linux-kernel - Re: [PATCH v2] use -fstack-protector-strong

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Date:	Wed, 27 Nov 2013 09:21:33 -0800
From:	Kees Cook <keescook@...omium.org>
To:	Ingo Molnar <mingo@...nel.org>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Nicolas Pitre <nicolas.pitre@...aro.org>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	Russell King <linux@....linux.org.uk>,
	Thomas Gleixner <tglx@...utronix.de>,
	"x86@...nel.org" <x86@...nel.org>,
	Shawn Guo <shawn.guo@...aro.org>,
	Olof Johansson <olofj@...omium.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH v2] use -fstack-protector-strong

On Wed, Nov 27, 2013 at 3:27 AM, Ingo Molnar <mingo@...nel.org> wrote:
>
> * Kees Cook <keescook@...omium.org> wrote:
>
>> On a defconfig x86_64 build (with CONFIG_CC_STACKPROTECTOR enabled), the
>> delta in size is just under 9% larger:
>>
>>  -rwxrwxr-x 1 kees kees  22134340 Nov 26 10:28 vmlinux.gcc-4.8
>>  -rwxrwxr-x 1 kees kees  22123870 Nov 26 10:40 vmlinux.gcc-4.9
>>  -rwxrwxr-x 1 kees kees  24225118 Nov 26 10:42 vmlinux.gcc-4.9+strong
>
> Please run it through 'size' so that we know the real text size
> increases.

   text    data     bss     dec     hex filename
11407474        1453792 1191936 14053202         d66f52 vmlinux.gcc-4.8
11458837        1457504 1191936 14108277         d74675 vmlinux.gcc-4.9
11682929        1457504 1191936 14332369         dab1d1 vmlinux.gcc-4.9+strong

Looks to be 2% for defconfig. That's way better. Shall I send a v3?

> If the cost of -fstack-protector-strong is really +9% in kernel text
> size then that's rather significant!
>
> If this option blows up our performance critical codepaths as well
> then this will likely cause a runtime slowdown as well, in addition to
> the increase in I$ footprint. That needs to be measured.
>
> CONFIG_CC_STACKPROTECTOR=y is relatively cheap today. For example on
> x86-64 defconfig:
>
>       text    data    bss     dec       filename
>   11378972    1455056 1191936 14025964  vmlinux  # CONFIG_CC_STACKPROTECTOR is not set
>   11420243    1455056 1191936 14067235  vmlinux  CONFIG_CC_STACKPROTECTOR=y
>
> that's a +0.3% cost currently.

Yeah -- not a lot of functions have char arrays. :)

>
> Thanks,
>
>         Ingo

-Kees

-- 
Kees Cook
Chrome OS Security
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