mm: fix __vm_normal_page() to handle missing support for pmd_special()/pud_special()

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Summary

CVECVE-2026-64181
StatePUBLISHED
AssignerLinux
Source PriorityCVE Program / NVD first with legacy fallback
Published2026-07-19 16:18:00 UTC
Updated2026-07-19 16:18:00 UTC
DescriptionIn the Linux kernel, the following vulnerability has been resolved: mm: fix __vm_normal_page() to handle missing support for pmd_special()/pud_special() On x86 32-bit with THP enabled, zap_huge_pmd() is seen to generate a "WARNING: mm/memory.c:735 at __vm_normal_page+0x6a/0x7d", from the VM_WARN_ON_ONCE(is_zero_pfn(pfn) || is_huge_zero_pfn(pfn)); followed by "BUG: Bad rss-counter state"s, then later "BUG: Bad page state"s when reclaim gets to call shrink_huge_zero_folio_scan(). It's as if the _PAGE_SPECIAL bit never got set in the huge_zero pmd: and indeed, whereas pte_special() and pte_mkspecial() are subject to a dedicated CONFIG_ARCH_HAS_PTE_SPECIAL, pmd_special() and pmd_mkspecial() are subject to CONFIG_ARCH_SUPPORTS_PMD_PFNMAP, which is never enabled on any 32-bit architecture. While the problem was exposed through commit d80a9cb1a64a ("mm/huge_memory: add and use normal_or_softleaf_folio_pmd()"), it was an oversight in commit af38538801c6 ("mm/memory: factor out common code from vm_normal_page_*()") and would result in other problems: * huge zero folio accounted in smaps, pagemap (PAGE_IS_FILE) and numamaps as file-backed THP * folio_walk_start() returning the folio even without FW_ZEROPAGE set. Callers seem to tolerate that, though. ... and triggering the VM_WARN_ON_ONE(), although never reported so far. To fix it, teach vm_normal_page_pmd()/vm_normal_page_pud() to consider whether pmd_special/pud_special is actually implemented.

Vendor Declared Affected Products

SourceVendorProductVersionPlatforms
CNA Linux Linux affected af38538801c6a97565b44700ee6695d7d60ad779 62153767e8fc3889bc6508e9ffe927aaf64c4334 git Not specified
CNA Linux Linux affected af38538801c6a97565b44700ee6695d7d60ad779 9052ea2ee2233be5d4786b8909151ca2bfbedf99 git Not specified
CNA Linux Linux affected af38538801c6a97565b44700ee6695d7d60ad779 c0c6ccd9828c3a1950623b546fa57292a77b5c73 git Not specified
CNA Linux Linux affected 6.18 Not specified
CNA Linux Linux unaffected 6.18 semver Not specified
CNA Linux Linux unaffected 6.18.34 6.18.* semver Not specified
CNA Linux Linux unaffected 7.0.11 7.0.* semver Not specified
CNA Linux Linux unaffected 7.1 * original_commit_for_fix Not specified

References

ReferenceSourceLinkTags
git.kernel.org/stable/c/62153767e8fc3889bc6508e9ffe927aaf64c4334 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/9052ea2ee2233be5d4786b8909151ca2bfbedf99 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/c0c6ccd9828c3a1950623b546fa57292a77b5c73 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
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