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.

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>

--- a/xen/arch/x86/hvm/hvm.c
+++ b/xen/arch/x86/hvm/hvm.c
@@ -602,13 +602,13 @@ void hvm_domain_relinquish_resources(str
         hpet_deinit(d);
     }
 
-    xfree(d->arch.hvm_domain.io_handler);
-    xfree(d->arch.hvm_domain.params);
     xfree(d->arch.hvm_domain.pbuf);
 }
 
 void hvm_domain_destroy(struct domain *d)
 {
+    xfree(d->arch.hvm_domain.io_handler);
+    xfree(d->arch.hvm_domain.params);
     hvm_funcs.domain_destroy(d);
     rtc_deinit(d);
     stdvga_deinit(d);