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

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Message-ID: <b9a7d98a-2723-45e0-bb3b-19cd31473251@arm.com>
Date: Thu, 13 Feb 2025 16:17:56 -0600
From: Stuart Yoder <stuart.yoder@....com>
To: Jarkko Sakkinen <jarkko@...nel.org>
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 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.

Thanks,
Stuart