qemu: cgroup: Expose /dev/sev/ only to domains that require SEV

SEV has a limit on number of concurrent guests. From security POV we
should only expose resources (any resources for that matter) to domains
that truly need them.
Signed-off-by: NErik Skultety <eskultet@redhat.com>
Reviewed-by: NDaniel P. Berrangé <berrange@redhat.com>

src/qemu/qemu_cgroup.c

@@ -691,6 +691,22 @@ qemuTeardownChardevCgroup(virDomainObjPtr vm,
 }
 
 
+static int
+qemuSetupSEVCgroup(virDomainObjPtr vm)
+{
+    qemuDomainObjPrivatePtr priv = vm->privateData;
+    int ret;
+
+    if (!virCgroupHasController(priv->cgroup, VIR_CGROUP_CONTROLLER_DEVICES))
+        return 0;
+
+    ret = virCgroupAllowDevicePath(priv->cgroup, "/dev/sev",
+                                   VIR_CGROUP_DEVICE_RW, false);
+    virDomainAuditCgroupPath(vm, priv->cgroup, "allow", "/dev/sev",
+                             "rw", ret);
+    return ret;
+}
+
 static int
 qemuSetupDevicesCgroup(virDomainObjPtr vm)
 {
@@ -798,6 +814,9 @@ qemuSetupDevicesCgroup(virDomainObjPtr vm)
             goto cleanup;
     }
 
+    if (vm->def->sev && qemuSetupSEVCgroup(vm) < 0)
+        goto cleanup;
+
     ret = 0;
  cleanup:
     virObjectUnref(cfg);