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 <[email protected]> >> --- >> 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. Thanks, Xishi Qiu > > Best Regards > Wang Long > > > > > > . > -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
