tools: load direct kernel config from libvirt

When connected to libvirt we can validate that the guest configuration
has the kernel hashes property enabled, otherwise including the kernel
GUID table in our expected measurements is not likely to match the
actual measurement.

When running locally we can also automatically detect the kernel/initrd
paths, along with the cmdline string from the XML.

Reviewed-by: Cole Robinson <crobinso@redhat.com>
Reviewed-by: Ján Tomko <jtomko@redhat.com>
Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>

docs/manpages/virt-qemu-sev-validate.rst

@@ -265,6 +265,15 @@ Validate the measurement of a SEV guest booting from disk:
        --tk this-guest-tk.bin \
        --domain fedora34x86_64
 
+Validate the measurement of a SEV guest with direct kernel boot:
+
+::
+
+   # virt-dom-sev-validate \
+       --insecure \
+       --tk this-guest-tk.bin \
+       --domain fedora34x86_64
+
 EXIT STATUS
 ===========
 

tools/virt-qemu-sev-validate

@@ -300,6 +300,35 @@ class LibvirtConfidentialVM(ConfidentialVM):
             raise IncorrectConfigException(
                 "Domain must have one firmware path")
 
+        measure_kernel_nodes = doc.xpath(
+            "/domain/launchSecurity[@type='sev']/@kernelHashes")
+        measure_kernel = False
+        if len(measure_kernel_nodes) == 1:
+            if measure_kernel_nodes[0] == "yes":
+                measure_kernel = True
+
+        xp_kernel = "/domain/os/kernel"
+        xp_initrd = "/domain/os/initrd"
+        xp_cmdline = "/domain/os/cmdline"
+        kern_nodes = (doc.xpath(xp_kernel) +
+                      doc.xpath(xp_initrd) +
+                      doc.xpath(xp_cmdline))
+        if not measure_kernel:
+            if len(self.kernel_table.entries()) != 0:
+                raise UnsupportedUsageException(
+                    "kernel/initrd/cmdline provided but kernel "
+                    "measurement not enabled")
+
+            # Check for an insecure scenario
+            if len(kern_nodes) != 0 and secure:
+                raise InsecureUsageException(
+                    "direct kernel boot present without measurement")
+        else:
+            if len(kern_nodes) == 0:
+                raise IncorrectConfigException(
+                    "kernel/initrd/cmdline not provided but kernel "
+                    "measurement is enabled")
+
     def load_domain(self, uri, id_name_uuid, secure, ignore_config):
         self.conn = libvirt.open(uri)
 
@@ -368,6 +397,36 @@ class LibvirtConfidentialVM(ConfidentialVM):
 
             self.load_firmware(loadernodes[0].text)
 
+        if self.kernel_table.kernel is None:
+            kernelnodes = doc.xpath("/domain/os/kernel")
+            if len(kernelnodes) != 0:
+                if remote:
+                    raise UnsupportedUsageException(
+                        "Cannot access kernel path remotely")
+                if secure:
+                    raise InsecureUsageException(
+                        "Using kernel path from XML is not secure")
+                self.kernel_table.load_kernel(kernelnodes[0].text)
+
+        if self.kernel_table.initrd is None:
+            initrdnodes = doc.xpath("/domain/os/initrd")
+            if len(initrdnodes) != 0:
+                if remote:
+                    raise UnsupportedUsageException(
+                        "Cannot access initrd path remotely")
+                if secure:
+                    raise InsecureUsageException(
+                        "Using initrd path from XML is not secure")
+                self.kernel_table.load_initrd(initrdnodes[0].text)
+
+        if self.kernel_table.cmdline is None:
+            cmdlinenodes = doc.xpath("/domain/os/cmdline")
+            if len(cmdlinenodes) != 0:
+                if secure:
+                    raise InsecureUsageException(
+                        "Using cmdline string from XML is not secure")
+                self.kernel_table.load_cmdline(cmdlinenodes[0].text)
+
 
 def parse_command_line():
     parser = argparse.ArgumentParser(