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    SubjectRe: [PATCH v8 28/40] KVM: SEV: Add documentation for SEV-SNP CPUID Enforcement
    On Fri, Dec 10, 2021 at 09:43:20AM -0600, Brijesh Singh wrote:
    > From: Michael Roth <michael.roth@amd.com>
    >
    > Update the documentation with SEV-SNP CPUID enforcement.
    >
    > Signed-off-by: Michael Roth <michael.roth@amd.com>
    > Signed-off-by: Brijesh Singh <brijesh.singh@amd.com>
    > ---
    > .../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
    ^
    the

    > +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.

    Unknown word [binares] in Documentation.
    Suggestions: ['binaries', 'Linares', 'bi nares', 'bi-nares', 'bin ares', 'bin-ares', 'nares']

    Also:

    s/whose binaries/and those binaries/

    > + - Its initial state will be encrypted/pvalidated, so attempts to modify
    > + it during run-time will be result in garbage being written, or #VC

    s/be //

    > + 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
    ^
    the

    > + 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
    >

    --
    Regards/Gruss,
    Boris.

    https://people.kernel.org/tglx/notes-about-netiquette

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