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David Alan Gilbert" , , , , , Brijesh Singh Subject: [PATCH v10 45/45] virt: sevguest: Add documentation for SEV-SNP CPUID Enforcement Date: Wed, 9 Feb 2022 12:10:39 -0600 Message-ID: <20220209181039.1262882-46-brijesh.singh@amd.com> X-Mailer: git-send-email 2.25.1 In-Reply-To: <20220209181039.1262882-1-brijesh.singh@amd.com> References: <20220209181039.1262882-1-brijesh.singh@amd.com> MIME-Version: 1.0 X-Originating-IP: [10.180.168.240] X-ClientProxiedBy: SATLEXMB04.amd.com (10.181.40.145) To SATLEXMB04.amd.com (10.181.40.145) X-EOPAttributedMessage: 0 X-MS-PublicTrafficType: Email X-MS-Office365-Filtering-Correlation-Id: 20b6ceb7-0422-48c1-778c-08d9ebf7c656 X-MS-TrafficTypeDiagnostic: DM6PR12MB4700:EE_ X-Microsoft-Antispam-PRVS: X-MS-Oob-TLC-OOBClassifiers: OLM:10000; X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0; X-Microsoft-Antispam-Message-Info: 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 X-Forefront-Antispam-Report: CIP:165.204.84.17; CTRY:US; LANG:en; SCL:1; SRV:; IPV:CAL; SFV:NSPM; H:SATLEXMB04.amd.com; PTR:InfoDomainNonexistent; CAT:NONE; SFS:(13230001)(4636009)(40470700004)(46966006)(36840700001)(5660300002)(47076005)(44832011)(36860700001)(2616005)(336012)(83380400001)(7696005)(26005)(36756003)(186003)(1076003)(54906003)(70206006)(70586007)(8676002)(7416002)(82310400004)(316002)(110136005)(6666004)(7406005)(86362001)(40460700003)(8936002)(426003)(508600001)(16526019)(356005)(4326008)(81166007)(2906002)(36900700001)(2101003); DIR:OUT; SFP:1101; X-OriginatorOrg: amd.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 09 Feb 2022 18:12:46.3672 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: 20b6ceb7-0422-48c1-778c-08d9ebf7c656 X-MS-Exchange-CrossTenant-Id: 3dd8961f-e488-4e60-8e11-a82d994e183d X-MS-Exchange-CrossTenant-OriginalAttributedTenantConnectingIp: TenantId=3dd8961f-e488-4e60-8e11-a82d994e183d; Ip=[165.204.84.17]; Helo=[SATLEXMB04.amd.com] X-MS-Exchange-CrossTenant-AuthSource: CO1NAM11FT068.eop-nam11.prod.protection.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: DM6PR12MB4700 Precedence: bulk List-ID: X-Mailing-List: linux-efi@vger.kernel.org From: Michael Roth Update the documentation with information regarding SEV-SNP CPUID Enforcement details and what sort of assurances it provides to guests. Signed-off-by: Michael Roth Signed-off-by: Brijesh Singh --- Documentation/virt/coco/sevguest.rst | 29 ++++++++++++++++++++++++++++ 1 file changed, 29 insertions(+) diff --git a/Documentation/virt/coco/sevguest.rst b/Documentation/virt/coco/sevguest.rst index 0f352056572d..48d66e10305b 100644 --- a/Documentation/virt/coco/sevguest.rst +++ b/Documentation/virt/coco/sevguest.rst @@ -118,6 +118,35 @@ be updated with the expected value. See GHCB specification for further detail on how to parse the certificate blob. +3. SEV-SNP CPUID Enforcement +============================ + +SEV-SNP guests can access a special page that contains a table of CPUID values +that have been validated by the PSP as part of the SNP_LAUNCH_UPDATE firmware +command. It provides the following assurances regarding the validity of CPUID +values: + + - Its address is obtained via bootloader/firmware (via CC blob), and those + binaries will be measured as part of the SEV-SNP attestation report. + - Its initial state will be encrypted/pvalidated, so attempts to modify + it during run-time will result in garbage being written, or #VC exceptions + being generated due to changes in validation state if the hypervisor tries + to swap the backing page. + - Attempts to bypass PSP checks by the hypervisor by using a normal page, or + a non-CPUID encrypted page will change the measurement provided by the + SEV-SNP attestation report. + - The CPUID page contents are *not* measured, but attempts to modify the + expected contents of a CPUID page as part of guest initialization will be + gated by the PSP CPUID enforcement policy checks performed on the page + during SNP_LAUNCH_UPDATE, and noticeable later if the guest owner + implements their own checks of the CPUID values. + +It is important to note that this last assurance is only useful if the kernel +has taken care to make use of the SEV-SNP CPUID throughout all stages of boot. +Otherwise, guest owner attestation provides no assurance that the kernel wasn't +fed incorrect values at some point during boot. + + Reference ---------