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

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Date:   Sat, 6 Apr 2019 11:30:47 -0400
From:   Sasha Levin <sashal@...nel.org>
To:     Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>
Cc:     robh+dt@...nel.org, mark.rutland@....com, peterhuewe@....de,
        jgg@...pe.ca, linux-kernel@...rosoft.com, bryankel@...rosoft.com,
        thiruan@...rosoft.com, suredd@...rosoft.com, arnd@...db.de,
        gregkh@...uxfoundation.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-integrity@...r.kernel.org
Subject: Re: [PATCH 2/2] ftpm: firmware TPM running in TEE

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@...rosoft.com>
>> > Signed-off-by: Sasha Levin <sashal@...nel.org>
>>
>> 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