CVE-2025-39961 iommu/amd/pgtbl: Fix possible race while increase page table level
A race condition in the AMD IOMMU driver can cause unmap operations to fail, potentially leading to denial of service.
- Exploited in the wild
- Not known
- Login needed
- Any signed-in user
- Attackable
- Local or same network only
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2025-39961?
CVE-2025-39961 is a high-severity vulnerability in Linux kernel, published on 9 Oct 2025. It can only be exploited from the same machine or local network, with no action from the victim.
Official description
In the Linux kernel, the following vulnerability has been resolved:
iommu/amd/pgtbl: Fix possible race while increase page table level
The AMD IOMMU host page table implementation supports dynamic page table levels (up to 6 levels), starting with a 3-level configuration that expands based on IOVA address. The kernel maintains a root pointer and current page table level to enable proper page table walks in alloc_pte()/fetch_pte() operations.
The IOMMU IOVA allocator initially starts with 32-bit address and onces its exhuasted it switches to 64-bit address (max address is determined based on IOMMU and device DMA capability). To support larger IOVA, AMD IOMMU driver increases page table level.
But in unmap path (iommu_v1_unmap_pages()), fetch_pte() reads pgtable->[root/mode] without lock. So its possible that in exteme corner case, when increase_address_space() is updating pgtable->[root/mode], fetch_pte() reads wrong page table level (pgtable->mode). It does compare the value with level encoded in page table and returns NULL. This will result is iommu_unmap ops to fail and upper layer may retry/log WARN_ON.
CPU 0 CPU 1 ------ ------ map pages unmap pages alloc_pte() -> increase_address_space() iommu_v1_unmap_pages() -> fetch_pte() pgtable->root = pte (new root value) READ pgtable->[mode/root] Reads new root, old mode Updates mode (pgtable->mode += 1)
Since Page table level updates are infrequent and already synchronized with a spinlock, implement seqcount to enable lock-free read operations on the read path.
Weakness: CWE-362
Which versions are affected by CVE-2025-39961?
It affects 1 product.
Products include Linux kernel.
How do I fix CVE-2025-39961?
Apply the vendor's patch.
Is CVE-2025-39961 being exploited?
There is no known exploitation of CVE-2025-39961 in the wild and no public exploit code.
Other vulnerabilities in Linux kernel
Sources
Also known as AZL-68348, AZL-76434, BELL-CVE-2025-39961, DEBIAN-CVE-2025-39961, GHSA-cq2w-q6m3-mhw9, ROOT-OS-DEBIAN-11-CVE-2025-39961 and 5 more.