On 2015/9/8 17:49, Xishi Qiu wrote: > On 2015/9/8 17:36, Andrey Ryabinin wrote: > >> 2015-09-08 4:42 GMT+03:00 Xishi Qiu <qiuxi...@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.
Sorry, a mistake, The code "if (likely(!last_byte))" 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 <qiuxi...@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 >>> >>> >> >> . >> > > -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/