From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752787AbbIIIQO (ORCPT ); Wed, 9 Sep 2015 04:16:14 -0400 Received: from szxga02-in.huawei.com ([119.145.14.65]:65427 "EHLO szxga02-in.huawei.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751323AbbIIIQJ (ORCPT ); Wed, 9 Sep 2015 04:16:09 -0400 Message-ID: <55EFE959.4050105@huawei.com> Date: Wed, 9 Sep 2015 16:10:01 +0800 From: "long.wanglong" User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:16.0) Gecko/20121010 Thunderbird/16.0.1 MIME-Version: 1.0 To: Xishi Qiu CC: , Andrew Morton , Andrey Konovalov , Rusty Russell , Michal Marek , , Linux MM , LKML Subject: Re: [PATCH V2] kasan: fix last shadow judgement in memory_is_poisoned_16() References: <55EED09E.3010107@huawei.com> <55EFD46A.20309@huawei.com> <55EFE319.5000902@huawei.com> In-Reply-To: <55EFE319.5000902@huawei.com> Content-Type: text/plain; charset="ISO-8859-1" Content-Transfer-Encoding: 7bit X-Originating-IP: [10.111.152.157] X-CFilter-Loop: Reflected Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2015/9/9 15:43, Xishi Qiu wrote: > On 2015/9/9 14:40, long.wanglong wrote: > >> On 2015/9/8 20:12, Xishi Qiu wrote: >>> The shadow which correspond 16 bytes memory may span 2 or 3 bytes. If the >>> 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);". >>> But 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 "memory_is_poisoned_1(addr + 15);" >>> >>> 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); >>> >> >> Hi, >> I also notice this problem, how about another method to fix it: >> >> diff --git a/mm/kasan/kasan.c b/mm/kasan/kasan.c >> index 5d65d06..6a20dda 100644 >> --- a/mm/kasan/kasan.c >> +++ b/mm/kasan/kasan.c >> @@ -140,7 +140,7 @@ static __always_inline bool memory_is_poisoned_16(unsigned long addr) >> if (unlikely(shadow_first_bytes)) >> return true; >> >> - if (likely(!last_byte)) >> + if (likely(last_byte >= 7)) >> return false; >> >> return memory_is_poisoned_1(addr + 15); >> >> This method can ensure consistency of code, for example, in memory_is_poisoned_8: >> >> static __always_inline bool memory_is_poisoned_8(unsigned long addr) >> { >> u16 *shadow_addr = (u16 *)kasan_mem_to_shadow((void *)addr); >> >> if (unlikely(*shadow_addr)) { >> if (memory_is_poisoned_1(addr + 7)) >> return true; >> >> if (likely(((addr + 7) & KASAN_SHADOW_MASK) >= 7)) >> return false; >> >> return unlikely(*(u8 *)shadow_addr); >> } >> >> return false; >> } >> >> Otherwise, we also should use IS_ALIGNED macro in memory_is_poisoned_8! >> > > Hi Wanglong, > > How about use IS_ALIGNED instead of those code in memory_is_poisoned_8() > and other functions? I think the current code looks a bit ugly. > I think we can use IS_ALIGNED macro in memory_is_poisoned_8 and memory_is_poisoned_16. but for functions memory_is_poisoned_2 and memory_is_poisoned_4, we can't. Wang Long > Thanks, > Xishi Qiu > >> >> Best Regards >> Wang Long >> >> >> >> >> >> . >> > > > > > . >