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

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Message-ID: <OFF057DDEC.475AAF27-ON852574A4.004BC636-852574A4.004CC1A3@us.ibm.com>
Date:	Wed, 13 Aug 2008 09:58:22 -0400
From:	Kenneth Goldman <kgoldman@...ibm.com>
To:	Greg KH <greg@...ah.com>
Cc:	linux-kernel@...r.kernel.org, linux-security-module@...r.kernel.org
Subject: Re: [PATCH 1/4] integrity: TPM internel kernel interface

Greg KH <greg@...ah.com> 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:
> >
> > > 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?

As I said, I'm a TCG/TPM person, so I can't address "the module could just
be unloaded" or "hotplug pci driver".  I'll leave that issue to the
Linux driver experts.

I was using the common meaning of hotplug, removing and replacing a
hardware component while power is on.  By that common definition, the
TPM would not be a hotpluggable component.

(As an aside, the TPM is commonly connected to the LPC bus on
the planar, not the PCI bus.)

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