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

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Message-ID: <20091017192800.GM16532@elf.ucw.cz>
Date:	Sat, 17 Oct 2009 21:28:00 +0200
From:	Pavel Machek <pavel@....cz>
To:	"Cihula, Joseph" <joseph.cihula@...el.com>
Cc:	Roland Dreier <rdreier@...co.com>,
	Henrique de Moraes Holschuh <hmh@....eng.br>,
	"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>
Subject: Re: [GIT PULL] x86/txt for v2.6.32

Hi!

> > >  > 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.
> >
> > ...and you are able to read out any keys, etc. Maybe that's expected &
> > ok, but Doc*/intel_txt.txt does not actually tell me what it protects
> > against and is pretty much useless... making patches impossible to
> > review.
> >
> > So... what does txt protect?
> 
> >From Documentation/intel_txt.txt:
>         Intel TXT in Brief:
>         o  Provides dynamic root of trust for measurement (DRTM)
>         o  Data protection in case of improper shutdown
>         o  Measurement and verification of launched environment
> 
> Intel TXT doesn't protect anything itself--it provides a foundation for software to provide protections and security.  tboot and the associated Linux patches do this.  The section of intel_txt.txt titled "Value Proposition for Linux or "Why should you care?"" tries to describe what is provided.
> 
> > Data integrity only?
> 
> Data integrity, yes, but not only.  The code also provides for DRTM-based measurements, data protection in case of improper shutdown, etc.
> 
> > Data privacy, too?
> 
> No.

So why does it protect data "in case of improper shutdown"?

> > Who is it designed to protect against?
> >
> > Remote attacker?
> 
> Yes.

Existing mechanisms should be adequate to protect against then.

> > Local user trying to subvert it?
> 
> No.

Then again, why does it protect data "in case of improper shutdown"?

> > > 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.
> >
> > Well, actually I see some auditing to be done in proposed patches.
> 
> All comments are welcome.

Well, without detailed design goals, comments are pretty much
impossible. Please improve Documentation/intel_txt.txt to explain what
it protects, and against who.
									Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
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