CVE-2026-23100 (GCVE-0-2026-23100)
Vulnerability from cvelistv5
Published
2026-02-04 16:08
Modified
2026-03-25 10:20
Severity ?
Summary
In the Linux kernel, the following vulnerability has been resolved: mm/hugetlb: fix hugetlb_pmd_shared() Patch series "mm/hugetlb: fixes for PMD table sharing (incl. using mmu_gather)", v3. One functional fix, one performance regression fix, and two related comment fixes. I cleaned up my prototype I recently shared [1] for the performance fix, deferring most of the cleanups I had in the prototype to a later point. While doing that I identified the other things. The goal of this patch set is to be backported to stable trees "fairly" easily. At least patch #1 and #4. Patch #1 fixes hugetlb_pmd_shared() not detecting any sharing Patch #2 + #3 are simple comment fixes that patch #4 interacts with. Patch #4 is a fix for the reported performance regression due to excessive IPI broadcasts during fork()+exit(). The last patch is all about TLB flushes, IPIs and mmu_gather. Read: complicated There are plenty of cleanups in the future to be had + one reasonable optimization on x86. But that's all out of scope for this series. Runtime tested, with a focus on fixing the performance regression using the original reproducer [2] on x86. This patch (of 4): We switched from (wrongly) using the page count to an independent shared count. Now, shared page tables have a refcount of 1 (excluding speculative references) and instead use ptdesc->pt_share_count to identify sharing. We didn't convert hugetlb_pmd_shared(), so right now, we would never detect a shared PMD table as such, because sharing/unsharing no longer touches the refcount of a PMD table. Page migration, like mbind() or migrate_pages() would allow for migrating folios mapped into such shared PMD tables, even though the folios are not exclusive. In smaps we would account them as "private" although they are "shared", and we would be wrongly setting the PM_MMAP_EXCLUSIVE in the pagemap interface. Fix it by properly using ptdesc_pmd_is_shared() in hugetlb_pmd_shared().
References
Impacted products
Vendor Product Version
Linux Linux Version: 02333ac1c35370517a19a4a131332a9690c6a5c7
Version: 56b274473d6e7e7375f2d0a2b4aca11d67c6b52f
Version: 2e31443a0d18ae43b9d29e02bf0563f07772193d
Version: 59d9094df3d79443937add8700b2ef1a866b1081
Version: 59d9094df3d79443937add8700b2ef1a866b1081
Version: 94b4b41d0cdf5cfd4d4325bc0e6e9e0d0e996133
Version: 8410996eb6fea116fe1483ed977aacf580eee7b4
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      "descriptions": [
        {
          "lang": "en",
          "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nmm/hugetlb: fix hugetlb_pmd_shared()\n\nPatch series \"mm/hugetlb: fixes for PMD table sharing (incl.  using\nmmu_gather)\", v3.\n\nOne functional fix, one performance regression fix, and two related\ncomment fixes.\n\nI cleaned up my prototype I recently shared [1] for the performance fix,\ndeferring most of the cleanups I had in the prototype to a later point. \nWhile doing that I identified the other things.\n\nThe goal of this patch set is to be backported to stable trees \"fairly\"\neasily. At least patch #1 and #4.\n\nPatch #1 fixes hugetlb_pmd_shared() not detecting any sharing\nPatch #2 + #3 are simple comment fixes that patch #4 interacts with.\nPatch #4 is a fix for the reported performance regression due to excessive\nIPI broadcasts during fork()+exit().\n\nThe last patch is all about TLB flushes, IPIs and mmu_gather.\nRead: complicated\n\nThere are plenty of cleanups in the future to be had + one reasonable\noptimization on x86. But that\u0027s all out of scope for this series.\n\nRuntime tested, with a focus on fixing the performance regression using\nthe original reproducer [2] on x86.\n\n\nThis patch (of 4):\n\nWe switched from (wrongly) using the page count to an independent shared\ncount.  Now, shared page tables have a refcount of 1 (excluding\nspeculative references) and instead use ptdesc-\u003ept_share_count to identify\nsharing.\n\nWe didn\u0027t convert hugetlb_pmd_shared(), so right now, we would never\ndetect a shared PMD table as such, because sharing/unsharing no longer\ntouches the refcount of a PMD table.\n\nPage migration, like mbind() or migrate_pages() would allow for migrating\nfolios mapped into such shared PMD tables, even though the folios are not\nexclusive.  In smaps we would account them as \"private\" although they are\n\"shared\", and we would be wrongly setting the PM_MMAP_EXCLUSIVE in the\npagemap interface.\n\nFix it by properly using ptdesc_pmd_is_shared() in hugetlb_pmd_shared()."
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2026-03-25T10:20:18.340Z",
        "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "shortName": "Linux"
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          "url": "https://git.kernel.org/stable/c/5b2aec77f92265a9028c5f632bdd9af5b57ec3a3"
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          "url": "https://git.kernel.org/stable/c/51dcf459845fd28f5a0d83d408a379b274ec5cc5"
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        {
          "url": "https://git.kernel.org/stable/c/ca1a47cd3f5f4c46ca188b1c9a27af87d1ab2216"
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      "title": "mm/hugetlb: fix hugetlb_pmd_shared()",
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    "assignerShortName": "Linux",
    "cveId": "CVE-2026-23100",
    "datePublished": "2026-02-04T16:08:22.592Z",
    "dateReserved": "2026-01-13T15:37:45.965Z",
    "dateUpdated": "2026-03-25T10:20:18.340Z",
    "state": "PUBLISHED"
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