From: Jan Beulich <jbeulich@suse.com>
Subject: x86: don't allow MSI pIRQ mapping on unowned device

MSI setup should be permitted only for existing devices owned by the
respective guest (the operation may still be carried out by the domain
controlling that guest).

This is part of XSA-237.

Reported-by: HW42 <hw42@ipsumj.de>
Signed-off-by: Jan Beulich <jbeulich@suse.com>
Reviewed-by: Andrew Cooper <andrew.cooper3@citrix.com>

--- a/xen/arch/x86/irq.c
+++ b/xen/arch/x86/irq.c
@@ -1964,7 +1964,10 @@ int map_domain_pirq(
         if ( !cpu_has_apic )
             goto done;
 
-        pdev = pci_get_pdev(msi->seg, msi->bus, msi->devfn);
+        pdev = pci_get_pdev_by_domain(d, msi->seg, msi->bus, msi->devfn);
+        if ( !pdev )
+            goto done;
+
         ret = pci_enable_msi(msi, &msi_desc);
         if ( ret )
         {