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David Alan Gilbert" , , , , Brijesh Singh Subject: [PATCH v7 33/45] KVM: SEV: Add documentation for SEV-SNP CPUID Enforcement Date: Wed, 10 Nov 2021 16:07:19 -0600 Message-ID: <20211110220731.2396491-34-brijesh.singh@amd.com> X-Mailer: git-send-email 2.25.1 In-Reply-To: <20211110220731.2396491-1-brijesh.singh@amd.com> References: <20211110220731.2396491-1-brijesh.singh@amd.com> Precedence: bulk X-Mailing-List: linux-coco@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Content-Type: text/plain X-Originating-IP: [10.180.168.240] X-ClientProxiedBy: SATLEXMB03.amd.com (10.181.40.144) To SATLEXMB04.amd.com (10.181.40.145) X-EOPAttributedMessage: 0 X-MS-PublicTrafficType: Email X-MS-Office365-Filtering-Correlation-Id: 8a4c6f45-4b77-4863-e1cb-08d9a496b0d4 X-MS-TrafficTypeDiagnostic: BL0PR12MB4612: 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:(4636009)(36840700001)(46966006)(7416002)(81166007)(8676002)(70586007)(508600001)(86362001)(70206006)(7406005)(7696005)(8936002)(316002)(356005)(110136005)(54906003)(83380400001)(82310400003)(2906002)(5660300002)(4326008)(2616005)(426003)(36860700001)(16526019)(26005)(36756003)(186003)(336012)(44832011)(6666004)(47076005)(1076003)(36900700001)(2101003);DIR:OUT;SFP:1101; X-OriginatorOrg: amd.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 10 Nov 2021 22:08:56.7627 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: 8a4c6f45-4b77-4863-e1cb-08d9a496b0d4 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: DM6NAM11FT022.eop-nam11.prod.protection.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: BL0PR12MB4612 From: Michael Roth Update the documentation with SEV-SNP CPUID enforcement. Signed-off-by: Michael Roth Signed-off-by: Brijesh Singh --- .../virt/kvm/amd-memory-encryption.rst | 28 +++++++++++++++++++ 1 file changed, 28 insertions(+) diff --git a/Documentation/virt/kvm/amd-memory-encryption.rst b/Documentation/virt/kvm/amd-memory-encryption.rst index 5c081c8c7164..aa8292fa579a 100644 --- a/Documentation/virt/kvm/amd-memory-encryption.rst +++ b/Documentation/virt/kvm/amd-memory-encryption.rst @@ -427,6 +427,34 @@ issued by the hypervisor to make the guest ready for execution. Returns: 0 on success, -negative on error +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 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), whose + binares 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 be 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 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. + References ========== -- 2.25.1