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Date:	Sun, 3 Jul 2011 12:15:22 -0700
From:	Kees Cook <>
To:	Pavel Machek <>
Cc:, Len Brown <>,
	"Rafael J. Wysocki" <>,
	Thomas Gleixner <>,
	Ingo Molnar <>,
	"H. Peter Anvin" <>,,
	Pekka Enberg <>,
	Brian Gerst <>,
	Alan Cox <>
Subject: Re: [PATCH] x86: add missing verify_cpu to 32bit wakeup

Hi Pavel,

On Sun, Jul 03, 2011 at 02:15:49PM +0200, Pavel Machek wrote:
> > Some BIOSes will reset the Intel XD_DISABLE MSR bit when resuming from S3,
> > which can interact poorly with ebba638ae723d8a8fc2f7abce5ec18b688b791d7.
> > In 32bit PAE mode, this can lead to a fault when EFER is restored by
> > the kernel wakeup routines, due to it setting the NX bit for a CPU
> > that (thanks to the BIOS reset) now incorrectly thinks it lacks the NX
> > feature. 64bit wakeup already handled this through its common call path
> > that would hit verify_cpu(). 32bit has a separate path for restoring
> > CPU state on S3 wakeup, and needed to call verify_cpu() to handle this
> > situation.
> > 
> > Signed-off-by: Kees Cook <>
> > Cc:
> Looks ok to me, but I'm not sure it is stable material.

Well, I figured anything that shipped with
ebba638ae723d8a8fc2f7abce5ec18b688b791d7 should get it, since it is
a regression in the 32bit PAE with BIOS-disabled NX corner-case.


Kees Cook
Ubuntu Security Team
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