conf: add support for setting SEV kernel hashes

Normally the SEV measurement only covers the firmware
loader contents. When doing a direct kernel boot, however,
with new enough OVMF it is possible to ask for the
measurement to cover the kernel, ramdisk and command line.

It can't be done automatically as that would break existing
guests using direct kernel boot with old firmware, so there
is a new XML setting allowing this behaviour to be toggled.

Reviewed-by: Peter Krempa <pkrempa@redhat.com>
Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>

docs/formatdomain.rst

@@ -8222,7 +8222,7 @@ spec <https://support.amd.com/TechDocs/55766_SEV-KM_API_Specification.pdf>`__
 
    <domain>
      ...
-     <launchSecurity type='sev'>
+     <launchSecurity type='sev' kernelHashes='yes'>
        <policy>0x0001</policy>
        <cbitpos>47</cbitpos>
        <reducedPhysBits>1</reducedPhysBits>
@@ -8232,6 +8232,11 @@ spec <https://support.amd.com/TechDocs/55766_SEV-KM_API_Specification.pdf>`__
      ...
    </domain>
 
+``kernelHashes``
+   The optional ``kernelHashes`` attribute indicates whether the
+   hashes of the kernel, ramdisk and command line should be included
+   in the measurement done by the firmware. This is only valid if
+   using direct kernel boot. :since:`Since 8.0.0`
 ``cbitpos``
    The required ``cbitpos`` element provides the C-bit (aka encryption bit)
    location in guest page table entry. The value of ``cbitpos`` is hypervisor

docs/schemas/domaincommon.rng

@@ -499,6 +499,11 @@
     <attribute name="type">
       <value>sev</value>
     </attribute>
+    <optional>
+      <attribute name="kernelHashes">
+        <ref name="virYesNo"/>
+      </attribute>
+    </optional>
     <interleave>
       <optional>
         <element name="cbitpos">

src/conf/domain_conf.c

@@ -14804,6 +14804,10 @@ virDomainSEVDefParseXML(virDomainSEVDef *def,
     unsigned long policy;
     int rc;
 
+    if (virXMLPropTristateBool(ctxt->node, "kernelHashes", VIR_XML_PROP_NONE,
+                               &def->kernel_hashes) < 0)
+        return -1;
+
     if (virXPathULongHex("string(./policy)", ctxt, &policy) < 0) {
         virReportError(VIR_ERR_XML_ERROR, "%s",
                        _("failed to get launch security policy"));
@@ -27134,6 +27138,10 @@ virDomainSecDefFormat(virBuffer *buf, virDomainSecDef *sec)
     case VIR_DOMAIN_LAUNCH_SECURITY_SEV: {
         virDomainSEVDef *sev = &sec->data.sev;
 
+        if (sev->kernel_hashes != VIR_TRISTATE_BOOL_ABSENT)
+            virBufferAsprintf(&attrBuf, " kernelHashes='%s'",
+                              virTristateBoolTypeToString(sev->kernel_hashes));
+
         if (sev->haveCbitpos)
             virBufferAsprintf(&childBuf, "<cbitpos>%d</cbitpos>\n", sev->cbitpos);
 

src/conf/domain_conf.h

@@ -2714,6 +2714,7 @@ struct _virDomainSEVDef {
     unsigned int cbitpos;
     bool haveReducedPhysBits;
     unsigned int reduced_phys_bits;
+    virTristateBool kernel_hashes;
 };
 
 struct _virDomainSecDef {