linux-kernel - Re: [PATCH] arm64: lib: use C string functions with KASAN enabled.

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Message-ID: <9634affa-b210-d931-e40b-6e8a20f105fc@virtuozzo.com>
Date:   Fri, 7 Sep 2018 18:48:10 +0300
From:   Andrey Ryabinin <aryabinin@...tuozzo.com>
To:     Will Deacon <will.deacon@....com>
Cc:     Catalin Marinas <catalin.marinas@....com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Kyeongdon Kim <kyeongdon.kim@....com>,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        Alexander Potapenko <glider@...gle.com>,
        Dmitry Vyukov <dvyukov@...gle.com>, kasan-dev@...glegroups.com,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] arm64: lib: use C string functions with KASAN enabled.



On 09/07/2018 05:56 PM, Will Deacon wrote:
> On Thu, Sep 06, 2018 at 08:05:33PM +0300, Andrey Ryabinin wrote:
>> ARM64 has asm implementations of memchr(), memcmp(), str[r]chr(),
>> str[n]cmp(), str[n]len(). KASAN don't see memory accesses in asm
>> code, thus it can potentially miss many bugs.
>>
>> Ifdef out __HAVE_ARCH_* defines of these functions when KASAN is
>> enabled, so the generic implementations from lib/string.c will be used.
>>
>> Declare asm functions as weak instead of removing them because they
>> still can be used by efistub.
> 
> I don't understand this bit: efistub uses the __pi_ prefixed versions of the
> routines, so why do we need to declare them as weak?

Weak needed because we can't have two non-weak functions with the same name.

Alternative approach would be to never use e.g. "strlen" name for asm implementation of strlen() under CONFIG_KASAN=y.
But that would require adding some special ENDPIPROC_KASAN() macro since we want __pi_strlen() to point
to the asm_strlen().

Using weak seems like a way better solution to me.

> 
> Will
>