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CVE-2026-64181 (GCVE-0-2026-64181)

Vulnerability from cvelistv5 – Published: 2026-07-19 15:41 – Updated: 2026-08-05 12:39
VLAI
Title
mm: fix __vm_normal_page() to handle missing support for pmd_special()/pud_special()
Summary
In 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.
Severity
7.8 (High)
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
Assigner
References
Impacted products
Vendor Product Version CPE status
Linux Linux Affected: af38538801c6a97565b44700ee6695d7d60ad779 , < 62153767e8fc3889bc6508e9ffe927aaf64c4334 (git)
Affected: af38538801c6a97565b44700ee6695d7d60ad779 , < 9052ea2ee2233be5d4786b8909151ca2bfbedf99 (git)
Affected: af38538801c6a97565b44700ee6695d7d60ad779 , < c0c6ccd9828c3a1950623b546fa57292a77b5c73 (git)
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Linux Linux Affected: 6.18
Unaffected: 0 , < 6.18 (semver)
Unaffected: 6.18.34 , ≤ 6.18.* (semver)
Unaffected: 7.0.11 , ≤ 7.0.* (semver)
Unaffected: 7.1 , ≤ * (original_commit_for_fix)
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    "redhat_vex": {
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      "current_release_date": "2026-07-20T16:47:17+00:00",
      "cve": "CVE-2026-64181",
      "id": "CVE-2026-64181",
      "initial_release_date": "2026-07-19T00:00:00+00:00",
      "product_status:known_affected": "14",
      "product_status:known_not_affected": "260",
      "source": "Red Hat CSAF VEX",
      "status": "final",
      "title": "kernel: mm: fix __vm_normal_page() to handle missing support for pmd_special()/pud_special()",
      "url": "https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-64181.json",
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}



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Forecast uses a logistic model when the trend is rising, or an exponential decay model when the trend is falling. Fitted via linearized least squares.

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  • Seen: The vulnerability was mentioned, discussed, or observed by the user.
  • Confirmed: The vulnerability has been validated from an analyst's perspective.
  • Published Proof of Concept: A public proof of concept is available for this vulnerability.
  • Exploited: The vulnerability was observed as exploited by the user who reported the sighting.
  • Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
  • Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
  • Not confirmed: The user expressed doubt about the validity of the vulnerability.
  • Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.


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