{"id":"CVE-2026-64181","summary":"mm: fix __vm_normal_page() to handle missing support for pmd_special()/pud_special()","details":"In the Linux kernel, the following vulnerability has been resolved:\n\nmm: fix __vm_normal_page() to handle missing support for pmd_special()/pud_special()\n\nOn x86 32-bit with THP enabled, zap_huge_pmd() is seen to generate a\n\"WARNING: mm/memory.c:735 at __vm_normal_page+0x6a/0x7d\", from the\nVM_WARN_ON_ONCE(is_zero_pfn(pfn) || is_huge_zero_pfn(pfn)); followed by\n\"BUG: Bad rss-counter state\"s, then later \"BUG: Bad page state\"s when\nreclaim gets to call shrink_huge_zero_folio_scan().\n\nIt's as if the _PAGE_SPECIAL bit never got set in the huge_zero pmd: and\nindeed, whereas pte_special() and pte_mkspecial() are subject to a\ndedicated CONFIG_ARCH_HAS_PTE_SPECIAL, pmd_special() and pmd_mkspecial()\nare subject to CONFIG_ARCH_SUPPORTS_PMD_PFNMAP, which is never enabled on\nany 32-bit architecture.\n\nWhile the problem was exposed through commit d80a9cb1a64a\n(\"mm/huge_memory: add and use normal_or_softleaf_folio_pmd()\"), it was an\noversight in commit af38538801c6 (\"mm/memory: factor out common code from\nvm_normal_page_*()\") and would result in other problems:\n* huge zero folio accounted in smaps, pagemap (PAGE_IS_FILE) and\n  numamaps as file-backed THP\n* folio_walk_start() returning the folio even without FW_ZEROPAGE set.\n  Callers seem to tolerate that, though.\n\n... and triggering the VM_WARN_ON_ONE(), although never reported so far.\n\nTo fix it, teach vm_normal_page_pmd()/vm_normal_page_pud() to consider\nwhether pmd_special/pud_special is actually implemented.","modified":"2026-07-22T05:30:04.913522838Z","published":"2026-07-19T15:41:04.455Z","database_specific":{"osv_generated_from":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/64xxx/CVE-2026-64181.json","cna_assigner":"Linux"},"references":[{"type":"WEB","url":"https://git.kernel.org/stable/c/62153767e8fc3889bc6508e9ffe927aaf64c4334"},{"type":"WEB","url":"https://git.kernel.org/stable/c/9052ea2ee2233be5d4786b8909151ca2bfbedf99"},{"type":"WEB","url":"https://git.kernel.org/stable/c/c0c6ccd9828c3a1950623b546fa57292a77b5c73"},{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/64xxx/CVE-2026-64181.json"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-64181"},{"type":"PACKAGE","url":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git"}],"affected":[{"ranges":[{"type":"GIT","repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","events":[{"introduced":"af38538801c6a97565b44700ee6695d7d60ad779"},{"fixed":"62153767e8fc3889bc6508e9ffe927aaf64c4334"},{"fixed":"9052ea2ee2233be5d4786b8909151ca2bfbedf99"},{"fixed":"c0c6ccd9828c3a1950623b546fa57292a77b5c73"}]}],"database_specific":{"source":"https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-64181.json"}},{"package":{"name":"Kernel","ecosystem":"Linux"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"6.18.0"},{"fixed":"6.18.34"}]},{"type":"ECOSYSTEM","events":[{"introduced":"6.19.0"},{"fixed":"7.0.11"}]}],"database_specific":{"source":"https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-64181.json"}}],"schema_version":"1.7.5","severity":[{"type":"CVSS_V3","score":"CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H"}]}