[libvirt PATCH 08/12] tools: load CPU count and CPU SKU from libvirt

[Daniel P. Berrangé]

When validating a SEV-ES guest, we need to know the CPU count and VMSA
state. We can get the CPU count directly from libvirt's guest info. The
VMSA state can be constructed automatically if we query the CPU SKU from
host capabilities XML. Neither of these is secure, however, so this
behaviour is restricted.

Signed-off-by: Daniel P. Berrangé <berrange at redhat.com>
---
 docs/manpages/virt-qemu-sev-validate.rst |  4 ----
 tools/virt-qemu-sev-validate.py          | 23 +++++++++++++++++++++++
 2 files changed, 23 insertions(+), 4 deletions(-)

diff --git a/docs/manpages/virt-qemu-sev-validate.rst b/docs/manpages/virt-qemu-sev-validate.rst
index 7ba7323e13..fcc13d68c8 100644
--- a/docs/manpages/virt-qemu-sev-validate.rst
+++ b/docs/manpages/virt-qemu-sev-validate.rst
@@ -356,7 +356,6 @@ Validate the measurement of a SEV-ES SMP guest booting from disk:
 
    # virt-dom-sev-validate \
        --insecure \
-       --num-cpus 2 \
        --vmsa-cpu0 vmsa0.bin \
        --vmsa-cpu1 vmsa1.bin \
        --tk this-guest-tk.bin \
@@ -369,9 +368,6 @@ automatically constructed VMSA:
 
    # virt-dom-sev-validate \
        --insecure \
-       --cpu-family 23 \
-       --cpu-model 49 \
-       --cpu-stepping 0 \
        --tk this-guest-tk.bin \
        --domain fedora34x86_64
 
diff --git a/tools/virt-qemu-sev-validate.py b/tools/virt-qemu-sev-validate.py
index 2505aff07f..5da1353e60 100755
--- a/tools/virt-qemu-sev-validate.py
+++ b/tools/virt-qemu-sev-validate.py
@@ -869,6 +869,14 @@ class LibvirtConfidentialVM(ConfidentialVM):
         if self.policy is None:
             self.policy = sevinfo["sev-policy"]
 
+        if self.is_sev_es() and self.num_cpus is None:
+            if secure:
+                raise InsecureUsageException(
+                    "Using CPU count from guest is not secure")
+
+            info = self.dom.info()
+            self.num_cpus = info[3]
+
         if self.firmware is None:
             if remote:
                 raise UnsupportedUsageException(
@@ -914,6 +922,21 @@ class LibvirtConfidentialVM(ConfidentialVM):
                         "Using cmdline string from XML is not secure")
                 self.kernel_table.load_cmdline(cmdlinenodes[0].text)
 
+        capsxml = self.conn.getCapabilities()
+        capsdoc = etree.fromstring(capsxml)
+
+        if self.is_sev_es() and self.vmsa_cpu0 is None:
+            if secure:
+                raise InsecureUsageException(
+                    "Using CPU SKU from capabilities is not secure")
+
+            sig = capsdoc.xpath("/capabilities/host/cpu/signature")
+            if len(sig) == 1:
+                cpu_family = int(sig[0].get("family"))
+                cpu_model = int(sig[0].get("model"))
+                cpu_stepping = int(sig[0].get("stepping"))
+                self.build_vmsas(cpu_family, cpu_model, cpu_stepping)
+
 
 def parse_command_line():
     parser = argparse.ArgumentParser(
-- 
2.37.3