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

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Message-ID: <20190410173318.GA9052@linux.intel.com>
Date:   Wed, 10 Apr 2019 20:38:18 +0300
From:   Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>
To:     Sasha Levin <sashal@...nel.org>
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 10, 2019 at 12:04:32PM -0400, Sasha Levin wrote:
> On Wed, Apr 10, 2019 at 02:29:27PM +0300, Jarkko Sakkinen wrote:
> > On Sat, Apr 06, 2019 at 11:30:47AM -0400, Sasha Levin wrote:
> > > 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.
> > 
> > Obviously not but what is the reason of not implementing CRB but instead
> > making yet another interface? I mean CRB supports SMC call.
> > 
> > For me this is taking steps back as to the early days when there was
> > proprietary intefaces to TPM before TCG came along and stardized.
> > 
> > I'm sure that the TPM implementation itself could be reworked to
> > inteface using CRB. It would also be good for ARM as a platform as now
> > this new made up interface causes unwanted divergence. I thought that
> > throwing ad hoc intefaces everywhere is something that ARM Linux
> > community tries to reduce, not increase.
> 
> I'm not sure what the original reasons were for not using the CRB
> interface. Note that the paper is from a few years ago, and
> implementations of this fTPM existed before the paper, so it's very
> possible that it just predates CRB.
> 
> Either way, there is existing hardware that runs this TPM and I'm trying
> to get it out of Microsoft's tree and get it upstream. There's not much
> I could do about existing hardware at this point.

OK, the 2nd paragraph kind of is enough reason to pull it. Thanks for
elaborating this. Just wanted to get a clearer picture where this sits
in the universe. I'll do detailed review as soon as I have time.

I don't need to have the hardware as long as *someone* could give
tested-by for this.

/Jarkko