linux-kernel - Re: [PATCH v2] kasan: don't emit builtin calls when sanitization is off

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Message-ID: <9e61ea96-e10e-e200-e88d-51fc202c36c9@virtuozzo.com>
Date:   Tue, 23 Jan 2018 12:35:13 +0300
From:   Andrey Ryabinin <aryabinin@...tuozzo.com>
To:     Andrew Morton <akpm@...ux-foundation.org>,
        Andrey Konovalov <andreyknvl@...gle.com>
Cc:     Masahiro Yamada <yamada.masahiro@...ionext.com>,
        Michal Marek <michal.lkml@...kovi.net>,
        Alexander Potapenko <glider@...gle.com>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        linux-kbuild@...r.kernel.org, linux-kernel@...r.kernel.org,
        kasan-dev@...glegroups.com, Kostya Serebryany <kcc@...gle.com>,
        Evgeniy Stepanov <eugenis@...gle.com>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Stephen Hines <srhines@...gle.com>,
        Pirama Arumuga Nainar <pirama@...gle.com>,
        Manoj Gupta <manojgupta@...gle.com>,
        Greg Hackmann <ghackmann@...gle.com>,
        Arnd Bergmann <arnd@...db.de>
Subject: Re: [PATCH v2] kasan: don't emit builtin calls when sanitization is
 off



On 01/23/2018 05:20 AM, Andrew Morton wrote:
> On Fri, 19 Jan 2018 18:58:12 +0100 Andrey Konovalov <andreyknvl@...gle.com> wrote:
> 
>> With KASAN enabled the kernel has two different memset() functions, one
>> with KASAN checks (memset) and one without (__memset). KASAN uses some
>> macro tricks to use the proper version where required. For example memset()
>> calls in mm/slub.c are without KASAN checks, since they operate on poisoned
>> slab object metadata.
>>
>> The issue is that clang emits memset() calls even when there is no memset()
>> in the source code. They get linked with improper memset() implementation
>> and the kernel fails to boot due to a huge amount of KASAN reports during
>> early boot stages.
>>
>> The solution is to add -fno-builtin flag for files with KASAN_SANITIZE := n
>> marker.
> 
> This clashes somewhat with Arnd's asan-rework-kconfig-settings.patch. 
> Could you two please put heads together and decide what we want for a
> final result?
> 
> Meanwhile I'll "fix" the reject with
> 
> +ifdef CONFIG_KASAN_EXTRA
>  CFLAGS_KASAN += $(call cc-option, -fsanitize-address-use-after-scope)
> +endif
> 

Looks correct.