Re: [PATCH] kasan: use IS_ALIGNED in memory_is_poisoned_8()

Andrew Morton
2015-09-11T22:47:32Z

On Fri, 11 Sep 2015 10:02:29 +0800 Xishi Qiu <qiuxishi@huawei.com> wrote:

> Use IS_ALIGNED() to determine whether the shadow span two bytes.
> It generates less code and more readable.
>

Please cc Andrey Ryabinin on kasan patches.

> --- a/mm/kasan/kasan.c
> +++ b/mm/kasan/kasan.c
> @@ -120,7 +120,7 @@ static __always_inline bool memory_is_poisoned_8(unsigned long addr)
> if (memory_is_poisoned_1(addr + 7))
> return true;
>
> - if (likely(((addr + 7) & KASAN_SHADOW_MASK) >= 7))
> + if (likely(IS_ALIGNED(addr, 8)))
> return false;

Wouldn't IS_ALIGNED(addr, KASAN_SHADOW_SCALE_SIZE) be more appropriate?

But I'm not really sure what the original code is trying to do.

if ((addr + 7) & 7) >= 7)

can only evaluate true if ((addr + 7) & 7) equals 7, so the ">=" could
be "==".

I think. The code looks a bit weird. A code comment would help.

And how come memory_is_poisoned_16() does IS_ALIGNED(addr, 8)? Should
it be 16?