From patchwork Fri Feb 14 00:27:45 2025 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Stuart Yoder X-Patchwork-Id: 865113 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by smtp.subspace.kernel.org (Postfix) with ESMTP id C659CCA4E; Fri, 14 Feb 2025 00:27:58 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=217.140.110.172 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1739492880; cv=none; b=qWdhxj53AIYhvGjPOgtNkYhRJ3jpQvYIQmf/Q7xrBTDkYdoeJ8rwQ0/zdnCyfhK+ykQG2l4Viyu2pDClOEFA0FsF2BaJru5MKHA3nmT7YrXLodK6Y7goMAalpT3z32VltFe8Fy1uMhgd5y4wrbGinLH1mDl+OTxMXPfLcrhpoHk= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1739492880; c=relaxed/simple; bh=jUSUz00ESf+S26jtK/k3pKofGf7cV8jQzbW7nQEsROM=; h=From:To:Cc:Subject:Date:Message-Id:In-Reply-To:References: MIME-Version; b=l+FCfgNwqQRqCBXwsOJ4aUerSjut7UNXHrQ2T0k6GytsU5o34NwA78L/8bKTdFI/nLfYUu+1dHSHeCkYSKjzw7lNyPZoqJ8QmqiS2P7uff9cM4sK0WqDkJRY/EOz6I7hLgkjmfD5ewfr1WrMoAwhZKE1FMpee8dTMRZEuQgbJFs= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=arm.com; spf=pass smtp.mailfrom=arm.com; arc=none smtp.client-ip=217.140.110.172 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=arm.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=arm.com Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 855F4271B; Thu, 13 Feb 2025 16:28:16 -0800 (PST) Received: from beelzebub.ast.arm.com (u203013-lin.austin.arm.com [10.118.28.29]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPA id F37613F762; Thu, 13 Feb 2025 16:27:55 -0800 (PST) From: Stuart Yoder To: linux-integrity@vger.kernel.org, jarkko@kernel.org, peterhuewe@gmx.de, jgg@ziepe.ca, sudeep.holla@arm.com, rafael@kernel.org, lenb@kernel.org Cc: linux-acpi@vger.kernel.org, linux-kernel@vger.kernel.org Subject: [PATCH v3 5/5] Documentation: tpm: add documentation for the CRB FF-A interface Date: Thu, 13 Feb 2025 18:27:45 -0600 Message-Id: <20250214002745.878890-6-stuart.yoder@arm.com> X-Mailer: git-send-email 2.34.1 In-Reply-To: <20250214002745.878890-1-stuart.yoder@arm.com> References: <20250214002745.878890-1-stuart.yoder@arm.com> Precedence: bulk X-Mailing-List: linux-acpi@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 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/