linux-kernel - Re: [PATCH 1/4] integrity: TPM internel kernel interface

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Message-ID: <OFC8FDDFED.7F31F3B8-ON852574A4.004A3882-852574A4.004BA8FA@us.ibm.com>
Date:	Wed, 13 Aug 2008 09:46:24 -0400
From:	Kenneth Goldman <kgoldman@...ibm.com>
To:	Alan Cox <alan@...rguk.ukuu.org.uk>
Cc:	linux-kernel@...r.kernel.org, linux-security-module@...r.kernel.org
Subject: Re: [PATCH 1/4] integrity: TPM internel kernel interface

Alan Cox <alan@...rguk.ukuu.org.uk> wrote on 08/12/2008 05:36:36 PM:

> > Being a TCG/TPM person, I can only address the first question.  The
> > intent is that the TPM is soldered to the planar/motherboard (the TCG
> > uses the phrase "bound to the platform").  I can't imagine
> > any manufacturer designing a pluggable TPM.  It would subvert PCR
> > measurements and thus attestation, data sealing, etc.
>
> So the security limit of your TPM is a soldering iron .. whoo. I'm not
> sure this is actually the case however as the secret of interest is in
> the TPM so even if I replaced the TPM the goodies already set up are in
> the TPM I just unsoldered surely ?

I suppose it depends on the precise interpretation of your technical
term "goodies".  :-)

One of the two primary uses of the TCG technology is protection
against an attack on the software.  The TCG uses the terms
attestation, integrity, platform measurements, etc.  For this class of>
"goodies", the TCG technology does not protect against hardware
attacks such as replacing the TPM with a bogus device, replacing the
CRTM hardware, flashing the CRTM using a JTAG cable, lifting a TPM pin>
and asserting reset, using a JTAG cable to set breakpoints and alter
memory, etc.

For this use case, the attack model is a remote, software attack.  The>
user is not considered the attacker.

(In the other primary use case, the user is the attacker, but it's an
entirely different discussion.)

(It's also important to note that the TPM itself does not completely
secure the platform.  There's an entire system design around it, which>
it why I try to say "TCG technology" rather than TPM.)

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