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    SubjectRE: [GIT PULL] x86/txt for v2.6.32
    > From: Pavel Machek [mailto:pavel@ucw.cz]
    > Sent: Tuesday, October 06, 2009 1:13 AM
    >
    > On Sat 2009-10-03 13:44:22, Roland Dreier wrote:
    > >
    > > > > > 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.
    >
    > ...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.

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

    Yes.

    > Local user trying to subvert it?

    No.

    > ...and has soldering iron he's willing to use?
    >
    > ...and has soldering iron, osciloscope and PCI analyzer he's willing to use?

    No and no.

    > > 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.

    Joe


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