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David Alan Gilbert" , , , , , Brijesh Singh Subject: [PATCH v9 30/43] KVM: SEV: Add documentation for SEV-SNP CPUID Enforcement Date: Fri, 28 Jan 2022 11:17:51 -0600 Message-ID: <20220128171804.569796-31-brijesh.singh@amd.com> X-Mailer: git-send-email 2.25.1 In-Reply-To: <20220128171804.569796-1-brijesh.singh@amd.com> References: <20220128171804.569796-1-brijesh.singh@amd.com> 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: 09a9c17a-176c-4f84-25ab-08d9e2824b3b X-MS-TrafficTypeDiagnostic: MN2PR12MB2863: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:(4636009)(46966006)(36840700001)(40470700004)(44832011)(426003)(4326008)(81166007)(316002)(5660300002)(54906003)(70206006)(83380400001)(336012)(70586007)(508600001)(86362001)(26005)(110136005)(186003)(16526019)(82310400004)(8936002)(36860700001)(7696005)(7416002)(2616005)(36756003)(6666004)(8676002)(40460700003)(47076005)(356005)(7406005)(2906002)(1076003)(36900700001)(2101003);DIR:OUT;SFP:1101; X-OriginatorOrg: amd.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 28 Jan 2022 17:19:08.4179 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: 09a9c17a-176c-4f84-25ab-08d9e2824b3b 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: DM6NAM11FT006.eop-nam11.prod.protection.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: MN2PR12MB2863 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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 1c6847fff304..0c72f44cc11a 100644 --- a/Documentation/virt/kvm/amd-memory-encryption.rst +++ b/Documentation/virt/kvm/amd-memory-encryption.rst @@ -433,6 +433,34 @@ 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 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. + References ========== -- 2.25.1