Re: [PATCH 2/2] ftpm: firmware TPM running in TEE

[Sasha Levin]

On Wed, Apr 03, 2019 at 09:27:28PM +0300, Jarkko Sakkinen wrote:
> On Wed, Apr 03, 2019 at 09:18:27PM +0300, Jarkko Sakkinen wrote:
> > On Tue, Apr 02, 2019 at 03:33:16PM -0400, Sasha Levin wrote:
> > > This patch adds support for a software-only implementation of a TPM
> > > running in TEE.
> > >
> > > There is extensive documentation of the design here:
> > > https://www.microsoft.com/en-us/research/publication/ftpm-software-implementation-tpm-chip/ .
> > >
> > > As well as reference code for the firmware available here:
> > > https://github.com/Microsoft/ms-tpm-20-ref/tree/master/Samples/ARM32-FirmwareTPM
> > >
> > > Signed-off-by: Thirupathaiah Annapureddy <thiruan@xxxxxxxxxxxxx>
> > > Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
> >
> > What is the context anyway? I mean tpm_crb already supports fTPM running
> > in TZ.
>
> Might take 2-3 weeks before I have time to go through ftpm1.pdf with
> full concentration. I did search through the PDF for CRB and found
> zero hits.

The fTPM as described in that paper and implemented in practice does not
use the CRB interface, thus we can't use tpm_crb to interface with the
firmware TPM.

> The commit message should absolutely better explain what is going on
> and preferably there should be some more broad documentation in
> Documentation/security/tpm.

The code itself is just a small shim between the firmware TPM and the
kernel's TPM interface. There's really not much else to expand on in the
commit log.

I'll add some background to Documentation/security/tpm.

> Now this is just a random code dump and nothing else.

It pretty much is, but that's because this is just a "stupid" shim,
there heavy lifting is done outside of the kernel.

> Also, I have zero idea how to test this. Any recommendations on ARM
> board that can be easily used to test custom TZ applications would be
> nice.

We are testing this on a Broadcom's Stingray SST100 board, and if you
have one we can help out with setting up a test environment. Otherwise,
we haven't really tried it on other boards.

--
Thanks,
Sasha