{"id":"CVE-2026-80893","summary":"mm/hugetlb: fix swap entry corruption when clearing uffd-wp at fork()","details":"In the Linux kernel, the following vulnerability has been resolved:\n\nmm/hugetlb: fix swap entry corruption when clearing uffd-wp at fork()\n\ncopy_hugetlb_page_range() clears the uffd-wp bit of migration and hwpoison\nentries with huge_pte_clear_uffd_wp(), which operates on the present-PTE\nbit position.  Swap entries keep the uffd-wp state elsewhere -- the\nmigration branch reads and sets it with pte_swp_uffd_wp() and\npte_swp_mkuffd_wp() -- and the present-PTE position falls into the swap\npayload.  On x86-64 it lands in the inverted swap offset, where a\nnaturally-aligned hugetlb PFN always has the affected bit set, so the\nclear advances the encoded PFN by two pages.\n\nNo userfaultfd needs to be involved: the clear is guarded only by the\nchild VMA not being uffd-wp registered, so a plain fork() with an\nin-flight hugetlb migration entry (or a poisoned hugetlb page) corrupts\nthe entry copied into the child.  Instrumenting the clear and forking\nafter MADV_HWPOISON on a 2MB anon hugetlb page shows:\n\n  offset before=120e00\n  offset after =120e02\n\nThe fallout is mostly latent: rmap walks match migration entries by folio\nrange and remove_migration_pte() rebuilds the PTE from the folio, so a\nwithin-folio PFN skew heals once migration completes.  But any path that\nre-encodes the corrupted offset -- e.g.  hugetlb_change_protection()\nrewriting a writable migration entry via\nmake_readable_migration_entry(swp_offset(entry)) -- propagates it.\n\nMigration entries legitimately carry uffd-wp, so clear it with\npte_swp_clear_uffd_wp(), matching copy_nonpresent_pte() and\nmove_huge_pte().\n\nA hwpoison entry, on the other hand, never carries the uffd-wp bit: it is\ninstalled fresh by make_hwpoison_entry() (try_to_unmap_one() does not\npreserve uffd-wp on the hwpoison path) and hugetlb_change_protection()\nleaves hwpoison entries untouched.  There was nothing to clear there, only\nthe corruption, so drop the clear entirely.","modified":"2026-09-06T03:47:01.425693469Z","published":"2026-09-04T17:11:09.199Z","database_specific":{"cna_assigner":"Linux","osv_generated_from":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/80xxx/CVE-2026-80893.json"},"references":[{"type":"WEB","url":"https://git.kernel.org/stable/c/2b9a07002c2f296aa6a9c591213933d3492e3089"},{"type":"WEB","url":"https://git.kernel.org/stable/c/2fa11c60c9c06bafc19cf4d9efdaa36a38079e87"},{"type":"WEB","url":"https://git.kernel.org/stable/c/69cb5825d9988c7944bc9f1dc08cb233655405a7"},{"type":"WEB","url":"https://git.kernel.org/stable/c/83abe2fd5b3aeb3123b5408a5a91709c5538fb23"},{"type":"WEB","url":"https://git.kernel.org/stable/c/8b0de7005b148738d79d6c45594d566489948a68"},{"type":"WEB","url":"https://git.kernel.org/stable/c/f1b1311c0352873137768bac5a126e491271a747"},{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/80xxx/CVE-2026-80893.json"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-80893"},{"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":"bc70fbf269fdff410b0b6d75c3770b9f59117b90"},{"fixed":"f1b1311c0352873137768bac5a126e491271a747"},{"fixed":"69cb5825d9988c7944bc9f1dc08cb233655405a7"},{"fixed":"8b0de7005b148738d79d6c45594d566489948a68"},{"fixed":"2b9a07002c2f296aa6a9c591213933d3492e3089"},{"fixed":"2fa11c60c9c06bafc19cf4d9efdaa36a38079e87"},{"fixed":"83abe2fd5b3aeb3123b5408a5a91709c5538fb23"}]}],"database_specific":{"source":"https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-80893.json"}},{"package":{"name":"Kernel","ecosystem":"Linux"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"5.19.0"},{"fixed":"6.1.183"}]},{"type":"ECOSYSTEM","events":[{"introduced":"6.2.0"},{"fixed":"6.6.151"}]},{"type":"ECOSYSTEM","events":[{"introduced":"6.7.0"},{"fixed":"6.12.103"}]},{"type":"ECOSYSTEM","events":[{"introduced":"6.13.0"},{"fixed":"6.18.44"}]},{"type":"ECOSYSTEM","events":[{"introduced":"6.19.0"},{"fixed":"7.1.8"}]}],"database_specific":{"source":"https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-80893.json"}}],"schema_version":"1.9.0"}