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

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Date:	Wed, 13 Aug 2008 12:56:40 -0400
From:	Mimi Zohar <zohar@...ibm.com>
To:	Greg KH <greg@...ah.com>
Cc:	Christoph Hellwig <hch@...radead.org>,
	Kenneth Goldman <kgoldman@...ibm.com>,
	linux-kernel@...r.kernel.org,
	linux-security-module@...r.kernel.org,
	linux-security-module-owner@...r.kernel.org
Subject: Re: [PATCH 1/4] integrity: TPM internel kernel interface

linux-security-module-owner@...r.kernel.org wrote on 08/12/2008 07:16:02 
PM:

> On Tue, Aug 12, 2008 at 04:57:31PM -0400, Kenneth Goldman wrote:
> > Christoph Hellwig <hch@...radead.org> wrote on 08/12/2008 03:30:31 PM:
> > 
> > > On Mon, Aug 11, 2008 at 05:13:51PM -0400, Mimi Zohar wrote:
> > > >
> > > > I assume the concern here is that between looking up the chip and
> > actually
> > > >
> > > > using the chip, the TPM chip is disabled/deactivated.  Based on
> > > > discussions
> > > > with Kenneth Goldman, the TCG main specification part2: 
structures,
> > > > require
> > > > that even if the TPM is disabled/deactivated, the command to 
extend the
> > 
> > > > PCR
> > > > will succeed, but the command to read the PCR will fail with an
> > > > appropriate
> > > > error code.
> > >
> > > And what happens when the chip simply goes away due to a hotplug 
action?
> > > Or not even the actual chip goes away but just the chip driver and 
you
> > > now dereference freed memory?
> > 
> > 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.
> 
> Load up the fake-php hotplug pci driver and "soft" disconnect it from
> the system :)
> 
> That was easy...
> 
> Note, just because you think your device is always going to be soldered
> to the motherboard, doesn't mean it can't be disconnected at any point
> in time with the kernel running.
>
> Or the module could just be unloaded, that's also a very common thing to
> have happen, right?

This problem only affects the TPM internal kernel interface, if the TPM 
driver is not built-in. For IMA, this is not an issue as the TPM driver 
must be built-in in order to start collecting measurements as soon as 
possible, which is at late_initcall().  I will resolve this problem for 
the general internal kernel interface usage case.

Thanks!

Mimi
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