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From: Brijesh Singh <brijesh.singh@amd.com>
To: <x86@kernel.org>, <linux-kernel@vger.kernel.org>,
	<kvm@vger.kernel.org>, <linux-efi@vger.kernel.org>,
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Cc: Thomas Gleixner <tglx@linutronix.de>,
	Ingo Molnar <mingo@redhat.com>, Joerg Roedel <jroedel@suse.de>,
	Tom Lendacky <thomas.lendacky@amd.com>,
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	Michael Roth <michael.roth@amd.com>,
	Vlastimil Babka <vbabka@suse.cz>,
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	Andi Kleen <ak@linux.intel.com>,
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	<sathyanarayanan.kuppuswamy@linux.intel.com>,
	Brijesh Singh <brijesh.singh@amd.com>
Subject: [PATCH v10 45/45] virt: sevguest: Add documentation for SEV-SNP CPUID Enforcement
Date: Wed, 9 Feb 2022 12:10:39 -0600	[thread overview]
Message-ID: <20220209181039.1262882-46-brijesh.singh@amd.com> (raw)
In-Reply-To: <20220209181039.1262882-1-brijesh.singh@amd.com>

From: Michael Roth <michael.roth@amd.com>

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 <michael.roth@amd.com>
Signed-off-by: Brijesh Singh <brijesh.singh@amd.com>
---
 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
 ---------
 
-- 
2.25.1



      parent reply	other threads:[~2022-02-09 18:13 UTC|newest]

Thread overview: 57+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-02-09 18:09 [PATCH v10 00/45] Add AMD Secure Nested Paging (SEV-SNP) Guest Support Brijesh Singh
2022-02-09 18:09 ` [PATCH v10 01/45] KVM: SVM: Define sev_features and vmpl field in the VMSA Brijesh Singh
2022-02-09 18:09 ` [PATCH v10 02/45] KVM: SVM: Create a separate mapping for the SEV-ES save area Brijesh Singh
2022-02-09 18:09 ` [PATCH v10 03/45] KVM: SVM: Create a separate mapping for the GHCB " Brijesh Singh
2022-02-09 18:09 ` [PATCH v10 04/45] KVM: SVM: Update the SEV-ES save area mapping Brijesh Singh
2022-02-09 18:09 ` [PATCH v10 05/45] x86/boot: Introduce helpers for MSR reads/writes Brijesh Singh
2022-02-09 18:10 ` [PATCH v10 06/45] x86/boot: Use MSR read/write helpers instead of inline assembly Brijesh Singh
2022-02-09 18:10 ` [PATCH v10 07/45] x86/compressed/64: Detect/setup SEV/SME features earlier in boot Brijesh Singh
2022-02-09 18:10 ` [PATCH v10 08/45] x86/sev: " Brijesh Singh
2022-02-09 18:10 ` [PATCH v10 09/45] x86/mm: Extend cc_attr to include AMD SEV-SNP Brijesh Singh
2022-02-09 18:10 ` [PATCH v10 10/45] x86/sev: Define the Linux specific guest termination reasons Brijesh Singh
2022-02-09 18:10 ` [PATCH v10 11/45] x86/sev: Save the negotiated GHCB version Brijesh Singh
2022-02-09 18:10 ` [PATCH v10 12/45] x86/sev: Check SEV-SNP features support Brijesh Singh
2022-02-09 18:10 ` [PATCH v10 13/45] x86/sev: Add a helper for the PVALIDATE instruction Brijesh Singh
2022-02-09 18:10 ` [PATCH v10 14/45] x86/sev: Check the vmpl level Brijesh Singh
2022-02-09 18:10 ` [PATCH v10 15/45] x86/compressed: Add helper for validating pages in the decompression stage Brijesh Singh
2022-02-09 18:10 ` [PATCH v10 16/45] x86/compressed: Register GHCB memory when SEV-SNP is active Brijesh Singh
2022-02-09 18:10 ` [PATCH v10 17/45] x86/sev: " Brijesh Singh
2022-02-09 18:10 ` [PATCH v10 18/45] x86/sev: Add helper for validating pages in early enc attribute changes Brijesh Singh
2022-02-09 18:10 ` [PATCH v10 19/45] x86/kernel: Make the .bss..decrypted section shared in RMP table Brijesh Singh
2022-02-09 18:10 ` [PATCH v10 20/45] x86/kernel: Validate ROM memory before accessing when SEV-SNP is active Brijesh Singh
2022-02-09 18:10 ` [PATCH v10 21/45] x86/mm: Add support to validate memory when changing C-bit Brijesh Singh
2022-02-10 16:48   ` Borislav Petkov
2022-02-11 14:55   ` Borislav Petkov
2022-02-11 17:27     ` Brijesh Singh
2022-02-13 12:15       ` Borislav Petkov
2022-02-13 14:50         ` Tom Lendacky
2022-02-13 17:21           ` Borislav Petkov
2022-02-15 12:43         ` Kirill A. Shutemov
2022-02-15 12:54           ` Borislav Petkov
2022-02-15 13:15             ` Kirill A. Shutemov
2022-02-15 14:41               ` Borislav Petkov
2022-02-16 13:32     ` Borislav Petkov
2022-02-09 18:10 ` [PATCH v10 22/45] x86/sev: Use SEV-SNP AP creation to start secondary CPUs Brijesh Singh
2022-02-09 18:10 ` [PATCH v10 23/45] x86/head/64: Re-enable stack protection Brijesh Singh
2022-02-09 18:10 ` [PATCH v10 24/45] x86/compressed/acpi: Move EFI detection to helper Brijesh Singh
2022-02-09 18:10 ` [PATCH v10 25/45] x86/compressed/acpi: Move EFI system table lookup " Brijesh Singh
2022-02-09 18:10 ` [PATCH v10 26/45] x86/compressed/acpi: Move EFI config " Brijesh Singh
2022-02-09 18:10 ` [PATCH v10 27/45] x86/compressed/acpi: Move EFI vendor " Brijesh Singh
2022-02-09 18:10 ` [PATCH v10 28/45] x86/compressed/acpi: Move EFI kexec handling into common code Brijesh Singh
2022-02-09 18:10 ` [PATCH v10 29/45] x86/boot: Add Confidential Computing type to setup_data Brijesh Singh
2022-02-09 18:10 ` [PATCH v10 30/45] KVM: x86: Move lookup of indexed CPUID leafs to helper Brijesh Singh
2022-02-09 18:10 ` [PATCH v10 31/45] x86/sev: Move MSR-based VMGEXITs for CPUID " Brijesh Singh
2022-02-09 18:10 ` [PATCH v10 32/45] x86/compressed/64: Add support for SEV-SNP CPUID table in #VC handlers Brijesh Singh
2022-02-09 18:10 ` [PATCH v10 33/45] x86/boot: Add a pointer to Confidential Computing blob in bootparams Brijesh Singh
2022-02-09 18:10 ` [PATCH v10 34/45] x86/compressed: Add SEV-SNP feature detection/setup Brijesh Singh
2022-02-09 18:10 ` [PATCH v10 35/45] x86/compressed: Use firmware-validated CPUID leaves for SEV-SNP guests Brijesh Singh
2022-02-09 18:10 ` [PATCH v10 36/45] x86/compressed: Export and rename add_identity_map() Brijesh Singh
2022-02-09 18:10 ` [PATCH v10 37/45] x86/compressed/64: Add identity mapping for Confidential Computing blob Brijesh Singh
2022-02-09 18:10 ` [PATCH v10 38/45] x86/sev: Add SEV-SNP feature detection/setup Brijesh Singh
2022-02-09 18:10 ` [PATCH v10 39/45] x86/sev: Use firmware-validated CPUID for SEV-SNP guests Brijesh Singh
2022-02-09 18:10 ` [PATCH v10 40/45] x86/sev: Provide support for SNP guest request NAEs Brijesh Singh
2022-02-09 18:10 ` [PATCH v10 41/45] x86/sev: Register SEV-SNP guest request platform device Brijesh Singh
2022-02-09 18:10 ` [PATCH v10 42/45] virt: Add SEV-SNP guest driver Brijesh Singh
2022-02-09 18:10 ` [PATCH v10 43/45] virt: sevguest: Add support to derive key Brijesh Singh
2022-02-09 18:10 ` [PATCH v10 44/45] virt: sevguest: Add support to get extended report Brijesh Singh
2022-02-09 18:10 ` Brijesh Singh [this message]

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