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

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Date:	Thu, 03 Sep 2009 14:21:19 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Ingo Molnar <mingo@...e.hu>
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

On 09/03/2009 02:18 PM, Ingo Molnar 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

I'm guessing most distros do, except perhaps embedded ones.

	-hpa
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