linux-kernel - Re: [tip:x86/asm] x86/i386: Make sure stack-protector segment base is cache aligned

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Date:	Thu, 3 Sep 2009 23:18:05 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	"H. Peter Anvin" <hpa@...or.com>
Cc:	Jeremy Fitzhardinge <jeremy@...p.org>, mingo@...hat.com,
	linux-kernel@...r.kernel.org, jeremy.fitzhardinge@...rix.com,
	stable@...nel.org, tglx@...utronix.de,
	linux-tip-commits@...r.kernel.org, Tejun Heo <tj@...nel.org>,
	Arjan van de Ven <arjan@...radead.org>
Subject: Re: [tip:x86/asm] x86/i386: Make sure stack-protector segment base
	is cache aligned


* H. Peter Anvin <hpa@...or.com> wrote:

> On 09/03/2009 01:45 PM, Jeremy Fitzhardinge wrote:
> > 
> > Two problems:
> > 
> >     * gcc generates %gs: references for stack-protector, but we use %fs
> >       for percpu data (because restoring %fs is faster if it's a null
> >       selector; TLS uses %gs).  I guess we could use %fs if
> >       !CONFIG_CC_STACKPROTECTOR, or %gs if we are using it (though that
> >       has some fiddly ramifications for things like ptrace).
> 
> Well, by touching two segments we're getting the worst of both 
> worlds, so at least assuming some significant number of real-world 
> deployments use CC_STACKPROTECTOR, we really don't want to 
> pessimize that case too much.

Fedora has stackprotector enabled so it's used in a widespread way.

	Ingo
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