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David Alan Gilbert" , , , , , Brijesh Singh Subject: [PATCH v11 45/45] virt: sevguest: Add documentation for SEV-SNP CPUID Enforcement Date: Thu, 24 Feb 2022 10:56:25 -0600 Message-ID: <20220224165625.2175020-46-brijesh.singh@amd.com> X-Mailer: git-send-email 2.25.1 In-Reply-To: <20220224165625.2175020-1-brijesh.singh@amd.com> References: <20220224165625.2175020-1-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: 5aefc08b-9bea-4e07-037a-08d9f7b6fc90 X-MS-TrafficTypeDiagnostic: BL0PR12MB2514:EE_ X-Microsoft-Antispam-PRVS: 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)(46966006)(40470700004)(36840700001)(47076005)(356005)(316002)(426003)(36860700001)(40460700003)(336012)(26005)(2616005)(1076003)(186003)(54906003)(110136005)(81166007)(2906002)(7416002)(4326008)(86362001)(82310400004)(7406005)(70206006)(7696005)(8676002)(8936002)(5660300002)(508600001)(16526019)(36756003)(83380400001)(44832011)(70586007)(6666004)(36900700001)(2101003);DIR:OUT;SFP:1101; X-OriginatorOrg: amd.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 24 Feb 2022 16:59:14.1947 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: 5aefc08b-9bea-4e07-037a-08d9f7b6fc90 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: DM6NAM11FT034.eop-nam11.prod.protection.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: BL0PR12MB2514 X-Rspamd-Server: rspam01 X-Rspamd-Queue-Id: BCA8040017 X-Rspam-User: Authentication-Results: imf04.hostedemail.com; dkim=pass header.d=amd.com header.s=selector1 header.b=B+wSRBWR; spf=pass (imf04.hostedemail.com: domain of brijesh.singh@amd.com designates 40.107.237.55 as permitted sender) smtp.mailfrom=brijesh.singh@amd.com; dmarc=pass (policy=quarantine) header.from=amd.com X-Stat-Signature: 63n6dy5oo6dxojfijm38439mykx6nn1s X-HE-Tag: 1645721956-328098 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: 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 ---------