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| author | Michael Roth <michael.roth@amd.com> | 2022-02-24 17:56:25 +0100 |
|---|---|---|
| committer | Borislav Petkov <bp@suse.de> | 2022-04-07 16:47:12 +0200 |
| commit | 92a99584d965b930988b28f36d925bd9675828b3 (patch) | |
| tree | 769a0ecc3724b4480073f88007db79a6f4de47a3 /Documentation/virt | |
| parent | virt: sevguest: Add support to get extended report (diff) | |
| download | linux-92a99584d965b930988b28f36d925bd9675828b3.tar.xz linux-92a99584d965b930988b28f36d925bd9675828b3.zip | |
virt: sevguest: Add documentation for SEV-SNP CPUID Enforcement
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>
Signed-off-by: Borislav Petkov <bp@suse.de>
Link: https://lore.kernel.org/r/20220307213356.2797205-47-brijesh.singh@amd.com
Diffstat (limited to 'Documentation/virt')
| -rw-r--r-- | Documentation/virt/coco/sevguest.rst | 29 |
1 files changed, 29 insertions, 0 deletions
diff --git a/Documentation/virt/coco/sevguest.rst b/Documentation/virt/coco/sevguest.rst index 625de22658ec..bf593e88cfd9 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 --------- |