linux-kernel - Re: [GIT PULL] x86/txt for v2.6.32

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Date:	Sat, 03 Oct 2009 13:44:22 -0700
From:	Roland Dreier <rdreier@...co.com>
To:	Henrique de Moraes Holschuh <hmh@....eng.br>
Cc:	Pavel Machek <pavel@....cz>, "Wang\, Shane" <shane.wang@...el.com>,
	Arjan van de Ven <arjan@...radead.org>,
	"H. Peter Anvin" <hpa@...or.com>,
	"Rafael J. Wysocki" <rjw@...k.pl>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Ingo Molnar <mingo@...e.hu>,
	Thomas Gleixner <tglx@...utronix.de>,
	"Cihula\, Joseph" <joseph.cihula@...el.com>
Subject: Re: [GIT PULL] x86/txt for v2.6.32


 > > > So I modify the RAM content so that BIOS does not think measured
 > > > environment existed before suspend?

 > And it is ridiculously easy to pull off, too:
 > http://www.engadget.com/2008/02/21/cold-boot-disk-encryption-attack-is-shockingly-effective/
 > 
 > Shows the attack being used to read sensitive keys, but you can use it also
 > to *modify* system running state (it will be more difficult, as you need to
 > remove and replace the RAM while on S3 instead of S5, but it should be
 > doable by someone who knows what he is doing).

I believe the whole point of this TXT / S3 handling is that the resume
from S3 will then be able to detect that the contents of RAM have been
modified while the system was asleep.

TXT simply produces a reasonably trustworthy measurement of system
state.  If you modify RAM while the system is asleep, then you will not
be able to produce a measurement showing an unmodified system state.

 - R.
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