{
  "affected": [
    {
      "ranges": [
        {
          "events": [
            {
              "introduced": "bb3aadf7d446aaf22c725b274e2c194ac5cb2111"
            },
            {
              "fixed": "e4d569fe2f436a9b58c048fefabf56eab68c1b7e"
            },
            {
              "fixed": "55ddbc2ca6d5db64d44c3fb8f8705b4d39eb30b7"
            },
            {
              "fixed": "a5ad97cbcfcec31430268441c10eedde73200177"
            },
            {
              "fixed": "f7491d7c81db0e7c304a7bd757a76d2fbeaff80e"
            }
          ],
          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
          "type": "GIT"
        }
      ]
    },
    {
      "package": {
        "ecosystem": "Linux",
        "name": "Kernel"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "6.6.0"
            },
            {
              "fixed": "6.12.111"
            }
          ],
          "type": "ECOSYSTEM"
        },
        {
          "events": [
            {
              "introduced": "6.13.0"
            },
            {
              "fixed": "6.18.53"
            }
          ],
          "type": "ECOSYSTEM"
        },
        {
          "events": [
            {
              "introduced": "6.19.0"
            },
            {
              "fixed": "7.2.7"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "database_specific": {
    "cna_assigner": "Linux",
    "osv_generated_from": "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/97xxx/CVE-2026-97945.json"
  },
  "details": "In the Linux kernel, the following vulnerability has been resolved:\n\nx86/mm: Fix user-space data loss with MADV_FREE and THP\n\nSome of users of Polars (a data analytics library) have lost production\ndata from this bug. They seem to have just the right combination of\nhuge pages, MADV_FREE and heavy reclaim pressure.\n\npmd_modify() masks the old value with (_HPAGE_CHG_MASK \u0026 ~_PAGE_DIRTY),\nsilently discarding the hardware dirty bit.  The subsequent\npmd_mksaveddirty() call is supposed to transfer _PAGE_DIRTY into\n_PAGE_SAVED_DIRTY when write-protecting, but the dirty bit was already\nstripped from the value, so there is nothing left to transfer.\n\nContrast with pte_modify(), which keeps _PAGE_DIRTY_BITS in its mask,\nand pud_modify(), which keeps _HPAGE_CHG_MASK untouched: pmd_modify()\nis the odd one out.  Any pmd_modify() on a writable, dirty PMD loses\nthe dirty state.\n\nOne visible consequence is data loss with MADV_FREE on PMD-mapped THP:\n\n    memset(buf, 0x5A, size);          // PMD-mapped THP, PMD dirty\n    madvise(buf, size, MADV_FREE);    // PMD cleaned but left writable,\n                                      // folio marked lazyfree\n    memset(buf, 0x5A, size);          // hardware sets _PAGE_DIRTY again\n    mprotect(buf, size, PROT_READ);   // pmd_modify() drops the dirty bit\n    mprotect(buf, size, PROT_READ|PROT_WRITE);\n    // ... memory pressure ...\n\nReclaim (e.g. under memcg pressure) then finds the lazyfree folio with\nno dirty bit set anywhere and frees it in\n__discard_anon_folio_pmd_locked(), even though the data was rewritten\nafter MADV_FREE; subsequent reads fault in fresh zero pages.  NUMA\nhinting alone can trigger the same loss, as do_huge_pmd_numa_page()\nrestores the PMD through pmd_modify() as well.\n\nPMD-mapped file THPs are affected too: mprotect()/NUMA hinting dropping\nthe dirty bit means rewritten data is never written back.\n\nFix it by keeping _PAGE_DIRTY in the preserved mask, exactly like\npte_modify() and pud_modify() do.  The existing\npmd_mksaveddirty()/pmd_clear_saveddirty() pair then performs the\nhardware-dirty \u003c-\u003e saved-dirty transition based on the write bit,\npreserving the shadow-stack encoding rules.",
  "id": "CVE-2026-97945",
  "modified": "2026-09-27T03:30:44.473380377Z",
  "published": "2026-09-25T10:22:55.981Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/55ddbc2ca6d5db64d44c3fb8f8705b4d39eb30b7"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/a5ad97cbcfcec31430268441c10eedde73200177"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/e4d569fe2f436a9b58c048fefabf56eab68c1b7e"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/f7491d7c81db0e7c304a7bd757a76d2fbeaff80e"
    },
    {
      "type": "ADVISORY",
      "url": "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/97xxx/CVE-2026-97945.json"
    },
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-97945"
    },
    {
      "type": "PACKAGE",
      "url": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git"
    }
  ],
  "schema_version": "1.9.0",
  "summary": "x86/mm: Fix user-space data loss with MADV_FREE and THP"
}