From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-oi0-f44.google.com (mail-oi0-f44.google.com [209.85.218.44]) by kanga.kvack.org (Postfix) with ESMTP id 9FB8A6B0255 for ; Tue, 8 Sep 2015 06:06:29 -0400 (EDT) Received: by oixx17 with SMTP id x17so55798105oix.0 for ; Tue, 08 Sep 2015 03:06:29 -0700 (PDT) Received: from szxga01-in.huawei.com (szxga01-in.huawei.com. [58.251.152.64]) by mx.google.com with ESMTPS id w185si1935232oib.41.2015.09.08.03.06.27 for (version=TLSv1 cipher=RC4-SHA bits=128/128); Tue, 08 Sep 2015 03:06:29 -0700 (PDT) Message-ID: <55EEAF37.5050402@huawei.com> Date: Tue, 8 Sep 2015 17:49:43 +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> In-Reply-To: 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 17:36, 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. 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