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David Alan Gilbert" , , , , Brijesh Singh Subject: [PATCH v8 28/40] KVM: SEV: Add documentation for SEV-SNP CPUID Enforcement Date: Fri, 10 Dec 2021 09:43:20 -0600 Message-ID: <20211210154332.11526-29-brijesh.singh@amd.com> X-Mailer: git-send-email 2.25.1 In-Reply-To: <20211210154332.11526-1-brijesh.singh@amd.com> References: <20211210154332.11526-1-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 SATLEXMB03.amd.com (10.181.40.144) X-EOPAttributedMessage: 0 X-MS-PublicTrafficType: Email X-MS-Office365-Filtering-Correlation-Id: 0ff5ff79-c7f7-4324-0646-08d9bbf3f6e5 X-MS-TrafficTypeDiagnostic: BY5PR12MB4211: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:SATLEXMB03.amd.com;PTR:InfoDomainNonexistent;CAT:NONE;SFS:(4636009)(36840700001)(46966006)(40470700001)(86362001)(508600001)(47076005)(1076003)(6666004)(2906002)(81166007)(316002)(82310400004)(356005)(36756003)(110136005)(40460700001)(54906003)(44832011)(2616005)(426003)(83380400001)(186003)(16526019)(336012)(26005)(70206006)(70586007)(7696005)(36860700001)(4326008)(5660300002)(8676002)(7406005)(7416002)(8936002)(36900700001)(2101003);DIR:OUT;SFP:1101; X-OriginatorOrg: amd.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 10 Dec 2021 15:44:34.2818 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: 0ff5ff79-c7f7-4324-0646-08d9bbf3f6e5 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=[SATLEXMB03.amd.com] X-MS-Exchange-CrossTenant-AuthSource: BN8NAM11FT007.eop-nam11.prod.protection.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: BY5PR12MB4211 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 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