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

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Message-ID: <20131127175442.GA28088@gmail.com>
Date:	Wed, 27 Nov 2013 18:54:42 +0100
From:	Ingo Molnar <mingo@...nel.org>
To:	Kees Cook <keescook@...omium.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


* Kees Cook <keescook@...omium.org> wrote:

> 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?

Well, it's better than 9%, but still almost an order of magnitude 
higher than the cost is today, and a lot of distros have 
CONFIG_CC_STACKPROTECTOR=y.

So it would be nice to measure how much the instruction count goes up 
in some realistic system-bound test. How much does something like 
kernel/built-in.o increase, as per 'size' output?

Thanks,

	Ingo
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