In the Linux kernel, the following vulnerability has been resolved:
iommu/amd: Fix ineffective error check in nested domain allocation
amd_iommu_pdom_id_alloc() returns an int: a domain ID on success, or the
negative errno from ida_alloc_range() when the ID space is exhausted or
memory is short. amd_iommu_alloc_domain_nested() stores that return value
in gdom_info->hdom_id, which is a u32, and only then tests it:
<pre>
gdom_info->hdom_id = amd_iommu_pdom_id_alloc();
if (gdom_info->hdom_id <= 0) {
</pre>
The assignment discards the sign, so -ENOSPC becomes 0xffffffe4 and the
test never fires. The nested domain is then set up with a host domain ID
that was never allocated, instead of the allocation failing with -ENOSPC.
Keep the value in an int, test it there, and store it only once it is
known to be valid, which is what the other amd_iommu_pdom_id_alloc()
callers already do.
CVSS Vector: CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:C/C:H/I:H/A:H
CVSS Score: 7.8
AV:L - The patched function amd_iommu_alloc_domain_nested() is reached only via the IOMMU_HWPT_ALLOC ioctl on a local iommufd fd (/dev/iommu) against an AMD vIOMMU (iommufd_hwpt_alloc -> viommu->ops->alloc_domain_nested); no remote protocol carries the input.
AC:H - The failure path needs ida_alloc_range() in amd_iommu_pdom_id_alloc() to fail: either all 65535 global host domain IDs are in use with a victim domain holding 0xffe4, which lowest-first allocation doesn't let the attacker arrange on demand, or a GFP_ATOMIC failure the attacker cannot force.
PR:L - Needs a VMM-style user that has been given /dev/iommu (0660) and a bound VFIO device cdev to create a vIOMMU and nested HWPTs; that is delegated device access, not full init-namespace root.
UI:N - The attacker allocates the nested HWPTs and attaches the device themselves; nobody else has to do anything.
S:C - The unallocated hdom_id (truncated to 0xffe4/0xfff4 by DTE_DOMID_MASK) is written into the DTE by set_dte_nested(), so the nested device shares IOTLB tags with another IOMMU domain, breaking the DMA isolation boundary between domains.
C:H - Because the DomID is aliased, the device's DMA can hit IOTLB translations cached for the other domain and read memory belonging to that domain.
I:H - The same aliased IOTLB entries let the device's DMA writes land in the other domain's pages, corrupting memory outside the nested domain.
A:H - Stray DMA writes into another domain's memory, plus invalidations for the parent S2 hitting the shared hdom_id, can corrupt host or guest memory used by other devices and bring them down.
| Attack Vector |
Local |
Scope |
Changed |
| Attack Complexity |
High |
Confidentiality Impact |
High |
| Privileges Required |
Low |
Integrity Impact |
High |
| User Interaction |
None |
Availability Impact |
High |
AV:L - The patched function amd_iommu_alloc_domain_nested() is reached only via the IOMMU_HWPT_ALLOC ioctl on a local iommufd fd (/dev/iommu) against an AMD vIOMMU (iommufd_hwpt_alloc -> viommu->ops->alloc_domain_nested); no remote protocol carries the input.
AC:H - The failure path needs ida_alloc_range() in amd_iommu_pdom_id_alloc() to fail: either all 65535 global host domain IDs are in use with a victim domain holding 0xffe4, which lowest-first allocation doesn't let the attacker arrange on demand, or a GFP_ATOMIC failure the attacker cannot force.
PR:L - Needs a VMM-style user that has been given /dev/iommu (0660) and a bound VFIO device cdev to create a vIOMMU and nested HWPTs; that is delegated device access, not full init-namespace root.
UI:N - The attacker allocates the nested HWPTs and attaches the device themselves; nobody else has to do anything.
S:C - The unallocated hdom_id (truncated to 0xffe4/0xfff4 by DTE_DOMID_MASK) is written into the DTE by set_dte_nested(), so the nested device shares IOTLB tags with another IOMMU domain, breaking the DMA isolation boundary between domains.
C:H - Because the DomID is aliased, the device's DMA can hit IOTLB translations cached for the other domain and read memory belonging to that domain.
I:H - The same aliased IOTLB entries let the device's DMA writes land in the other domain's pages, corrupting memory outside the nested domain.
A:H - Stray DMA writes into another domain's memory, plus invalidations for the parent S2 hitting the shared hdom_id, can corrupt host or guest memory used by other devices and bring them down.
CVSS 3.1