linux-kernel - Re: [PATCH] kasan: Remove use after scope bugs detection.

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Message-ID: <20190116164712.GB1910@brain-police>
Date:   Wed, 16 Jan 2019 16:47:13 +0000
From:   Will Deacon <will.deacon@....com>
To:     Andrey Ryabinin <aryabinin@...tuozzo.com>
Cc:     akpm@...ux-foundation.org, linux-kernel@...r.kernel.org,
        kasan-dev@...glegroups.com, linux-mm@...ck.org,
        linux-arm-kernel@...ts.infradead.org, Qian Cai <cai@....pw>,
        Alexander Potapenko <glider@...gle.com>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Catalin Marinas <catalin.marinas@....com>
Subject: Re: [PATCH] kasan: Remove use after scope bugs detection.

On Fri, Jan 11, 2019 at 09:58:42PM +0300, Andrey Ryabinin wrote:
> Use after scope bugs detector seems to be almost entirely useless
> for the linux kernel. It exists over two years, but I've seen only
> one valid bug so far [1]. And the bug was fixed before it has been
> reported. There were some other use-after-scope reports, but they
> were false-positives due to different reasons like incompatibility
> with structleak plugin.
> 
> This feature significantly increases stack usage, especially with
> GCC < 9 version, and causes a 32K stack overflow. It probably
> adds performance penalty too.
> 
> Given all that, let's remove use-after-scope detector entirely.
> 
> While preparing this patch I've noticed that we mistakenly enable
> use-after-scope detection for clang compiler regardless of
> CONFIG_KASAN_EXTRA setting. This is also fixed now.
> 
> [1] http://lkml.kernel.org/r/<20171129052106.rhgbjhhis53hkgfn@...-t540p.sh.intel.com>
> 
> Signed-off-by: Andrey Ryabinin <aryabinin@...tuozzo.com>
> Cc: Qian Cai <cai@....pw>
> Cc: Alexander Potapenko <glider@...gle.com>
> Cc: Dmitry Vyukov <dvyukov@...gle.com>
> Cc: Catalin Marinas <catalin.marinas@....com>
> Cc: Will Deacon <will.deacon@....com>
> ---
>  arch/arm64/include/asm/memory.h |  4 ----
>  lib/Kconfig.debug               |  1 -
>  lib/Kconfig.kasan               | 10 ----------
>  lib/test_kasan.c                | 24 ------------------------
>  mm/kasan/generic.c              | 19 -------------------
>  mm/kasan/generic_report.c       |  3 ---
>  mm/kasan/kasan.h                |  3 ---
>  scripts/Makefile.kasan          |  5 -----
>  scripts/gcc-plugins/Kconfig     |  4 ----
>  9 files changed, 73 deletions(-)

For the arm64 part:

Acked-by: Will Deacon <will.deacon@....com>

but I defer to you and Dmitry as to whether or not you go ahead with this.

Will