linux-kernel - Re: [PATCH] kasan: fix last shadow judgement in memory_is_poisoned

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Date:	Tue, 8 Sep 2015 12:36:24 +0300
From:	Andrey Ryabinin <ryabinin.a.a@...il.com>
To:	Xishi Qiu <qiuxishi@...wei.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Andrey Konovalov <adech.fo@...il.com>,
	Rusty Russell <rusty@...tcorp.com.au>,
	Michal Marek <mmarek@...e.cz>, Linux MM <linux-mm@...ck.org>,
	LKML <linux-kernel@...r.kernel.org>, zhongjiang@...wei.com
Subject: Re: [PATCH] kasan: fix last shadow judgement in memory_is_poisoned_16()

2015-09-08 4:42 GMT+03:00 Xishi Qiu <qiuxishi@...wei.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.


> Signed-off-by: Xishi Qiu <qiuxishi@...wei.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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