KVM: SEV: Add KVM_SEV_SNP_LAUNCH_UPDATE command

A key aspect of a launching an SNP guest is initializing it with a
known/measured payload which is then encrypted into guest memory as
pre-validated private pages and then measured into the cryptographic
launch context created with KVM_SEV_SNP_LAUNCH_START so that the guest
can attest itself after booting.

Since all private pages are provided by guest_memfd, make use of the
kvm_gmem_populate() interface to handle this. The general flow is that
guest_memfd will handle allocating the pages associated with the GPA
ranges being initialized by each particular call of
KVM_SEV_SNP_LAUNCH_UPDATE, copying data from userspace into those pages,
and then the post_populate callback will do the work of setting the
RMP entries for these pages to private and issuing the SNP firmware
calls to encrypt/measure them.

For more information see the SEV-SNP specification.

Signed-off-by: Brijesh Singh <brijesh.singh@amd.com>
Co-developed-by: Michael Roth <michael.roth@amd.com>
Signed-off-by: Michael Roth <michael.roth@amd.com>
Signed-off-by: Ashish Kalra <ashish.kalra@amd.com>
Message-ID: <20240501085210.2213060-7-michael.roth@amd.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

1 files changed, 54 insertions, 0 deletions

diff --git a/Documentation/virt/kvm/x86/amd-memory-encryption.rst b/Documentation/virt/kvm/x86/amd-memory-encryption.rst
index dd179e162a87..cc16a7426d18 100644
--- a/Documentation/virt/kvm/x86/amd-memory-encryption.rst
+++ b/Documentation/virt/kvm/x86/amd-memory-encryption.rst
@@ -490,6 +490,60 @@ Returns: 0 on success, -negative on error
 See SNP_LAUNCH_START in the SEV-SNP specification [snp-fw-abi]_ for further
 details on the input parameters in ``struct kvm_sev_snp_launch_start``.
 
+19. KVM_SEV_SNP_LAUNCH_UPDATE
+-----------------------------
+
+The KVM_SEV_SNP_LAUNCH_UPDATE command is used for loading userspace-provided
+data into a guest GPA range, measuring the contents into the SNP guest context
+created by KVM_SEV_SNP_LAUNCH_START, and then encrypting/validating that GPA
+range so that it will be immediately readable using the encryption key
+associated with the guest context once it is booted, after which point it can
+attest the measurement associated with its context before unlocking any
+secrets.
+
+It is required that the GPA ranges initialized by this command have had the
+KVM_MEMORY_ATTRIBUTE_PRIVATE attribute set in advance. See the documentation
+for KVM_SET_MEMORY_ATTRIBUTES for more details on this aspect.
+
+Upon success, this command is not guaranteed to have processed the entire
+range requested. Instead, the ``gfn_start``, ``uaddr``, and ``len`` fields of
+``struct kvm_sev_snp_launch_update`` will be updated to correspond to the
+remaining range that has yet to be processed. The caller should continue
+calling this command until those fields indicate the entire range has been
+processed, e.g. ``len`` is 0, ``gfn_start`` is equal to the last GFN in the
+range plus 1, and ``uaddr`` is the last byte of the userspace-provided source
+buffer address plus 1. In the case where ``type`` is KVM_SEV_SNP_PAGE_TYPE_ZERO,
+``uaddr`` will be ignored completely.
+
+Parameters (in): struct  kvm_sev_snp_launch_update
+
+Returns: 0 on success, < 0 on error, -EAGAIN if caller should retry
+
+::
+
+        struct kvm_sev_snp_launch_update {
+                __u64 gfn_start;        /* Guest page number to load/encrypt data into. */
+                __u64 uaddr;            /* Userspace address of data to be loaded/encrypted. */
+                __u64 len;              /* 4k-aligned length in bytes to copy into guest memory.*/
+                __u8 type;              /* The type of the guest pages being initialized. */
+                __u8 pad0;
+                __u16 flags;            /* Must be zero. */
+                __u32 pad1;
+                __u64 pad2[4];
+
+        };
+
+where the allowed values for page_type are #define'd as::
+
+        KVM_SEV_SNP_PAGE_TYPE_NORMAL
+        KVM_SEV_SNP_PAGE_TYPE_ZERO
+        KVM_SEV_SNP_PAGE_TYPE_UNMEASURED
+        KVM_SEV_SNP_PAGE_TYPE_SECRETS
+        KVM_SEV_SNP_PAGE_TYPE_CPUID
+
+See the SEV-SNP spec [snp-fw-abi]_ for further details on how each page type is
+used/measured.
+
 Device attribute API
 ====================