linux-kernel - Re: [PATCH] x86/KASLR: use the right memcpy

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Date:   Tue, 30 May 2017 16:24:46 +0200
From:   Arnd Bergmann <arnd@...db.de>
To:     Baoquan He <bhe@...hat.com>
Cc:     Ingo Molnar <mingo@...hat.com>,
        "the arch/x86 maintainers" <x86@...nel.org>,
        "H. Peter Anvin" <hpa@...or.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Kees Cook <keescook@...omium.org>,
        Thomas Garnier <thgarnie@...gle.com>,
        Dave Jiang <dave.jiang@...el.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] x86/KASLR: use the right memcpy

On Tue, May 30, 2017 at 3:56 PM, Baoquan He <bhe@...hat.com> wrote:
> On 05/30/17 at 11:14am, Arnd Bergmann wrote:
>> The decompressor has its own implementation of the string functions,
>> but has to include the right header to get those, while implicitly
>> including linux/string.h may result in a link error:
>>
>> arch/x86/boot/compressed/kaslr.o: In function `choose_random_location':
>> kaslr.c:(.text+0xf51): undefined reference to `_mmx_memcpy'
>>
>> This has appeared now as kaslr started using memcpy. Other files in the
>> decompressor already do the same thing.
>>
>> Fixes: d52e7d5a952c ("x86/KASLR: Parse all 'memmap=' boot option entries")
>> Signed-off-by: Arnd Bergmann <arnd@...db.de>
>
> Thanks for this fix, Arnd!
>
> The linking error didn't happen when I tested the patch of d52e7d5a952c.
> Could you tell in what condition it will be triggered? Not sure if I
> should wait for this fix being merged and do a back porting, or can
> defer it if it's not risky.

It only happens on 32-bit kernels with CONFIG_X86_USE_3DNOW, maybe
there are additional requirements.

       Arnd