The SEV-ES boot measurement includes the initial CPU register state
(VMSA) and one of the fields includes the CPU identification. When
building a VMSA blob we get the CPU family/model/stepping from the
host capabilities, however, the VMSA must reflect the guest CPU not
host CPU. Thus using host capabilities is only when whe the guest
has the 'host-passthrough' CPU mode active. With 'host-model' it is
cannot be assumed host and guest match, because QEMU may not (yet)
have a named CPU model for a given host CPU.
Signed-off-by: Daniel P. Berrangé <berrange@xxxxxxxxxx>
---
tools/virt-qemu-sev-validate | 5 +++++
1 file changed, 5 insertions(+)
diff --git a/tools/virt-qemu-sev-validate b/tools/virt-qemu-sev-validate
index 209f19a4a8..c279741004 100755
--- a/tools/virt-qemu-sev-validate
+++ b/tools/virt-qemu-sev-validate
@@ -1054,6 +1054,11 @@ class LibvirtConfidentialVM(ConfidentialVM):
raise InsecureUsageException(
"Using CPU SKU from capabilities is not secure")
+ mode = doc.xpath("/domain/cpu/@mode")
+ if mode != "host-passthrough":
+ raise UnsupportedUsageException(
+ "Using CPU family/model/stepping from host not possible unless 'host-passthrough' is used")
+
sig = capsdoc.xpath("/capabilities/host/cpu/signature")
if len(sig) != 1:
raise UnsupportedUsageException(
--
2.41.0
