diff -r a4eac162dcb9 xen/drivers/passthrough/vtd/dmar.c
--- a/xen/drivers/passthrough/vtd/dmar.c	Thu Mar 25 01:05:03 2010 +0800
+++ b/xen/drivers/passthrough/vtd/dmar.c	Fri Mar 26 01:59:55 2010 +0800
@@ -659,26 +659,71 @@ static int __init acpi_parse_dmar(struct
     while ( ((unsigned long)entry_header) <
             (((unsigned long)dmar) + table->length) )
     {
+        if ( entry_header->length < sizeof(struct acpi_dmar_entry_header) )
+        {
+            dprintk(XENLOG_ERR VTDPREFIX,
+                    "Invalid ACPI DMAR entry length: 0x%x\n",
+                    entry_header->length);
+            ret = -EINVAL;
+            break;
+        }
+
         switch ( entry_header->type )
         {
         case ACPI_DMAR_DRHD:
             if ( iommu_verbose )
                 dprintk(VTDPREFIX, "found ACPI_DMAR_DRHD:\n");
+
+            if ( entry_header->length < sizeof(struct acpi_table_drhd) )
+            {
+                dprintk(XENLOG_ERR VTDPREFIX,
+                        "  Invalid length: 0x%x\n", entry_header->length);
+                ret = -EINVAL;
+                break;
+            }
+
             ret = acpi_parse_one_drhd(entry_header);
             break;
         case ACPI_DMAR_RMRR:
             if ( iommu_verbose )
                 dprintk(VTDPREFIX, "found ACPI_DMAR_RMRR:\n");
+
+            if ( entry_header->length < sizeof(struct acpi_table_rmrr) )
+            {
+                dprintk(XENLOG_ERR VTDPREFIX,
+                        "  Invalid length: 0x%x\n", entry_header->length);
+                ret = -EINVAL;
+                break;
+            }
+
             ret = acpi_parse_one_rmrr(entry_header);
             break;
         case ACPI_DMAR_ATSR:
             if ( iommu_verbose )
                 dprintk(VTDPREFIX, "found ACPI_DMAR_ATSR:\n");
+
+            if ( entry_header->length < sizeof(struct acpi_table_atsr) )
+            {
+                dprintk(XENLOG_ERR VTDPREFIX,
+                        "  Invalid length: 0x%x\n", entry_header->length);
+                ret = -EINVAL;
+                break;
+            }
+
             ret = acpi_parse_one_atsr(entry_header);
             break;
         case ACPI_DMAR_RHSA:
             if ( iommu_verbose )
                 dprintk(VTDPREFIX, "found ACPI_DMAR_RHSA:\n");
+
+            if ( entry_header->length < sizeof(struct acpi_table_rhsa) )
+            {
+                dprintk(XENLOG_ERR VTDPREFIX,
+                        "  Invalid length: 0x%x\n", entry_header->length);
+                ret = -EINVAL;
+                break;
+            }
+
             ret = acpi_parse_one_rhsa(entry_header);
             break;
         default: