linux-kernel - Re: [PATCH v2] kasan: Initialize tag to 0xff in __kasan

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Message-ID: <20190523014732.GA17640@archlinux-epyc>
Date:   Wed, 22 May 2019 18:47:32 -0700
From:   Nathan Chancellor <natechancellor@...il.com>
To:     Andrey Konovalov <andreyknvl@...gle.com>
Cc:     Andrey Ryabinin <aryabinin@...tuozzo.com>,
        Alexander Potapenko <glider@...gle.com>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        kasan-dev <kasan-dev@...glegroups.com>,
        Linux Memory Management List <linux-mm@...ck.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        clang-built-linux@...glegroups.com
Subject: Re: [PATCH v2] kasan: Initialize tag to 0xff in __kasan_kmalloc

On Thu, May 02, 2019 at 06:40:52PM +0200, Andrey Konovalov wrote:
> On Thu, May 2, 2019 at 6:31 PM Nathan Chancellor
> <natechancellor@...il.com> wrote:
> >
> > When building with -Wuninitialized and CONFIG_KASAN_SW_TAGS unset, Clang
> > warns:
> >
> > mm/kasan/common.c:484:40: warning: variable 'tag' is uninitialized when
> > used here [-Wuninitialized]
> >         kasan_unpoison_shadow(set_tag(object, tag), size);
> >                                               ^~~
> >
> > set_tag ignores tag in this configuration but clang doesn't realize it
> > at this point in its pipeline, as it points to arch_kasan_set_tag as
> > being the point where it is used, which will later be expanded to
> > (void *)(object) without a use of tag. Initialize tag to 0xff, as it
> > removes this warning and doesn't change the meaning of the code.
> >
> > Link: https://github.com/ClangBuiltLinux/linux/issues/465
> > Signed-off-by: Nathan Chancellor <natechancellor@...il.com>
> 
> Reviewed-by: Andrey Konovalov <andreyknvl@...gle.com>
> 
> Thanks!
> 

Thanks Andrey! Did anyone else have any other comments or can this be
picked up?

Cheers,
Nathan