CVE-2026-64181 (GCVE-0-2026-64181)
Vulnerability from cvelistv5
Published
2026-07-19 15:41
Modified
2026-08-05 12:39
Severity ?
7.8 (High) - CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
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.
References
Impacted products
Vendor Product Version
Linux Linux Version: af38538801c6a97565b44700ee6695d7d60ad779
Version: af38538801c6a97565b44700ee6695d7d60ad779
Version: af38538801c6a97565b44700ee6695d7d60ad779
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{
  "containers": {
    "cna": {
      "affected": [
        {
          "defaultStatus": "unaffected",
          "product": "Linux",
          "programFiles": [
            "mm/memory.c"
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          "vendor": "Linux",
          "versions": [
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              "version": "6.18"
            },
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              "status": "unaffected",
              "version": "0",
              "versionType": "semver"
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              "versionType": "semver"
            },
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              "lessThanOrEqual": "7.0.*",
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              "version": "7.0.11",
              "versionType": "semver"
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              "lessThanOrEqual": "*",
              "status": "unaffected",
              "version": "7.1",
              "versionType": "original_commit_for_fix"
            }
          ]
        }
      ],
      "cpeApplicability": [
        {
          "nodes": [
            {
              "cpeMatch": [
                {
                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                  "versionEndExcluding": "6.18.34",
                  "versionStartIncluding": "6.18",
                  "vulnerable": true
                },
                {
                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
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                  "vulnerable": true
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              ],
              "negate": false,
              "operator": "OR"
            }
          ]
        }
      ],
      "descriptions": [
        {
          "lang": "en",
          "value": "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\u0027s 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."
        }
      ],
      "metrics": [
        {
          "cvssV3_1": {
            "baseScore": 7.8,
            "baseSeverity": "HIGH",
            "vectorString": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H",
            "version": "3.1"
          },
          "scenarios": [
            {
              "lang": "en",
              "value": "AV:L - The bug is reached only through local memory-management syscalls (mmap, madvise, munmap, process teardown) that walk page tables and call zap_huge_pmd() \u2192 vm_normal_page_pmd() \u2192 __vm_normal_page(); there is no network, adjacent, or physical attack path.\nAC:L - On affected 32-bit THP configurations an unprivileged attacker can deterministically create a huge zero PMD (mmap + MADV_HUGEPAGE + read fault) and trigger the bug (munmap or MADV_DONTNEED) without races or conditions outside their control.\nPR:L - Exploitation requires only an unprivileged local user manipulating their own address space via standard syscalls; no root, capabilities, or authentication is needed.\nUI:N - No victim interaction is required; the attacker fully controls the memory mappings and the syscalls that trigger page-table zapping.\nS:U - Impact is confined to kernel memory-management corruption and accounting within the kernel security boundary; this is not a VM escape, IOMMU bypass, or cross-authority sandbox escape.\nC:H - Misclassifying the shared huge zero folio as a normal page corrupts global rmap/mapcount state on a system-wide singleton folio, triggers VM_WARN/BUG checks, and misreports mappings in /proc/pagemap and smaps\u2014memory corruption with plausible information-disclosure leverage.\nI:H - Incorrect rmap removal and RSS accounting on the global huge_zero_folio corrupts kernel memory metadata system-wide; callers such as KSM (vm_normal_page_pmd) may treat the zero folio as a normal anonymous folio, enabling cross-mapping integrity corruption beyond the attacker\u0027s VMA.\nA:H - The bug triggers VM_WARN_ON_ONCE, \"BUG: Bad rss-counter state\" on mm teardown, and \"BUG: Bad page state\" during shrink_huge_zero_folio_scan() reclaim, any of which can crash or destabilize the kernel on affected systems."
            }
          ]
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2026-08-05T12:39:56.626Z",
        "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "shortName": "Linux"
      },
      "references": [
        {
          "url": "https://git.kernel.org/stable/c/62153767e8fc3889bc6508e9ffe927aaf64c4334"
        },
        {
          "url": "https://git.kernel.org/stable/c/9052ea2ee2233be5d4786b8909151ca2bfbedf99"
        },
        {
          "url": "https://git.kernel.org/stable/c/c0c6ccd9828c3a1950623b546fa57292a77b5c73"
        }
      ],
      "title": "mm: fix __vm_normal_page() to handle missing support for pmd_special()/pud_special()",
      "x_generator": {
        "engine": "bippy-1.2.0"
      }
    }
  },
  "cveMetadata": {
    "assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
    "assignerShortName": "Linux",
    "cveId": "CVE-2026-64181",
    "datePublished": "2026-07-19T15:41:04.455Z",
    "dateReserved": "2026-07-19T07:54:57.039Z",
    "dateUpdated": "2026-08-05T12:39:56.626Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.2"
}


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