---
id: CVE-2025-39961
title: 'iommu/amd/pgtbl: Fix possible race while increase page table level'
summary: >-
  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), st…
severity: high
cvss: 8.8
cvssVector: 'CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:H'
cvssSource: cna
vendor: Linux
product: Linux
affected:
  - >-
    Linux >= 754265bcab78a9014f0f99cd35e0d610fcd7dfa7 <
    075abf0b1a958acfbea2435003d228e738e90346
  - >-
    Linux >= 754265bcab78a9014f0f99cd35e0d610fcd7dfa7 <
    cd92c8ab336c3a633d46e6f35ebcd3509ae7db3b
  - >-
    Linux >= 754265bcab78a9014f0f99cd35e0d610fcd7dfa7 <
    7d462bdecb7d9c32934dab44aaeb7ea7d73a27a2
  - >-
    Linux >= 754265bcab78a9014f0f99cd35e0d610fcd7dfa7 <
    1e56310b40fd2e7e0b9493da9ff488af145bdd0c
  - Linux 6fb92f18555a7b8e085267d513612dc0ff9a5360
  - Linux b15bf74405faa1a65025eb8a6eb337e140e5250a
  - Linux 0d50f7b1e8c80a8c20db5049e269468c059b0378
  - Linux 785ca708a908b9c596ede852470ba28b8dc3e40b
  - Linux >= 4.9.194 < 4.10
  - Linux >= 4.14.146 < 4.15
  - Linux >= 4.19.75 < 4.20
  - Linux >= 5.2.17 < 5.3
  - Linux 5.3
ssvc:
  exploitation: none
  automatable: 'no'
  technicalImpact: total
  timestamp: '2026-10-15T21:55:10.295299Z'
published: '2025-10-09'
updated: '2026-10-15'
sourceUpdated: '2026-10-15T22:02:34.065Z'
source: CVEORG
sourceUrl: 'https://www.cve.org/CVERecord?id=CVE-2025-39961'
references:
  - url: 'https://git.kernel.org/stable/c/075abf0b1a958acfbea2435003d228e738e90346'
  - url: 'https://git.kernel.org/stable/c/cd92c8ab336c3a633d46e6f35ebcd3509ae7db3b'
  - url: 'https://git.kernel.org/stable/c/7d462bdecb7d9c32934dab44aaeb7ea7d73a27a2'
  - url: 'https://git.kernel.org/stable/c/1e56310b40fd2e7e0b9493da9ff488af145bdd0c'
tags:
  - cve.org
epss: 0.00118
epssPercentile: 0.0171
ingestedAt: '2026-10-15T22:48:25.532Z'
---

## Overview

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.

## Affected

- `Linux >= 754265bcab78a9014f0f99cd35e0d610fcd7dfa7 < 075abf0b1a958acfbea2435003d228e738e90346`
- `Linux >= 754265bcab78a9014f0f99cd35e0d610fcd7dfa7 < cd92c8ab336c3a633d46e6f35ebcd3509ae7db3b`
- `Linux >= 754265bcab78a9014f0f99cd35e0d610fcd7dfa7 < 7d462bdecb7d9c32934dab44aaeb7ea7d73a27a2`
- `Linux >= 754265bcab78a9014f0f99cd35e0d610fcd7dfa7 < 1e56310b40fd2e7e0b9493da9ff488af145bdd0c`
- `Linux 6fb92f18555a7b8e085267d513612dc0ff9a5360`
- `Linux b15bf74405faa1a65025eb8a6eb337e140e5250a`
- `Linux 0d50f7b1e8c80a8c20db5049e269468c059b0378`
- `Linux 785ca708a908b9c596ede852470ba28b8dc3e40b`
- `Linux >= 4.9.194 < 4.10`
- `Linux >= 4.14.146 < 4.15`
- `Linux >= 4.19.75 < 4.20`
- `Linux >= 5.2.17 < 5.3`
- `Linux 5.3`

## Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.