CVE-2025-68179 (GCVE-0-2025-68179)
Vulnerability from cvelistv5
Published
2025-12-16 13:42
Modified
2026-08-05 12:10
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: s390: Disable ARCH_WANT_OPTIMIZE_HUGETLB_VMEMMAP As reported by Luiz Capitulino enabling HVO on s390 leads to reproducible crashes. The problem is that kernel page tables are modified without flushing corresponding TLB entries. Even if it looks like the empty flush_tlb_all() implementation on s390 is the problem, it is actually a different problem: on s390 it is not allowed to replace an active/valid page table entry with another valid page table entry without the detour over an invalid entry. A direct replacement may lead to random crashes and/or data corruption. In order to invalidate an entry special instructions have to be used (e.g. ipte or idte). Alternatively there are also special instructions available which allow to replace a valid entry with a different valid entry (e.g. crdte or cspg). Given that the HVO code currently does not provide the hooks to allow for an implementation which is compliant with the s390 architecture requirements, disable ARCH_WANT_OPTIMIZE_HUGETLB_VMEMMAP again, which is basically a revert of the original patch which enabled it.
References
Impacted products
Vendor Product Version
Linux Linux Version: 00a34d5a99c0631bd780b14cbe3813d0b39c3886
Version: 00a34d5a99c0631bd780b14cbe3813d0b39c3886
Version: 00a34d5a99c0631bd780b14cbe3813d0b39c3886
Version: 00a34d5a99c0631bd780b14cbe3813d0b39c3886
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{
  "containers": {
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          "defaultStatus": "unaffected",
          "product": "Linux",
          "programFiles": [
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              "versionType": "original_commit_for_fix"
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              "negate": false,
              "operator": "OR"
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      ],
      "descriptions": [
        {
          "lang": "en",
          "value": "In the Linux kernel, the following vulnerability has been resolved:\n\ns390: Disable ARCH_WANT_OPTIMIZE_HUGETLB_VMEMMAP\n\nAs reported by Luiz Capitulino enabling HVO on s390 leads to reproducible\ncrashes. The problem is that kernel page tables are modified without\nflushing corresponding TLB entries.\n\nEven if it looks like the empty flush_tlb_all() implementation on s390 is\nthe problem, it is actually a different problem: on s390 it is not allowed\nto replace an active/valid page table entry with another valid page table\nentry without the detour over an invalid entry. A direct replacement may\nlead to random crashes and/or data corruption.\n\nIn order to invalidate an entry special instructions have to be used\n(e.g. ipte or idte). Alternatively there are also special instructions\navailable which allow to replace a valid entry with a different valid\nentry (e.g. crdte or cspg).\n\nGiven that the HVO code currently does not provide the hooks to allow for\nan implementation which is compliant with the s390 architecture\nrequirements, disable ARCH_WANT_OPTIMIZE_HUGETLB_VMEMMAP again, which is\nbasically a revert of the original patch which enabled it."
        }
      ],
      "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 vulnerable HVO remap code is reached through local hugetlb pool operations \u2014 `mmap(MAP_HUGETLB)`/`munmap` driving surplus folio allocation and free, or sysfs/sysctl pool resizing \u2014 all requiring local system access. There is no network-facing path to `hugetlb_vmemmap_optimize_folio()`.\nAC:L - Every HVO optimize/restore cycle unconditionally performs the architecturally illegal valid-to-valid page table entry replacement and, in the batched path, frees vmemmap pages with zero TLB invalidation because s390\u0027s `flush_tlb_all()` is empty; the reporter confirmed reproducible crashes and an attacker can repeat the allocate/free loop indefinitely to compound the stale-TLB window.\nPR:L - On a system with HVO enabled and `nr_overcommit_hugepages` configured \u2014 the exact deployment the s390 enabling commit documents \u2014 an ordinary unprivileged user triggers `alloc_surplus_hugetlb_folio()` \u2192 `hugetlb_vmemmap_optimize_folio()` via `mmap(MAP_HUGETLB|MAP_ANONYMOUS)`, which has no capability check in `mm/mmap.c:586`. Access to a world-writable hugetlbfs mount gives the same unprivileged reach.\nUI:N - The attacker triggers the hugetlb allocation and free cycle entirely on their own; no victim action, file open, or filesystem mount by another user is needed.\nS:U - The corruption is confined to the kernel\u0027s own page tables and physical memory within a single security authority; there is no crossing of a hypervisor, IOMMU, or sandbox boundary.\nC:H - Stale writable TLB entries continue to map vmemmap virtual addresses to physical pages already returned to the buddy allocator and reallocated for arbitrary kernel or user data, giving read access to that memory; additionally, a mixed old/new translation can resolve to an arbitrary physical address, and corrupted `struct page` metadata can expose page contents across process boundaries.\nI:H - The commit explicitly states the direct entry replacement \"may lead to random crashes and/or data corruption\"; kernel writes to `struct page` through stale RW mappings land in reallocated physical pages, and the corrupted refcount/flags/mapping fields are readily leveraged into arbitrary write and control-flow hijacking primitives.\nA:H - The reporter observed reproducible kernel crashes with HVO enabled on s390, and the attacker can re-trigger the condition at will to reliably panic the system."
            }
          ]
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2026-08-05T12:10:03.176Z",
        "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "shortName": "Linux"
      },
      "references": [
        {
          "url": "https://git.kernel.org/stable/c/7088465f10816d9425b95740b37c95f082041d76"
        },
        {
          "url": "https://git.kernel.org/stable/c/5e23918e4352288323d13fb511116cdea0234b71"
        },
        {
          "url": "https://git.kernel.org/stable/c/d4a8238e5729505b7394ccb007e5dc3e557aa66b"
        },
        {
          "url": "https://git.kernel.org/stable/c/64e2f60f355e556337fcffe80b9bcff1b22c9c42"
        }
      ],
      "title": "s390: Disable ARCH_WANT_OPTIMIZE_HUGETLB_VMEMMAP",
      "x_generator": {
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  "cveMetadata": {
    "assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
    "assignerShortName": "Linux",
    "cveId": "CVE-2025-68179",
    "datePublished": "2025-12-16T13:42:57.817Z",
    "dateReserved": "2025-12-16T13:41:40.251Z",
    "dateUpdated": "2026-08-05T12:10:03.176Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.2"
}


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