[Xen-devel] xen: Clear IRQ_GUEST bit from irq_desc status if its action is NULL

[Igor Mammedov <imammedo@xxxxxxxxxx>]

On a system with Intel C600 series Patsburg SAS controller
if following command are executed:

  rmmod isci
  modprobe isci

the host will crash in pirq_guest_bind in attempt to dereference
NULL action pointer.

This is caused by isci driver which does not cleanup irq properly,
removing device first and then os tries to unbind its irqs afterwards.

c/s 20093 and 20844 fixed host crashes when removing isci module.

However in dynamic_irq_cleanup 'action' field of irq_desc is set to
NULL but IRQ_GUEST flag in 'status' field is not cleared. So on next
attempt to bind pirq (modprobe isci) with IRQ_GUEST flag set, branch
  if ( !(desc->status & IRQ_GUEST) )
is skipped and host ends up with dereferencing NULL pointer 'action'.

Second hunk is a bit of code cleanup, removing duplicate code and keeps
IRQ_GUEST flag reset at one place.

Please review.

Signed-off-by: Igor Mammedov <imammedo@xxxxxxxxxx>

diff -r 0312575dc35e xen/arch/x86/irq.c
--- a/xen/arch/x86/irq.c        Thu Sep 08 15:13:06 2011 +0100
+++ b/xen/arch/x86/irq.c        Tue Sep 13 09:27:12 2011 +0200
@@ -1472,6 +1472,7 @@ static irq_guest_action_t *__pirq_guest_
 
     if ( unlikely(action == NULL) )
     {
+        desc->status &= ~IRQ_GUEST;
         dprintk(XENLOG_G_WARNING, "dom%d: pirq %d: desc->action is NULL!\n",
                 d->domain_id, pirq->pirq);
         return NULL;
@@ -1598,17 +1599,14 @@ static int pirq_guest_force_unbind(struc
 
     action = (irq_guest_action_t *)desc->action;
     if ( unlikely(action == NULL) )
-    {
-        dprintk(XENLOG_G_WARNING, "dom%d: pirq %d: desc->action is NULL!\n",
-            d->domain_id, pirq->pirq);
-        goto out;
-    }
+        goto unbind;
 
     for ( i = 0; (i < action->nr_guests) && (action->guest[i] != d); i++ )
         continue;
     if ( i == action->nr_guests )
         goto out;
 
+ unbind:
     bound = 1;
     oldaction = __pirq_guest_unbind(d, pirq, desc);
 

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