{"id":"CVE-2026-93066","summary":"x86/mm/pat: Take cpa_lock around large-page collapse","details":"In the Linux kernel, the following vulnerability has been resolved:\n\nx86/mm/pat: Take cpa_lock around large-page collapse\n\nLoading and unloading modules concurrently on several CPUs on a KASAN\nbuild, with a short delay injected at the CPA page-table lookup to\nwiden the window, faults within minutes:\n\n  BUG: KASAN: use-after-free in __change_page_attr+0x7cc/0x7e0\n  Write of size 8 at addr ffff888181139718 by task modprobe\n  ...\n  The buggy address belongs to the physical page:\n   pfn:0x181139 ... page_type: f2(table)\n\ncpa_collapse_large_pages() rebuilds a leaf PMD from its 4K PTEs and\nfrees the old PTE-table pages, while __change_page_attr() fetches a\nPTE pointer from a lockless lookup_address_in_pgd_attr() and writes\nit with set_pte_atomic() only later. When module text is served from\na shared large ROX mapping the two run on the same PMD:\n\n  CPU A (module load)              CPU B (module finalize)\n  -------------------              -----------------------\n  execmem_make_temp_rw\n   set_memory_nx\n    __change_page_attr\n     split 2M -\u003e 4K table P\n     kpte = &P[i]  (lockless)\n                                   execmem_restore_rox\n                                    set_memory_rox (CPA_COLLAPSE)\n                                     cpa_collapse_large_pages\n                                      rebuild leaf PMD\n                                      flush_tlb_all\n                                      pagetable_free(P)\n     set_pte_atomic(kpte, ...)\n       -\u003e writes into freed P\n\nP is a page-table page (page_type: table), reused at once, so the\nwrite corrupts whatever got the page next: a bad-pte or bad-page\nsplat, or a fatal fault once P has been turned into read-only text.\n\nThe flush_tlb_all() before the free does not close this: its IPI only\nserializes against page-table walkers that run with interrupts off\n(e.g. GUP-fast); the walk in __change_page_attr() runs with interrupts\non, so nothing stops it from holding a stale pointer into P.\n\nSerialize the collapse - the PMD rebuild, TLB flush and PTE-table\nfree - under cpa_lock, the same lock __change_page_attr() now takes\nunconditionally since commit (\"x86/mm/pat: stop gating cpa_lock on\ndebug_pagealloc_enabled()\"), so a concurrent walker can no longer\nhold a pointer into a table the collapse is about to free.","modified":"2026-09-19T03:47:30.977665073Z","published":"2026-09-17T16:10:51.612Z","database_specific":{"osv_generated_from":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/93xxx/CVE-2026-93066.json","cna_assigner":"Linux"},"references":[{"type":"WEB","url":"https://git.kernel.org/stable/c/1aac65f3e651334259ecb2a5f5ddb81c01f02599"},{"type":"WEB","url":"https://git.kernel.org/stable/c/591b6fac9df3f43522e8ff6eed8662f8b6f1a124"},{"type":"WEB","url":"https://git.kernel.org/stable/c/fb97d1d6c20692e15247fa5c8b894b2325e38aee"},{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/93xxx/CVE-2026-93066.json"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-93066"},{"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":"41d88484c71cd4f659348da41b7b5b3dbd3be1f6"},{"fixed":"591b6fac9df3f43522e8ff6eed8662f8b6f1a124"},{"fixed":"fb97d1d6c20692e15247fa5c8b894b2325e38aee"},{"fixed":"1aac65f3e651334259ecb2a5f5ddb81c01f02599"}]}],"database_specific":{"source":"https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-93066.json"}},{"package":{"name":"Kernel","ecosystem":"Linux"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"6.15.0"},{"fixed":"6.18.52"}]},{"type":"ECOSYSTEM","events":[{"introduced":"6.19.0"},{"fixed":"7.2.6"}]}],"database_specific":{"source":"https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-93066.json"}}],"schema_version":"1.9.0"}