From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752536AbdJLHRC (ORCPT ); Thu, 12 Oct 2017 03:17:02 -0400 Received: from mail-io0-f182.google.com ([209.85.223.182]:50123 "EHLO mail-io0-f182.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751712AbdJLHRB (ORCPT ); Thu, 12 Oct 2017 03:17:01 -0400 X-Google-Smtp-Source: AOwi7QAdvtYY17CWzf8b7UpwP+0CIyfFD1+0Hw95SaQw9+xf3s8JKE5SNPbTQCHO8VFZn0zfGSRsH3mDYSCRKblyR0c= MIME-Version: 1.0 In-Reply-To: <20171011162345.f601c29d12c81af85bf38565@linux-foundation.org> References: <20171011082227.20546-1-liuwenliang@huawei.com> <20171011082227.20546-7-liuwenliang@huawei.com> <20171011162345.f601c29d12c81af85bf38565@linux-foundation.org> From: Dmitry Vyukov Date: Thu, 12 Oct 2017 09:16:39 +0200 Message-ID: Subject: Re: [PATCH 06/11] change memory_is_poisoned_16 for aligned error To: Andrew Morton Cc: Abbott Liu , Russell King - ARM Linux , Andrey Ryabinin , afzal.mohd.ma@gmail.com, f.fainelli@gmail.com, Laura Abbott , "Kirill A. Shutemov" , Michal Hocko , cdall@linaro.org, marc.zyngier@arm.com, Catalin Marinas , Matthew Wilcox , Thomas Gleixner , Thomas Garnier , Kees Cook , Arnd Bergmann , Vladimir Murzin , tixy@linaro.org, Ard Biesheuvel , robin.murphy@arm.com, Ingo Molnar , grygorii.strashko@linaro.org, Alexander Potapenko , opendmb@gmail.com, linux-arm-kernel@lists.infradead.org, LKML , kasan-dev , "linux-mm@kvack.org" , jiazhenghua@huawei.com, dylix.dailei@huawei.com, zengweilin@huawei.com, heshaoliang@huawei.com Content-Type: text/plain; charset="UTF-8" Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Oct 12, 2017 at 1:23 AM, Andrew Morton wrote: > On Wed, 11 Oct 2017 16:22:22 +0800 Abbott Liu wrote: > >> Because arm instruction set don't support access the address which is >> not aligned, so must change memory_is_poisoned_16 for arm. >> >> ... >> >> --- a/mm/kasan/kasan.c >> +++ b/mm/kasan/kasan.c >> @@ -149,6 +149,25 @@ static __always_inline bool memory_is_poisoned_2_4_8(unsigned long addr, >> return memory_is_poisoned_1(addr + size - 1); >> } >> >> +#ifdef CONFIG_ARM >> +static __always_inline bool memory_is_poisoned_16(unsigned long addr) >> +{ >> + u8 *shadow_addr = (u8 *)kasan_mem_to_shadow((void *)addr); >> + >> + if (unlikely(shadow_addr[0] || shadow_addr[1])) return true; > > Coding-style is messed up. Please use scripts/checkpatch.pl. > >> + else { >> + /* >> + * If two shadow bytes covers 16-byte access, we don't >> + * need to do anything more. Otherwise, test the last >> + * shadow byte. >> + */ >> + if (likely(IS_ALIGNED(addr, KASAN_SHADOW_SCALE_SIZE))) >> + return false; >> + return memory_is_poisoned_1(addr + 15); >> + } >> +} >> + >> +#else >> static __always_inline bool memory_is_poisoned_16(unsigned long addr) >> { >> u16 *shadow_addr = (u16 *)kasan_mem_to_shadow((void *)addr); >> @@ -159,6 +178,7 @@ static __always_inline bool memory_is_poisoned_16(unsigned long addr) >> >> return *shadow_addr; >> } >> +#endif > > - I don't understand why this is necessary. memory_is_poisoned_16() > already handles unaligned addresses? > > - If it's needed on ARM then presumably it will be needed on other > architectures, so CONFIG_ARM is insufficiently general. > > - If the present memory_is_poisoned_16() indeed doesn't work on ARM, > it would be better to generalize/fix it in some fashion rather than > creating a new variant of the function. Yes, I think it will be better to fix the current function rather then have 2 slightly different copies with ifdef's. Will something along these lines work for arm? 16-byte accesses are not too common, so it should not be a performance problem. And probably modern compilers can turn 2 1-byte checks into a 2-byte check where safe (x86). static __always_inline bool memory_is_poisoned_16(unsigned long addr) { u8 *shadow_addr = (u8 *)kasan_mem_to_shadow((void *)addr); if (shadow_addr[0] || shadow_addr[1]) return true; /* Unaligned 16-bytes access maps into 3 shadow bytes. */ if (unlikely(!IS_ALIGNED(addr, KASAN_SHADOW_SCALE_SIZE))) return memory_is_poisoned_1(addr + 15); return false; }