domctl: handle XEN_DOMCTL_irq_permission without acquiring domctl lock

With dedicated locking added, the domctl lock isn't required here anymore.
Move the re-purposed (XSM_HOOK -> XSM_PRIV, as xsm_domctl() is now
bypassed) dedicated XSM checks as early as possible.

This is part of XSA-492.

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Acked-by: Daniel P. Smith <dpsmith@apertussolutions.com>
Reviewed-by: Roger Pau Monné <roger.pau@citrix.com>

xen/common/domctl.c

@@ -450,6 +450,36 @@ long do_domctl(XEN_GUEST_HANDLE_PARAM(xen_domctl_t) u_domctl)
         goto domctl_out_unlock_domonly;
     }
 
+    case XEN_DOMCTL_irq_permission:
+    {
+        unsigned int pirq = op->u.irq_permission.pirq, irq;
+        bool allow = op->u.irq_permission.allow_access;
+
+        ret = -EINVAL;
+        if ( pirq >= current->domain->nr_pirqs )
+            goto domctl_out_unlock_domonly;
+
+        irq = domain_pirq_to_irq(current->domain, pirq);
+
+        ret = -EPERM;
+        if ( irq )
+            ret = xsm_irq_permission(XSM_PRIV, d, irq, allow);
+        if ( ret )
+            goto domctl_out_unlock_domonly;
+
+        iocaps_double_lock(d, true);
+
+        if ( !irq_access_permitted(current->domain, irq) )
+            ret = -EPERM;
+        else if ( allow )
+            ret = irq_permit_access(d, irq);
+        else
+            ret = irq_deny_access(d, irq);
+
+        iocaps_double_unlock(d, true);
+        goto domctl_out_unlock_domonly;
+    }
+
     case XEN_DOMCTL_ioport_permission:
     case XEN_DOMCTL_ioport_mapping:
     case XEN_DOMCTL_bind_pt_irq:
@@ -783,31 +813,6 @@ long do_domctl(XEN_GUEST_HANDLE_PARAM(xen_domctl_t) u_domctl)
         }
         break;
 
-    case XEN_DOMCTL_irq_permission:
-    {
-        unsigned int pirq = op->u.irq_permission.pirq, irq;
-        int allow = op->u.irq_permission.allow_access;
-
-        if ( pirq >= current->domain->nr_pirqs )
-        {
-            ret = -EINVAL;
-            break;
-        }
-
-        iocaps_double_lock(d, true);
-
-        irq = pirq_access_permitted(current->domain, pirq);
-        if ( !irq || xsm_irq_permission(XSM_HOOK, d, irq, allow) )
-            ret = -EPERM;
-        else if ( allow )
-            ret = irq_permit_access(d, irq);
-        else
-            ret = irq_deny_access(d, irq);
-
-        iocaps_double_unlock(d, true);
-        break;
-    }
-
     case XEN_DOMCTL_settimeoffset:
         domain_set_time_offset(d, op->u.settimeoffset.time_offset_seconds);
         break;

xen/include/xsm/dummy.h

@@ -172,6 +172,7 @@ static XSM_INLINE int cf_check xsm_domctl(
     case XEN_DOMCTL_iomem_permission:
     case XEN_DOMCTL_ioport_mapping:
     case XEN_DOMCTL_ioport_permission:
+    case XEN_DOMCTL_irq_permission:
     case XEN_DOMCTL_memory_mapping:
     case XEN_DOMCTL_unbind_pt_irq:
         ASSERT_UNREACHABLE();
@@ -561,7 +562,7 @@ static XSM_INLINE int cf_check xsm_unmap_domain_irq(
 static XSM_INLINE int cf_check xsm_irq_permission(
     XSM_DEFAULT_ARG struct domain *d, int pirq, uint8_t allow)
 {
-    XSM_ASSERT_ACTION(XSM_HOOK);
+    XSM_ASSERT_ACTION(XSM_PRIV);
     return xsm_default_action(action, current->domain, d);
 }
 

xen/xsm/flask/hooks.c

@@ -684,6 +684,7 @@ static int cf_check flask_domctl(struct domain *d, unsigned int cmd,
     case XEN_DOMCTL_iomem_permission:
     case XEN_DOMCTL_ioport_mapping:
     case XEN_DOMCTL_ioport_permission:
+    case XEN_DOMCTL_irq_permission:
     case XEN_DOMCTL_memory_mapping:
     case XEN_DOMCTL_unbind_pt_irq:
         ASSERT_UNREACHABLE();
@@ -691,7 +692,6 @@ static int cf_check flask_domctl(struct domain *d, unsigned int cmd,
 
     /* These have individual XSM hooks (common/domctl.c) */
     case XEN_DOMCTL_scheduler_op:
-    case XEN_DOMCTL_irq_permission:
     case XEN_DOMCTL_set_target:
     case XEN_DOMCTL_vm_event_op: