{"id":"CVE-2026-97945","revision":"a5967b9b608e4011b98c0287a5722409","records":[{"revision":"a5967b9b608e4011b98c0287a5722409","observedAt":"2026-10-23T15:48:27.903+00:00","statement":{"source":"cve-program","id":"CVE-2026-97945","aliases":[],"title":"x86/mm: Fix user-space data loss with MADV_FREE and THP","description":"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.","state":0,"publishedAt":"2026-09-25T10:22:55.981+00:00","modifiedAt":"2026-10-19T09:11:11.655+00:00","affected":[{"ecosystem":"Vendor product","name":"Linux","ranges":[],"versions":[],"rawVersionEvidence":"{\n                    \"product\": \"Linux\",\n                    \"vendor\": \"Linux\",\n                    \"defaultStatus\": \"unaffected\",\n                    \"repo\": \"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git\",\n                    \"programFiles\": [\n                        \"arch/x86/include/asm/pgtable.h\"\n                    ],\n                    \"versions\": [\n                        {\n                            \"version\": \"bb3aadf7d446aaf22c725b274e2c194ac5cb2111\",\n                            \"lessThan\": \"b5dec6dfb593d81fec15ba43c4fe5d58f10a49a2\",\n                            \"status\": \"affected\",\n                            \"versionType\": \"git\"\n                        },\n                        {\n                            \"version\": \"bb3aadf7d446aaf22c725b274e2c194ac5cb2111\",\n                            \"lessThan\": \"e4d569fe2f436a9b58c048fefabf56eab68c1b7e\",\n                            \"status\": \"affected\",\n                            \"versionType\": \"git\"\n                        },\n                        {\n                            \"version\": \"bb3aadf7d446aaf22c725b274e2c194ac5cb2111\",\n                            \"lessThan\": \"55ddbc2ca6d5db64d44c3fb8f8705b4d39eb30b7\",\n                            \"status\": \"affected\",\n                            \"versionType\": \"git\"\n                        },\n                        {\n                            \"version\": \"bb3aadf7d446aaf22c725b274e2c194ac5cb2111\",\n                            \"lessThan\": \"a5ad97cbcfcec31430268441c10eedde73200177\",\n                            \"status\": \"affected\",\n                            \"versionType\": \"git\"\n                        },\n                        {\n                            \"version\": \"bb3aadf7d446aaf22c725b274e2c194ac5cb2111\",\n                            \"lessThan\": \"f7491d7c81db0e7c304a7bd757a76d2fbeaff80e\",\n                            \"status\": \"affected\",\n                            \"versionType\": \"git\"\n                        }\n                    ]\n                }"},{"ecosystem":"Vendor product","name":"Linux","ranges":[],"versions":[],"rawVersionEvidence":"{\n                    \"product\": \"Linux\",\n                    \"vendor\": \"Linux\",\n                    \"defaultStatus\": \"affected\",\n                    \"repo\": \"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git\",\n                    \"programFiles\": [\n                        \"arch/x86/include/asm/pgtable.h\"\n                    ],\n                    \"versions\": [\n                        {\n                            \"version\": \"6.6\",\n                            \"status\": \"affected\"\n                        },\n                        {\n                            \"version\": \"0\",\n                            \"lessThan\": \"6.6\",\n                            \"status\": \"unaffected\",\n                            \"versionType\": \"semver\"\n                        },\n                        {\n                            \"version\": \"6.6.158\",\n                            \"lessThanOrEqual\": \"6.6.*\",\n                            \"status\": \"unaffected\",\n                            \"versionType\": \"semver\"\n                        },\n                        {\n                            \"version\": \"6.12.111\",\n                            \"lessThanOrEqual\": \"6.12.*\",\n                            \"status\": \"unaffected\",\n                            \"versionType\": \"semver\"\n                        },\n                        {\n                            \"version\": \"6.18.53\",\n                            \"lessThanOrEqual\": \"6.18.*\",\n                            \"status\": \"unaffected\",\n                            \"versionType\": \"semver\"\n                        },\n                        {\n                            \"version\": \"7.2.7\",\n                            \"lessThanOrEqual\": \"7.2.*\",\n                            \"status\": \"unaffected\",\n                            \"versionType\": \"semver\"\n                        },\n                        {\n                            \"version\": \"7.3\",\n                            \"lessThanOrEqual\": \"*\",\n                            \"status\": \"unaffected\",\n                            \"versionType\": \"original_commit_for_fix\"\n                        }\n                    ]\n                }"}],"metrics":[],"references":["https://git.kernel.org/stable/c/b5dec6dfb593d81fec15ba43c4fe5d58f10a49a2","https://git.kernel.org/stable/c/e4d569fe2f436a9b58c048fefabf56eab68c1b7e","https://git.kernel.org/stable/c/55ddbc2ca6d5db64d44c3fb8f8705b4d39eb30b7","https://git.kernel.org/stable/c/a5ad97cbcfcec31430268441c10eedde73200177","https://git.kernel.org/stable/c/f7491d7c81db0e7c304a7bd757a76d2fbeaff80e"],"sourceUrl":"https://www.cve.org/CVERecord?id=CVE-2026-97945","license":"CVE Program Terms of Use","key":"cve-program:CVE-2026-97945","identifiers":["CVE-2026-97945"]},"retained":false,"historicalAffected":[]}],"coverage":[]}