mm/userfaultfd: fix kmap_local LIFO ordering for CONFIG_HIGHPTE

{
  "id": "cb78d5b6b4457373b6134b13876c6c04b0755f3580561da1a6f650dc96d10eb4",
  "url": "https://osv.dev/vulnerability/CVE-2025-39899",
  "method": "structured",
  "payload": {
    "kind": "advisory",
    "title": "mm/userfaultfd: fix kmap_local LIFO ordering for CONFIG_HIGHPTE",
    "summary": "In the Linux kernel, the following vulnerability has been resolved: mm/userfaultfd: fix kmap_local LIFO ordering for CONFIG_HIGHPTE With CONFIG_HIGHPTE on 32-bit ARM, move_pages_pte() maps PTE pages using kmap_local_page(), which requires unmapping in Last-In-First-Out order. The current code maps dst_pte first, then src_pte, but unmaps them in the same order (dst_pte, src_pte), violating the LIFO requirement. This causes the warning in kunmap_local_indexed(): WARNING: CPU: 0 PID: 604 at mm/highmem.c:622 kunmap_local_indexed+0x178/0x17c addr \\!= __fix_to_virt(FIX_KMAP_BEGIN + idx) Fix this by reversing the unmap order to respect LIFO ordering. This issue follows the same pattern as similar fixes: - commit eca6828403b8 (\"crypto: skcipher - fix mismatch between mapping and unmapping order\") - commit 8cf57c6df818 (\"nilfs2: eliminate staggered calls to kunmap in nilfs_rename\") Both of which addressed the same fundamental requirement that kmap_local operations must follow LIFO ordering.",
    "evidence": "osv:CVE-2025-39899",
    "products": [
      {
        "name": {
          "value": "Kernel",
          "evidence": "/affected/1/package/name"
        },
        "prerequisites": [],
        "fixed_versions": [
          {
            "value": "6.12.46",
            "evidence": "/affected/1/ranges"
          },
          {
            "value": "6.16.6",
            "evidence": "/affected/1/ranges"
          }
        ],
        "affected_versions": []
      }
    ],
    "severity": "medium",
    "structured": {
      "id": "CVE-2025-39899",
      "aliases": [
        "CVE-2025-39899"
      ],
      "metrics": [
        {
          "type": "CVSS_V3",
          "score": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H"
        }
      ],
      "affected": [
        {
          "ranges": [
            {
              "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
              "type": "GIT",
              "events": [
                {
                  "introduced": "adef440691bab824e39c1b17382322d195e1fab0"
                },
                {
                  "fixed": "b051f707018967ea8f697d790a1ed8c443f63812"
                },
                {
                  "fixed": "bd1ee62759d0bd4d6b909731c076c230ac89d61e"
                },
                {
                  "fixed": "9614d8bee66387501f48718fa306e17f2aa3f2f3"
                }
              ]
            }
          ],
          "database_specific": {
            "source": "https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2025-39899.json"
          }
        },
        {
          "ranges": [
            {
              "type": "ECOSYSTEM",
              "events": [
                {
                  "introduced": "6.8.0"
                },
                {
                  "fixed": "6.12.46"
                }
              ]
            },
            {
              "type": "ECOSYSTEM",
              "events": [
                {
                  "introduced": "6.13.0"
                },
                {
                  "fixed": "6.16.6"
                }
              ]
            }
          ],
          "package": {
            "name": "Kernel",
            "ecosystem": "Linux"
          },
          "database_specific": {
            "source": "https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2025-39899.json"
          }
        }
      ],
      "modified": "2026-10-28T02:30:23.967068046Z",
      "provider": "osv",
      "references": [
        "https://git.kernel.org/stable/c/9614d8bee66387501f48718fa306e17f2aa3f2f3",
        "https://git.kernel.org/stable/c/b051f707018967ea8f697d790a1ed8c443f63812",
        "https://git.kernel.org/stable/c/bd1ee62759d0bd4d6b909731c076c230ac89d61e",
        "https://github.com/CVEProject/cvelistV5/tree/main/cves/2025/39xxx/CVE-2025-39899.json",
        "https://nvd.nist.gov/vuln/detail/CVE-2025-39899",
        "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git"
      ],
      "provider_metadata": {
        "cna_assigner": "Linux",
        "osv_generated_from": "https://github.com/CVEProject/cvelistV5/tree/main/cves/2025/39xxx/CVE-2025-39899.json"
      }
    },
    "related_cves": [
      {
        "value": "CVE-2025-39899",
        "evidence": "/id"
      }
    ],
    "security_relevant": true,
    "severity_evidence": "/severity/0/score"
  },
  "source_id": "core-osv",
  "document_id": 490646,
  "published_at": "2025-10-01T07:42:47.1+00:00"
}