CVE-2026-63875 (GCVE-0-2026-63875)
Vulnerability from cvelistv5
Published
2026-07-19 14:54
Modified
2026-10-19 20:17
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: arm64: tlb: Flush walk cache when unsharing PMD tables When huge_pmd_unshare() is called to unshare a PMD table, the tlb_unshare_pmd_ptdesc() function sets tlb->unshared_tables=true but the aarch64 tlb_flush() only checked tlb->freed_tables to determine whether to use TLBF_NONE (vae1is, invalidates walk cache) or TLBF_NOWALKCACHE (vale1is, leaf-only). This caused the stale PMD page table entry to remain in the walk cache after unshare, potentially leading to incorrect page table walks. Fix by including unshared_tables in the check, so that when unsharing tables, TLBF_NONE is used and the walk cache is properly invalidated. Here is the detailed distinction between vae1is and vale1is: | Instruction Combination | Actual Invalidation Scope | | ------------------------ | --------------------------------------------------| | `VAE1IS` + TTL=`0` | All entries at all levels (full invalidation) | | `VAE1IS` + TTL=`2` (L2) | Non-leaf at Level 0/1 + leaf at Level 2 | | `VALE1IS` + TTL=`0` | Leaf entries at all levels (non-leaf not cleared) | | `VALE1IS` + TTL=`2` (L2) | Leaf entry at Level 2 only |
References
Impacted products
Vendor Product Version
Linux Linux Version: 6495204f8219a57859669d618b25d06176d5a872
Version: ce4cf24761467756462c0e1dbe4a5e9c9eb520fc
Version: daa6707b71a2da23a82979fa21f788aeb706f1a2
Version: ff37dd18ce7739a26aab0cc2d31006a45e6bde63
Version: da06bb0ca45b1ca6f1ab55023e34e61a520337f3
Version: 9b671f6f432be07c0ddd66e437d6d0e0db684f83
Version: 8ce720d5bd91e9dc16db3604aa4b1bf76770a9a1
Version: 8ce720d5bd91e9dc16db3604aa4b1bf76770a9a1
Version: 5.10.253   ≤
Version: 5.15.203   ≤
Version: 6.1.167   ≤
Version: 6.6.127   ≤
Version: 6.12.74   ≤
Version: 6.18.13   ≤
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          "value": "In the Linux kernel, the following vulnerability has been resolved:\n\narm64: tlb: Flush walk cache when unsharing PMD tables\n\nWhen huge_pmd_unshare() is called to unshare a PMD table, the\ntlb_unshare_pmd_ptdesc() function sets tlb-\u003eunshared_tables=true\nbut the aarch64 tlb_flush() only checked tlb-\u003efreed_tables to\ndetermine whether to use TLBF_NONE (vae1is, invalidates walk\ncache) or TLBF_NOWALKCACHE (vale1is, leaf-only).\n\nThis caused the stale PMD page table entry to remain in the walk cache\nafter unshare, potentially leading to incorrect page table walks.\n\nFix by including unshared_tables in the check, so that when\nunsharing tables, TLBF_NONE is used and the walk cache is properly\ninvalidated.\n\nHere is the detailed distinction between vae1is and vale1is:\n\n| Instruction Combination  | Actual Invalidation Scope                         |\n| ------------------------ | --------------------------------------------------|\n| `VAE1IS`  + TTL=`0`      | All entries at all levels (full invalidation)     |\n| `VAE1IS`  + TTL=`2` (L2) | Non-leaf at Level 0/1 + leaf at Level 2           |\n| `VALE1IS` + TTL=`0`      | Leaf entries at all levels (non-leaf not cleared) |\n| `VALE1IS` + TTL=`2` (L2) | Leaf entry at Level 2 only                        |"
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              "value": "AV:L - The vulnerable `tlb_flush()` path is only reached through local memory-management syscalls (mmap/munmap/mprotect/mremap/fork) operating on hugetlb VMAs, not through any network-facing kernel service.\nAC:L - An attacker fully controls the trigger sequence\u2014creating shared hugetlbfs mappings (\u22651GB PUD-aligned), forking to establish shared PMD tables, and concurrently unmapping/mprotecting/mremapping to force `huge_pmd_unshare()`\u2014with no conditions outside their control.\nPR:L - Exploitation requires only an unprivileged local user capable of mapping shared hugetlb pages via hugetlbfs or SHM_HUGETLB, which is commonly available on arm64 database and container hosts with pre-reserved huge pages.\nUI:N - No victim interaction is required; the attacker sets up and triggers the stale walk-cache condition entirely within processes they control.\nS:U - Impact is confined to kernel memory-management within the same security authority (incorrect page-table walks and cross-mapping leakage within the kernel), not a VM escape or cross-authority boundary break.\nC:H - Stale non-leaf walk-cache entries after `pud_clear()` can cause incorrect page-table walks, enabling reads of memory that should be unmapped or mapped to different physical pages, constituting an arbitrary memory read primitive.\nI:H - Incorrect translations from stale PMD walk-cache entries can direct stores to unintended physical pages, and freed/reused page-table pages reached via stale cache entries provide a write/corruption primitive exploitable for control-flow hijacking.\nA:H - Stale walk-cache pointers to cleared or freed page-table structures can cause kernel faults, oops, or panics during page walks or concurrent GUP-fast access on the affected address space."
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        "dateUpdated": "2026-08-05T12:36:48.899Z",
        "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "shortName": "Linux"
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          "url": "https://git.kernel.org/stable/c/47490bbb05c8c0e09cc3cfd237d8934ffc340583"
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        {
          "url": "https://git.kernel.org/stable/c/0199c9d57861f17b556b6cba1f765c7cce79745b"
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          "url": "https://git.kernel.org/stable/c/d766a49d9b55705c4737cd8bb5d3faa2d31330fd"
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          "url": "https://git.kernel.org/stable/c/8ca7284da0e67b3e71d90ec17f08286774245ad9"
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          "url": "https://git.kernel.org/stable/c/48125cd9c55cbe297b59fd1f9bda48b0960bd181"
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        {
          "url": "https://git.kernel.org/stable/c/c2ff4764e03e7a8d758352f4aceb8fe1be6ac971"
        }
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      "title": "arm64: tlb: Flush walk cache when unsharing PMD tables",
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    "assignerShortName": "Linux",
    "cveId": "CVE-2026-63875",
    "datePublished": "2026-07-19T14:54:48.842Z",
    "dateReserved": "2026-07-19T07:54:57.017Z",
    "dateUpdated": "2026-10-19T20:17:53.723Z",
    "state": "PUBLISHED"
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  "dataType": "CVE_RECORD",
  "dataVersion": "5.2"
}


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