On 2015/9/9 15:43, Xishi Qiu wrote: > On 2015/9/9 14:40, long.wanglong wrote: > >> On 2015/9/8 20:12, Xishi Qiu wrote: >>> The shadow which correspond 16 bytes memory may span 2 or 3 bytes. If the >>> 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);". >>> But 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 "memory_is_poisoned_1(addr + 15);" >>> >>> Signed-off-by: Xishi Qiu <qiuxishi@xxxxxxxxxx> >>> --- >>> 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); >>> >> >> Hi, >> I also notice this problem, how about another method to fix it: >> >> diff --git a/mm/kasan/kasan.c b/mm/kasan/kasan.c >> index 5d65d06..6a20dda 100644 >> --- a/mm/kasan/kasan.c >> +++ b/mm/kasan/kasan.c >> @@ -140,7 +140,7 @@ static __always_inline bool memory_is_poisoned_16(unsigned long addr) >> if (unlikely(shadow_first_bytes)) >> return true; >> >> - if (likely(!last_byte)) >> + if (likely(last_byte >= 7)) >> return false; >> >> return memory_is_poisoned_1(addr + 15); >> >> This method can ensure consistency of code, for example, in memory_is_poisoned_8: >> >> static __always_inline bool memory_is_poisoned_8(unsigned long addr) >> { >> u16 *shadow_addr = (u16 *)kasan_mem_to_shadow((void *)addr); >> >> if (unlikely(*shadow_addr)) { >> if (memory_is_poisoned_1(addr + 7)) >> return true; >> >> if (likely(((addr + 7) & KASAN_SHADOW_MASK) >= 7)) >> return false; >> >> return unlikely(*(u8 *)shadow_addr); >> } >> >> return false; >> } >> >> Otherwise, we also should use IS_ALIGNED macro in memory_is_poisoned_8! >> > > Hi Wanglong, > > How about use IS_ALIGNED instead of those code in memory_is_poisoned_8() > and other functions? I think the current code looks a bit ugly. > I think we can use IS_ALIGNED macro in memory_is_poisoned_8 and memory_is_poisoned_16. but for functions memory_is_poisoned_2 and memory_is_poisoned_4, we can't. Wang Long > Thanks, > Xishi Qiu > >> >> Best Regards >> Wang Long >> >> >> >> >> >> . >> > > > > > . > -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx"> email@xxxxxxxxx </a>