From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-io0-f174.google.com (mail-io0-f174.google.com [209.85.223.174]) by kanga.kvack.org (Postfix) with ESMTP id E9F476B0038 for ; Tue, 8 Sep 2015 05:56:56 -0400 (EDT) Received: by iofh134 with SMTP id h134so111824263iof.0 for ; Tue, 08 Sep 2015 02:56:56 -0700 (PDT) Received: from szxga01-in.huawei.com (szxga01-in.huawei.com. [58.251.152.64]) by mx.google.com with ESMTPS id 17si4620982pdg.139.2015.09.08.02.56.55 for (version=TLS1 cipher=RC4-SHA bits=128/128); Tue, 08 Sep 2015 02:56:56 -0700 (PDT) Message-ID: <55EEAFD7.8010409@huawei.com> Date: Tue, 8 Sep 2015 17:52:23 +0800 From: Xishi Qiu MIME-Version: 1.0 Subject: Re: [PATCH] kasan: fix last shadow judgement in memory_is_poisoned_16() References: <55EE3D03.8000502@huawei.com> <55EEAF37.5050402@huawei.com> In-Reply-To: <55EEAF37.5050402@huawei.com> Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Andrey Ryabinin Cc: Andrew Morton , Andrey Konovalov , Rusty Russell , Michal Marek , Linux MM , LKML , zhongjiang@huawei.com On 2015/9/8 17:49, Xishi Qiu wrote: > On 2015/9/8 17:36, Andrey Ryabinin wrote: > >> 2015-09-08 4:42 GMT+03:00 Xishi Qiu : >>> 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. >> >> > > If the 16 bytes 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);". > The code "if (likely(IS_ALIGNED(addr, 8)))" is wrong judgement. Sorry, a mistake, 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 "return memory_is_poisoned_1(addr + 15);" > > Thanks, > Xishi Qiu > >>> Signed-off-by: Xishi Qiu >>> --- >>> 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 >>> >>> >> >> . >> > > -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org