x86/HVM: prevent use-after-free when destroying a domain

hvm_domain_relinquish_resources() can free certain domain resources
which can still be accessed, e.g. by HVMOP_set_param, while the domain
is being cleaned up.

This is CVE-2015-0361 / XSA-116.

Signed-off-by: Mihai Donțu <mdontu@bitdefender.com>
Tested-by: Răzvan Cojocaru <rcojocaru@bitdefender.com>
Reviewed-by: Andrew Cooper <andrew.cooper3@citrix.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>

xen/arch/x86/hvm/hvm.c

@@ -1487,9 +1487,6 @@ int hvm_domain_initialise(struct domain *d)
 
 void hvm_domain_relinquish_resources(struct domain *d)
 {
-    xfree(d->arch.hvm_domain.io_handler);
-    xfree(d->arch.hvm_domain.params);
-
     if ( is_pvh_domain(d) )
         return;
 
@@ -1511,6 +1508,9 @@ void hvm_domain_relinquish_resources(struct domain *d)
 
 void hvm_domain_destroy(struct domain *d)
 {
+    xfree(d->arch.hvm_domain.io_handler);
+    xfree(d->arch.hvm_domain.params);
+
     hvm_destroy_cacheattr_region_list(d);
 
     if ( is_pvh_domain(d) )