linux-kernel - Re: [PATCH v2 5/5] Documentation: tpm: add documentation for the CRB FF-A interface

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Message-ID: <Z66ChI32MRi2q0xT@kernel.org>
Date: Fri, 14 Feb 2025 01:38:44 +0200
From: Jarkko Sakkinen <jarkko@...nel.org>
To: Stuart Yoder <stuart.yoder@....com>
Cc: linux-integrity@...r.kernel.org, peterhuewe@....de, jgg@...pe.ca,
	sudeep.holla@....com, rafael@...nel.org, lenb@...nel.org,
	linux-acpi@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 5/5] Documentation: tpm: add documentation for the CRB
 FF-A interface

On Thu, Feb 13, 2025 at 04:17:56PM -0600, Stuart Yoder wrote:
> 
> 
> On 2/13/25 4:11 PM, Jarkko Sakkinen wrote:
> > On Wed, Feb 12, 2025 at 04:05:48PM -0600, Stuart Yoder wrote:
> > > Add documentation providing details of how the CRB driver interacts
> > > with FF-A.
> > > 
> > > Signed-off-by: Stuart Yoder <stuart.yoder@....com>
> > > ---
> > >   Documentation/security/tpm/tpm_ffa_crb.rst | 65 ++++++++++++++++++++++
> > >   1 file changed, 65 insertions(+)
> > >   create mode 100644 Documentation/security/tpm/tpm_ffa_crb.rst
> > > 
> > > diff --git a/Documentation/security/tpm/tpm_ffa_crb.rst b/Documentation/security/tpm/tpm_ffa_crb.rst
> > > new file mode 100644
> > > index 000000000000..c70f8904a93d
> > > --- /dev/null
> > > +++ b/Documentation/security/tpm/tpm_ffa_crb.rst
> > > @@ -0,0 +1,65 @@
> > > +.. SPDX-License-Identifier: GPL-2.0
> > > +
> > > +========================
> > > +TPM CRB over FF-A Driver
> > > +========================
> > > +
> > > +The TPM Command Response Buffer (CRB) interface is a standard TPM interface
> > > +defined in the TCG PC Client Platform TPM Profile (PTP) Specification [1]_.
> > > +The CRB provides a structured set of control registers a client uses when
> > > +interacting with a TPM as well as a data buffer for storing TPM commands and
> > > +responses. A CRB interface can be implemented in:
> > > +
> > > +- hardware registers in a discrete TPM chip
> > > +
> > > +- in memory for a TPM running in isolated environment where shared memory
> > > +  allows a client to interact with the TPM
> > > +
> > > +The Firmware Framework for Arm A-profile (FF-A) [2]_ is a specification
> > > +that defines interfaces and protocols for the following purposes:
> > > +
> > > +- Compartmentalize firmware into software partitions that run in the Arm
> > > +  Secure world environment (also know as TrustZone)
> > 
> > Does that also cover ARM CCA? Just a question (not a review question).
> 
> No, CCA is for confidential VMs which is a separate trusted execution
> environment and FF-A is not used there.

OK, cool, just plain interested :-)

> 
> Thanks,
> Stuart

BR, Jarkko