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

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Message-ID: <20090904071524.0a7267ce@infradead.org>
Date:	Fri, 4 Sep 2009 07:15:24 -0700
From:	Arjan van de Ven <arjan@...radead.org>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	"H. Peter Anvin" <hpa@...or.com>,
	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>
Subject: Re: [tip:x86/asm] x86/i386: Make sure stack-protector segment base
 is cache aligned

On Thu, 3 Sep 2009 23:18:05 +0200
Ingo Molnar <mingo@...e.hu> wrote:

> 
> * 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

the other issue is that afaik we want the kernel to use the other
register than userspace does...


-- 
Arjan van de Ven 	Intel Open Source Technology Centre
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