MSI-X: avoid array overrun upon MSI-X table writes

pt_msix_init() allocates msix->msix_entry[] to just cover
msix->total_entries entries. While pci_msix_readl() resorts to reading
physical memory for out of bounds reads, pci_msix_writel() so far
simply accessed/corrupted unrelated memory.

pt_iomem_map()'s call to cpu_register_physical_memory() registers a
page granular region, which is necessary as the Pending Bit Array may
share space with the MSI-X table (but nothing else is allowed to). This
also explains why pci_msix_readl() actually honors out of bounds reads,
but pci_msi_writel() doesn't need to.

This is XSA-164.

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Acked-by: Ian Campbell <ian.campbell@citrix.com>

--- a/tools/qemu-xen-traditional/hw/pt-msi.c
+++ b/tools/qemu-xen-traditional/hw/pt-msi.c
@@ -440,6 +440,13 @@ static void pci_msix_writel(void *opaque
         return;
     }
 
+    if ( addr - msix->mmio_base_addr >= msix->total_entries * 16 )
+    {
+        PT_LOG("Error: Out of bounds write to MSI-X table,"
+               " addr %016"PRIx64"\n", addr);
+        return;
+    }
+
     entry_nr = (addr - msix->mmio_base_addr) / 16;
     entry = &msix->msix_entry[entry_nr];
     offset = ((addr - msix->mmio_base_addr) % 16) / 4;