x86: fix various issues with handling guest IRQs

- properly revoke IRQ access in map_domain_pirq() error path
- don't permit replacing an in use IRQ
- don't accept inputs in the GSI range for MAP_PIRQ_TYPE_MSI
- track IRQ access permission in host IRQ terms, not guest IRQ ones
  (and with that, also disallow Dom0 access to IRQ0)

This is CVE-2013-1919 / XSA-46.

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Acked-by: Stefano Stabellini <stefano.stabellini@eu.citrix.com>

tools/python/xen/xend/server/irqif.py

@@ -73,6 +73,12 @@ class IRQController(DevController):
        
         pirq = get_param('irq')
 
+        rc = xc.physdev_map_pirq(domid = self.getDomid(),
+                                 index = pirq,
+                                 pirq  = pirq)
+        if rc < 0:
+            raise VmError('irq: Failed to map irq %x' % (pirq))
+
         rc = xc.domain_irq_permission(domid        = self.getDomid(),
                                       pirq         = pirq,
                                       allow_access = True)
@@ -81,12 +87,6 @@ class IRQController(DevController):
             #todo non-fatal
             raise VmError(
                 'irq: Failed to configure irq: %d' % (pirq))
-        rc = xc.physdev_map_pirq(domid = self.getDomid(),
-                                index = pirq,
-                                pirq  = pirq)
-        if rc < 0:
-            raise VmError(
-                'irq: Failed to map irq %x' % (pirq))
         back = dict([(k, config[k]) for k in self.valid_cfg if k in config])
         return (self.allocateDeviceID(), back, {})