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

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Message-ID: <20101109204857.GT5876@outflux.net>
Date:	Tue, 9 Nov 2010 12:48:57 -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

Hi Pekka,

On Tue, Nov 09, 2010 at 10:28:16PM +0200, Pekka Enberg wrote:
> So why can't we do patch 2/4 XD_DISABLE clearing in
> early_init_intel()?

Because it's too late, unfortunately. I went around a few times about this
with Peter Anvin, and ultimately he agreed that it needed to go in
verify_cpu() for now.

> Why do we want to call verify_cpu() from
> arch/x86/kernel/head_32.S and not from
> arch/x86/boot/compressed/head_32.S like we do on 64-bit?

Because the longmode/SSE tests being performed in verify_cpu() need to
happen that early for 64bit. Instead of including it in two places for
32bit, we can just include it once in arch/x86/kernel/head_32.S.

-Kees

-- 
Kees Cook
Ubuntu Security Team
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