[xen stable-4.16] VT-d: refuse to use IOMMU with reserved CAP.ND value

[patchbot@xxxxxxx]

commit b378ee56c7e0bb5eeb35dcc55b3d29e5f50eb566
Author:     Jan Beulich <jbeulich@xxxxxxxx>
AuthorDate: Tue Jun 7 13:58:16 2022 +0200
Commit:     Jan Beulich <jbeulich@xxxxxxxx>
CommitDate: Tue Jun 7 13:58:16 2022 +0200

    VT-d: refuse to use IOMMU with reserved CAP.ND value
    
    The field taking the value 7 (resulting in 18-bit DIDs when using the
    calculation in cap_ndoms(), when the DID fields are only 16 bits wide)
    is reserved. Instead of misbehaving in case we would encounter such an
    IOMMU, refuse to use it.
    
    Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
    Reviewed-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>
    Reviewed-by: Kevin Tian <kevin.tian@xxxxxxxxx>
    master commit: a1545fbf45c689aff39ce76a6eaa609d32ef72a7
    master date: 2022-04-20 10:54:26 +0200
---
 xen/drivers/passthrough/vtd/iommu.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/xen/drivers/passthrough/vtd/iommu.c 
b/xen/drivers/passthrough/vtd/iommu.c
index 93dd8aa643..8975c1de61 100644
--- a/xen/drivers/passthrough/vtd/iommu.c
+++ b/xen/drivers/passthrough/vtd/iommu.c
@@ -1279,8 +1279,11 @@ int __init iommu_alloc(struct acpi_drhd_unit *drhd)
 
     quirk_iommu_caps(iommu);
 
+    nr_dom = cap_ndoms(iommu->cap);
+
     if ( cap_fault_reg_offset(iommu->cap) +
          cap_num_fault_regs(iommu->cap) * PRIMARY_FAULT_REG_LEN >= PAGE_SIZE ||
+         ((nr_dom - 1) >> 16) /* I.e. cap.nd > 6 */ ||
          ecap_iotlb_offset(iommu->ecap) >= PAGE_SIZE )
     {
         printk(XENLOG_ERR VTDPREFIX "IOMMU: unsupported\n");
@@ -1305,7 +1308,6 @@ int __init iommu_alloc(struct acpi_drhd_unit *drhd)
         vtd_ops.sync_cache = sync_cache;
 
     /* allocate domain id bitmap */
-    nr_dom = cap_ndoms(iommu->cap);
     iommu->domid_bitmap = xzalloc_array(unsigned long, BITS_TO_LONGS(nr_dom));
     if ( !iommu->domid_bitmap )
         return -ENOMEM;
--
generated by git-patchbot for /home/xen/git/xen.git#stable-4.16