{ "dataType": "CVE_RECORD", "dataVersion": "5.2", "cveMetadata": { "cveId": "CVE-2026-97945", "assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "state": "PUBLISHED", "assignerShortName": "Linux", "dateReserved": "2026-09-25T10:18:58.204Z", "datePublished": "2026-09-25T10:22:55.981Z", "dateUpdated": "2026-10-19T09:11:11.655Z" }, "containers": { "cna": { "providerMetadata": { "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "shortName": "Linux", "dateUpdated": "2026-10-19T09:11:11.655Z" }, "descriptions": [ { "lang": "en", "value": "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." } ], "affected": [ { "product": "Linux", "vendor": "Linux", "defaultStatus": "unaffected", "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git", "programFiles": [ "arch/x86/include/asm/pgtable.h" ], "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" } ] }, { "product": "Linux", "vendor": "Linux", "defaultStatus": "affected", "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git", "programFiles": [ "arch/x86/include/asm/pgtable.h" ], "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" } ] } ], "cpeApplicability": [ { "nodes": [ { "operator": "OR", "negate": false, "cpeMatch": [ { "vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "6.6", "versionEndExcluding": "6.6.158" }, { "vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "6.6", "versionEndExcluding": "6.12.111" }, { "vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "6.6", "versionEndExcluding": "6.18.53" }, { "vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "6.6", "versionEndExcluding": "7.2.7" }, { "vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "6.6", "versionEndExcluding": "7.3" } ] } ] } ], "references": [ { "url": "https://git.kernel.org/stable/c/b5dec6dfb593d81fec15ba43c4fe5d58f10a49a2" }, { "url": "https://git.kernel.org/stable/c/e4d569fe2f436a9b58c048fefabf56eab68c1b7e" }, { "url": "https://git.kernel.org/stable/c/55ddbc2ca6d5db64d44c3fb8f8705b4d39eb30b7" }, { "url": "https://git.kernel.org/stable/c/a5ad97cbcfcec31430268441c10eedde73200177" }, { "url": "https://git.kernel.org/stable/c/f7491d7c81db0e7c304a7bd757a76d2fbeaff80e" } ], "title": "x86/mm: Fix user-space data loss with MADV_FREE and THP", "x_generator": { "engine": "bippy-1.2.0" } } } }