Re: Documenting the proposal for TPM 2.0 security in the face of bus interposer attacks

[Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>]

On Tue, Nov 20, 2018 at 09:25:43AM -0800, James Bottomley wrote:
> On Tue, 2018-11-20 at 14:41 +0200, Jarkko Sakkinen wrote:
> > On Tue, Nov 20, 2018 at 01:10:49PM +0200, Jarkko Sakkinen wrote:
> > > This is basically rewrite of TPM genie paper with extras. Maybe
> > > just shorten it to include the proposed architecture and point to
> > > the TPM Genie paper (which is not in the references at all ATM).
> > > 
> > > The way I see it the data validation is way more important than
> > > protecting against physical interposer to be frank.
> > > 
> > > The attack scenario would require to open the damn device. For
> > > laptop that would leave physical marks (i.e. evil maid). In a data
> > > center with armed guards I would wish you good luck accomplishing
> > > it. It is not anything like sticking a USB stick and run.
> > > 
> > > We can take a fix into Linux with a clean implementation but it
> > > needs to be an opt-in feature because not all users will want to
> > > use it.
> > 
> > Someone (might have been either Mimi or David Howells but cannot
> > recall) correctly pointed out at LSS 2018 that you could just as
> > easily spy and corrupt RAM if you have a time window to perform this
> > type of attack.
> 
> Not using the simple plug in on the TPM bus, you can't.  The point is
> basically the difference in the technology: the interposer is a simple,
> easy to construct, plugin; a RAM spy is a huge JTAG thing that would be
> hard even to fit into a modern thin laptop, let alone extremely
> difficult to build.

Why you wouldn't use DMA to spy the RAM?

/Jarkko