linux-kernel - Re: [PATCH 3/4] x86: call verify

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Message-ID: <20101109191908.GO5876@outflux.net>
Date:	Tue, 9 Nov 2010 11:19:08 -0800
From:	Kees Cook <kees.cook@...onical.com>
To:	Pekka Enberg <penberg@...nel.org>
Cc:	x86@...nel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 3/4] x86: call verify_cpu during 32bit CPU startup

On Tue, Nov 09, 2010 at 09:09:18PM +0200, Pekka Enberg wrote:
> On Tue, Nov 9, 2010 at 8:15 PM, Kees Cook <kees.cook@...onical.com> wrote:
> > The XD_DISABLE-clearing side-effect needs to happen on 32bit CPU
> > start-up as well.
> >
> > Signed-off-by: Kees Cook <kees.cook@...onical.com>
> 
> The patch description here is pretty damn terse. Why do we need the
> clearing for? Does not clearing XD_DISABLE cause some problem?

The clearing needs to happen for both 32bit and 64bit, but the 32bit init
routines were not calling verify_cpu() yet. This adds that path to gain the
side-effect. (See patch 0 for why clearing XD_DISABLE is important.)

-- 
Kees Cook
Ubuntu Security Team
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