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

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Message-ID: <20101110002153.7af92a1f@lxorguk.ukuu.org.uk>
Date:	Wed, 10 Nov 2010 00:21:53 +0000
From:	Alan Cox <alan@...rguk.ukuu.org.uk>
To:	Kees Cook <kees.cook@...onical.com>
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

> Only Intel has this problem (it's the only CPU that defines this MSR), so
> that'll reduce it. But Google is of no help to me on this; where can I find
> these documents?

www.intel.com 8)


> > I'm not specifically aware of any but I do know for example that there
> > are other CPU BIOS disablable features that some systems disable in the
> > BIOS for good reason (an ancient example being the original Pentium
> > REP MOVS optimisation on some steppings)
> 
> By definition there should be fewer errata CPUs than those than need their
> BIOS ignored, so I still think this patch makes sense (especially since it
> can trivially be worked around with the noexec=off boot option).

We need to be sure because the last thing you want is even 1% of your 10%
of users to sudden get magical random memory corruption from overriding
something wrongly !

It's definitely worth checking and worth doing because even if there is
one (and I have no idea if there is) it'll tell you which steppings

Alan
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