linux-kernel - Re: [PATCH V2] kasan: use IS_ALIGNED in memory_is_poisoned

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Message-ID: <CAPAsAGxf_OQD502cW1nbXJ7WdRxyKqTx6+BJJpJoD-Z6WFCZMg@mail.gmail.com>
Date:	Mon, 14 Sep 2015 18:17:19 +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>,
	"long.wanglong" <long.wanglong@...wei.com>,
	Linux MM <linux-mm@...ck.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH V2] kasan: use IS_ALIGNED in memory_is_poisoned_8()

2015-09-14 5:09 GMT+03:00 Xishi Qiu <qiuxishi@...wei.com>:
> Use IS_ALIGNED() to determine whether the shadow span two bytes.
> It generates less code and more readable. Add some comments in
> shadow check functions.
>
> Please apply "kasan: fix last shadow judgement in memory_is_poisoned_16()"
> first.
>
> Signed-off-by: Xishi Qiu <qiuxishi@...wei.com>
> ---
>  mm/kasan/kasan.c | 21 +++++++++++++++++++--
>  1 file changed, 19 insertions(+), 2 deletions(-)
>
> diff --git a/mm/kasan/kasan.c b/mm/kasan/kasan.c
> index 8da2114..00d5605 100644
> --- a/mm/kasan/kasan.c
> +++ b/mm/kasan/kasan.c
> @@ -86,6 +86,10 @@ static __always_inline bool memory_is_poisoned_2(unsigned long addr)
>                 if (memory_is_poisoned_1(addr + 1))
>                         return true;
>
> +               /*
> +                * If the shadow spans two bytes, the first byte should
> +                * be zero.

Hmm.. I found this comment a bit odd.

How about this:
/*
 * If single shadow byte covers 2-byte access,
 * we don't need to do anything more.
 * Otherwise, test the first shadow byte.
 */

?
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