x86/mm/pat: fix VM_PAT handling in COW mappings

{
  "id": "73fe4ac2995274bbf2de556dc469e1365320a97f9286ac134044f30fe2b6b2cd",
  "url": "https://osv.dev/vulnerability/CVE-2024-35877",
  "method": "structured",
  "payload": {
    "kind": "advisory",
    "title": "x86/mm/pat: fix VM_PAT handling in COW mappings",
    "summary": "In the Linux kernel, the following vulnerability has been resolved: x86/mm/pat: fix VM_PAT handling in COW mappings PAT handling won't do the right thing in COW mappings: the first PTE (or, in fact, all PTEs) can be replaced during write faults to point at anon folios. Reliably recovering the correct PFN and cachemode using follow_phys() from PTEs will not work in COW mappings. Using follow_phys(), we might just get the address+protection of the anon folio (which is very wrong), or fail on swap/nonswap entries, failing follow_phys() and triggering a WARN_ON_ONCE() in untrack_pfn() and track_pfn_copy(), not properly calling free_pfn_range(). In free_pfn_range(), we either wouldn't call memtype_free() or would call it with the wrong range, possibly leaking memory. To fix that, let's update follow_phys() to refuse returning anon folios, and fallback to using the stored PFN inside vma->vm_pgoff for COW mappings if we run into that. We will now properly handle untrack_pfn() with COW mappings, where we don't need the cachemode. We'll have to fail fork()->track_pfn_copy() if the first page was replaced by an anon folio, though: we'd have to store the cachemode in the VMA to make this work, likely growing the VMA size. For now, lets keep it simple and let track_pfn_copy() just fail in that case: it would have failed in the past with swap/nonswap entries already, and it would have done the wrong thing with anon folios. Simple reproducer to trigger the WARN_ON_ONCE() in untrack_pfn(): ",
    "evidence": "osv:CVE-2024-35877",
    "products": [
      {
        "name": {
          "value": "Kernel",
          "evidence": "/affected/1/package/name"
        },
        "prerequisites": [],
        "fixed_versions": [
          {
            "value": "4.19.312",
            "evidence": "/affected/1/ranges"
          },
          {
            "value": "5.4.274",
            "evidence": "/affected/1/ranges"
          },
          {
            "value": "5.10.215",
            "evidence": "/affected/1/ranges"
          },
          {
            "value": "5.15.155",
            "evidence": "/affected/1/ranges"
          },
          {
            "value": "6.1.85",
            "evidence": "/affected/1/ranges"
          },
          {
            "value": "6.6.26",
            "evidence": "/affected/1/ranges"
          },
          {
            "value": "6.8.5",
            "evidence": "/affected/1/ranges"
          }
        ],
        "affected_versions": []
      }
    ],
    "severity": "unknown",
    "structured": {
      "id": "CVE-2024-35877",
      "aliases": [
        "CVE-2024-35877"
      ],
      "affected": [
        {
          "ranges": [
            {
              "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
              "type": "GIT",
              "events": [
                {
                  "introduced": "5899329b19100c0b82dc78e9b21ed8b920c9ffb3"
                },
                {
                  "fixed": "f18681daaec9665a15c5e7e0f591aad5d0ac622b"
                },
                {
                  "fixed": "09e6bb53217bf388a0d2fd7fb21e74ab9dffc173"
                },
                {
                  "fixed": "c2b2430b48f3c9eaccd2c3d2ad75bb540d4952f4"
                },
                {
                  "fixed": "7cfee26d1950250b14c5cb0a37b142f3fcc6396a"
                },
                {
                  "fixed": "97e93367e82752e475a33839a80b33bdbef1209f"
                },
                {
                  "fixed": "51b7841f3fe84606ec0bd8da859d22e05e5419ec"
                },
                {
                  "fixed": "1341e4b32e1fb1b0acd002ccd56f07bd32f2abc6"
                },
                {
                  "fixed": "04c35ab3bdae7fefbd7c7a7355f29fa03a035221"
                }
              ]
            }
          ],
          "database_specific": {
            "source": "https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2024-35877.json"
          }
        },
        {
          "ranges": [
            {
              "type": "ECOSYSTEM",
              "events": [
                {
                  "introduced": "2.6.29"
                },
                {
                  "fixed": "4.19.312"
                }
              ]
            },
            {
              "type": "ECOSYSTEM",
              "events": [
                {
                  "introduced": "4.20.0"
                },
                {
                  "fixed": "5.4.274"
                }
              ]
            },
            {
              "type": "ECOSYSTEM",
              "events": [
                {
                  "introduced": "5.5.0"
                },
                {
                  "fixed": "5.10.215"
                }
              ]
            },
            {
              "type": "ECOSYSTEM",
              "events": [
                {
                  "introduced": "5.11.0"
                },
                {
                  "fixed": "5.15.155"
                }
              ]
            },
            {
              "type": "ECOSYSTEM",
              "events": [
                {
                  "introduced": "5.16.0"
                },
                {
                  "fixed": "6.1.85"
                }
              ]
            },
            {
              "type": "ECOSYSTEM",
              "events": [
                {
                  "introduced": "6.2.0"
                },
                {
                  "fixed": "6.6.26"
                }
              ]
            },
            {
              "type": "ECOSYSTEM",
              "events": [
                {
                  "introduced": "6.7.0"
                },
                {
                  "fixed": "6.8.5"
                }
              ]
            }
          ],
          "package": {
            "name": "Kernel",
            "ecosystem": "Linux"
          },
          "database_specific": {
            "source": "https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2024-35877.json"
          }
        }
      ],
      "modified": "2026-10-28T02:30:23.523832283Z",
      "provider": "osv",
      "references": [
        "https://cert-portal.siemens.com/productcert/html/ssa-265688.html",
        "https://git.kernel.org/stable/c/04c35ab3bdae7fefbd7c7a7355f29fa03a035221",
        "https://git.kernel.org/stable/c/09e6bb53217bf388a0d2fd7fb21e74ab9dffc173",
        "https://git.kernel.org/stable/c/1341e4b32e1fb1b0acd002ccd56f07bd32f2abc6",
        "https://git.kernel.org/stable/c/51b7841f3fe84606ec0bd8da859d22e05e5419ec",
        "https://git.kernel.org/stable/c/7cfee26d1950250b14c5cb0a37b142f3fcc6396a",
        "https://git.kernel.org/stable/c/97e93367e82752e475a33839a80b33bdbef1209f",
        "https://git.kernel.org/stable/c/c2b2430b48f3c9eaccd2c3d2ad75bb540d4952f4",
        "https://git.kernel.org/stable/c/f18681daaec9665a15c5e7e0f591aad5d0ac622b",
        "https://lists.debian.org/debian-lts-announce/2024/06/msg00017.html",
        "https://lists.debian.org/debian-lts-announce/2024/06/msg00020.html",
        "https://github.com/CVEProject/cvelistV5/tree/main/cves/2024/35xxx/CVE-2024-35877.json",
        "https://nvd.nist.gov/vuln/detail/CVE-2024-35877",
        "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/2024/35xxx/CVE-2024-35877.json"
      }
    },
    "related_cves": [
      {
        "value": "CVE-2024-35877",
        "evidence": "/id"
      }
    ],
    "security_relevant": true,
    "severity_evidence": null
  },
  "source_id": "core-osv",
  "document_id": 489837,
  "published_at": "2024-05-19T08:34:34.604+00:00"
}