VT-d: protect against bogus information coming from BIOS

Add checks similar to those done by Linux: The DRHD address must not
be all zeros or all ones (Linux only checks for zero), and capabilities
as well as extended capabilities must not be all ones.

Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>

--- a/xen/drivers/passthrough/vtd/dmar.c
+++ b/xen/drivers/passthrough/vtd/dmar.c
@@ -447,6 +447,9 @@ acpi_parse_one_drhd(struct acpi_dmar_hea
     if ( (ret = acpi_dmar_check_length(header, sizeof(*drhd))) != 0 )
         return ret;
 
+    if ( !drhd->address || !(drhd->address + 1) )
+        return -ENODEV;
+
     dmaru = xzalloc(struct acpi_drhd_unit);
     if ( !dmaru )
         return -ENOMEM;
--- a/xen/drivers/passthrough/vtd/iommu.c
+++ b/xen/drivers/passthrough/vtd/iommu.c
@@ -1159,6 +1159,9 @@ int __init iommu_alloc(struct acpi_drhd_
         dprintk(VTDPREFIX,
                 "cap = %"PRIx64" ecap = %"PRIx64"\n", iommu->cap, iommu->ecap);
     }
+    if ( !(iommu->cap + 1) || !(iommu->ecap + 1) )
+        return -ENODEV;
+
     if ( cap_fault_reg_offset(iommu->cap) +
          cap_num_fault_regs(iommu->cap) * PRIMARY_FAULT_REG_LEN >= PAGE_SIZE ||
          ecap_iotlb_offset(iommu->ecap) >= PAGE_SIZE )