linux-kernel - Re: [Security] [PATCH v3 0/4] x86: clear XD

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Date:	Tue, 9 Nov 2010 10:56:04 -0800
From:	Kees Cook <kees.cook@...onical.com>
To:	Alan Cox <alan@...rguk.ukuu.org.uk>
Cc:	x86@...nel.org, linux-kernel@...r.kernel.org
Subject: Re: [Security] [PATCH v3 0/4] x86: clear XD_DISABLED flag on Intel
 to regain NX

On Tue, Nov 09, 2010 at 06:31:42PM +0000, Alan Cox wrote:
> > In a review[1] of reported hardware being used by Ubuntu bug reporters,
> > almost 10% of systems had an incorrectly configured BIOS, leaving their
> > systems unable to use the NX features of their CPU.
> 
> Ouch

Yeah :(

> > This change will clear the MSR_IA32_MISC_ENABLE_XD_DISABLE bit so that NX
> > cannot be inappropriately controlled by the BIOS on Intel CPUs.  If, under
> > very strange hardware configurations, NX actually needs to be disabled,
> > "noexec=off" can be used to restore the prior behavior.
> 
> Have you done an audit of CPU errata to ensure that none of these cases
> are ones where the BIOS has disabled it to avoid an erratum. I'd hate to
> turn it on and find out the BIOS actually turned it off for good reason !

Where can I find those details?

-Kees

-- 
Kees Cook
Ubuntu Security Team
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