{"schema":"threatline.record/2","record":{"id":"CVE-2026-97945","aliases":[],"summary":"x86/mm: Fix user-space data loss with MADV_FREE and THP","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 & ~_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 <-> saved-dirty transition based on the write bit,\npreserving the shadow-stack encoding rules.","categories":["Operating systems"],"product":"Linux","vendor":"Linux","ecosystem":null,"affected_ranges":[{"source":"CVE List","source_url":"https://www.cve.org/CVERecord?id=CVE-2026-97945","source_modified_at":"2026-10-19T09:11:11.655Z","fetched_at":"2026-10-23T18:45:31.882637Z","product":"Linux","vendor":"Linux","versions":[{"version":"bb3aadf7d446aaf22c725b274e2c194ac5cb2111","lessThan":"b5dec6dfb593d81fec15ba43c4fe5d58f10a49a2","status":"affected","versionType":"git"},{"version":"bb3aadf7d446aaf22c725b274e2c194ac5cb2111","lessThan":"e4d569fe2f436a9b58c048fefabf56eab68c1b7e","status":"affected","versionType":"git"},{"version":"bb3aadf7d446aaf22c725b274e2c194ac5cb2111","lessThan":"55ddbc2ca6d5db64d44c3fb8f8705b4d39eb30b7","status":"affected","versionType":"git"},{"version":"bb3aadf7d446aaf22c725b274e2c194ac5cb2111","lessThan":"a5ad97cbcfcec31430268441c10eedde73200177","status":"affected","versionType":"git"},{"version":"bb3aadf7d446aaf22c725b274e2c194ac5cb2111","lessThan":"f7491d7c81db0e7c304a7bd757a76d2fbeaff80e","status":"affected","versionType":"git"}],"defaultStatus":"unaffected"},{"source":"CVE List","source_url":"https://www.cve.org/CVERecord?id=CVE-2026-97945","source_modified_at":"2026-10-19T09:11:11.655Z","fetched_at":"2026-10-23T18:45:31.882637Z","product":"Linux","vendor":"Linux","versions":[{"version":"6.6","status":"affected"},{"version":"0","lessThan":"6.6","status":"unaffected","versionType":"semver"},{"version":"6.6.158","lessThanOrEqual":"6.6.*","status":"unaffected","versionType":"semver"},{"version":"6.12.111","lessThanOrEqual":"6.12.*","status":"unaffected","versionType":"semver"},{"version":"6.18.53","lessThanOrEqual":"6.18.*","status":"unaffected","versionType":"semver"},{"version":"7.2.7","lessThanOrEqual":"7.2.*","status":"unaffected","versionType":"semver"},{"version":"7.3","lessThanOrEqual":"*","status":"unaffected","versionType":"original_commit_for_fix"}],"defaultStatus":"affected"}],"fixed_versions":[{"source":"CVE List","source_url":"https://www.cve.org/CVERecord?id=CVE-2026-97945","source_modified_at":"2026-10-19T09:11:11.655Z","fetched_at":"2026-10-23T18:45:31.882637Z","package":{"name":"Linux","ecosystem":null},"version":"55ddbc2ca6d5db64d44c3fb8f8705b4d39eb30b7","basis":"first unaffected version stated in the CVE record"}],"cvss":null,"severity":null,"kev":{"listed":false},"epss":{"probability":0.002,"percentile":0.09338,"score_date":"2026-10-23"},"published_at":"2026-09-25T10:22:55.981Z","modified_at":"2026-10-19T09:11:11.655Z","provenance":[{"source":"CVE List","url":"https://www.cve.org/CVERecord?id=CVE-2026-97945","fetched_at":"2026-10-23T18:45:31.882637Z","source_modified_at":"2026-10-19T09:11:11.655Z"},{"source":"EPSS","url":"https://api.first.org/data/v1/epss?cve=CVE-2026-97945","fetched_at":"2026-10-23T18:42:43.628194Z","source_modified_at":"2026-10-23"}],"sources":["CVE List","EPSS"],"references":[{"source":"CVE List","url":"https://git.kernel.org/stable/c/b5dec6dfb593d81fec15ba43c4fe5d58f10a49a2"},{"source":"CVE List","url":"https://git.kernel.org/stable/c/e4d569fe2f436a9b58c048fefabf56eab68c1b7e"},{"source":"CVE List","url":"https://git.kernel.org/stable/c/55ddbc2ca6d5db64d44c3fb8f8705b4d39eb30b7"},{"source":"CVE List","url":"https://git.kernel.org/stable/c/a5ad97cbcfcec31430268441c10eedde73200177"},{"source":"CVE List","url":"https://git.kernel.org/stable/c/f7491d7c81db0e7c304a7bd757a76d2fbeaff80e"}],"locations":[],"motoko_assessment":{"status":"requires_architecture_review","automatic_remediation":false},"cve_state":"PUBLISHED","classification":{"method":"product-first software-layer rules","rules_version":"2.1","matched_on":"product","confidence":"heuristic","reviewed":false},"change_timestamp":"2026-10-19T09:11:11.655Z","content_hash":"aa61e4b64a27982692bcd3a36ab80c312166d261bcc0af1fad4ecc3ccb442cad"}}