From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id B55951EB1A3; Thu, 20 Feb 2025 09:30:20 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1740043820; cv=none; b=Q/yrGcR6CvsWSOwn71eUwQOzIjV73CGzuGmnrvyn4jaUaE4WBj8oS/WqeFsfDaf6HC0+nwtPEhLNlMgYVIsJrrUx0Mrjmo5CUg18NGyRrF0E2ltAIANHPAc8yiqAHHnsUx6JbFRPP7OncKvVHP0q4/N9sP7PJLaiHRYZKi1xQl4= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1740043820; c=relaxed/simple; bh=F8sHSdDiGOAJStv8uxWi3qIBaQqEJ20QIqAF2G4aNec=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=P94svss+45p8j66U3TKzk1stiiT1Z+HbfQhJgNHvbTBWEXaZDKxN+mDA125SlKyNjgSqV1SMllJhu33lDkey4lXAkyUfJ9QFE7PBcNpDvTEEm+vTdBJCHpn64YB8fYadWaEqKl6m3adX/pjL2JTWztU/37gW8CpzY/BKevZFSLA= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=VKkoeuA7; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="VKkoeuA7" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 9F1EEC4CED1; Thu, 20 Feb 2025 09:30:19 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1740043820; bh=F8sHSdDiGOAJStv8uxWi3qIBaQqEJ20QIqAF2G4aNec=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=VKkoeuA7ttTVhU/uyGYvLRshRKIqN1hK2wJJkKBWeNkhAfkJ1AsmF/RtTObeW2gd9 MvMmpJsWx1e99aZeDmLWT5XI62lsZxTYvQcxJLGyHS1K4Hxb4dW4d7Xw+q2OI7WMLG DEounBqCvzK7uE9r6xqjT/TV4CRJX9Wz/f8M7Tly4Y5JhnVy+4wS9u2GVGtKIEMJaE gGTEdynnYC+ifkLNV/tyeUrLKbCnRVpwU4ZgZP5qXYYF6oVaizwm2iF7n/IgxZNmA0 scFHivLr85VXX2kJWmcp87dirkSOVI9pM4H+fHyBye4BTcMvmYU+yACg0esXpmcrXi gXPUjiuKh538A== Date: Thu, 20 Feb 2025 11:30:15 +0200 From: Jarkko Sakkinen To: Stuart Yoder Cc: linux-integrity@vger.kernel.org, peterhuewe@gmx.de, jgg@ziepe.ca, sudeep.holla@arm.com, rafael@kernel.org, lenb@kernel.org, linux-acpi@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v5 5/5] Documentation: tpm: add documentation for the CRB FF-A interface Message-ID: References: <20250219201014.174344-1-stuart.yoder@arm.com> <20250219201014.174344-6-stuart.yoder@arm.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20250219201014.174344-6-stuart.yoder@arm.com> On Wed, Feb 19, 2025 at 02:10:14PM -0600, Stuart Yoder wrote: > Add documentation providing details of how the CRB driver interacts > with FF-A. > > Signed-off-by: Stuart Yoder > --- > 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..0184193da3c7 > --- /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) > + > +- Provide a standard interface for software components in the Non-secure > + state, for example OS and Hypervisors, to communicate with this firmware. > + > +A TPM can be implemented as an FF-A secure service. This could be a firmware > +TPM or could potentially be a TPM service that acts as a proxy to a discrete > +TPM chip. An FF-A based TPM abstracts hardware details (e.g. bus controller > +and chip selects) away from the OS and can protect locality 4 from access > +by an OS. The TCG-defined CRB interface is used by clients to interact > +with the TPM service. > + > +The Arm TPM Service Command Response Buffer Interface Over FF-A [3]_ > +specification defines FF-A messages that can be used by a client to signal > +when updates have been made to the CRB. > + > +How the Linux CRB driver interacts with FF-A is summarized below: > + > +- The tpm_crb_ffa driver registers with the FF-A subsystem in the kernel > + with an architected TPM service UUID defined in the CRB over FF-A spec. > + > +- If a TPM service is discovered by FF-A, the probe() function in the > + tpm_crb_ffa driver runs, and the driver initializes. > + > +- The probing and initialization of the Linux CRB driver is triggered > + by the discovery of a TPM advertised via ACPI. The CRB driver can > + detect the type of TPM through the ACPI 'start' method. The start > + method for Arm FF-A was defined in TCG ACPI v1.4 [4]_. > + > +- When the CRB driver performs its normal functions such as signaling 'start' > + and locality request/relinquish it invokes the tpm_crb_ffa_start() funnction > + in the tpm_crb_ffa driver which handles the FF-A messaging to the TPM. > + > +References > +========== > + > +.. [1] **TCG PC Client Platform TPM Profile (PTP) Specification** > + https://trustedcomputinggroup.org/resource/pc-client-platform-tpm-profile-ptp-specification/ > +.. [2] **Arm Firmware Framework for Arm A-profile (FF-A)** > + https://developer.arm.com/documentation/den0077/latest/ > +.. [3] **Arm TPM Service Command Response Buffer Interface Over FF-A** > + https://developer.arm.com/documentation/den0138/latest/ > +.. [4] **TCG ACPI Specification** > + https://trustedcomputinggroup.org/resource/tcg-acpi-specification/ > -- > 2.34.1 > Reviewed-by: Jarkko Sakkinen BR, Jarkko