/kasan.c >> +++ b/mm/kasan/kasan.c >> @@ -135,12 +135,11 @@ static __always_inline bool memory_is_poisoned_16(unsigned long addr) >> >> if (unlikely(*shadow_addr)) { >> u16 shadow_first_bytes = *(u16 *)shadow_addr; >> - s8 last_byte = (addr + 15) & KASAN_SHADOW_MASK; >> >> if (unlikely(shadow_first_bytes)) >> return true; >> >> - if (likely(!last_byte)) >> + if (likely(IS_ALIGNED(addr, 8))) >> return false; >> >> return memory_is_poisoned_1(addr + 15); >> -- >> 1.7.1 >> >> > > . >
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