FKIE_CVE-2026-53155

Vulnerability from fkie_nvd - Published: 2026-06-25 09:16 - Updated: 2026-06-30 14:44
Severity
Summary
In the Linux kernel, the following vulnerability has been resolved: mm/huge_memory: use correct flags for device private PMD entry Commit 65edfda6f3f2 ("mm/rmap: extend rmap and migration support device-private entries") updated set_pmd_migration_entry() to use pmdp_huge_get_and_clear() in the softleaf case, but made no further adjustments to the function itself. Therefore this function continues to incorrectly use pmd_write(), pmd_soft_dirty() and pmd_uffd_wp() to determine whether the installed migration entry should be marked writable, softdirty or uffd-wp respectively. Whilst all are incorrect, the most problematic of these is pmd_write(), as this can lead to corrupted rmap state. On x86-64 _PAGE_SWP_SOFT_DIRTY is aliased to _PAGE_RW. So calling pmd_write() on a softleaf will return the softdirty state encoded in the entry, assuming CONFIG_MEM_SOFT_DIRTY was enabled. This was observed when running the hmm.hmm_device_private.anon_write_child selftest: 1. The test faults in a range then migrates it such that a device-private THP range is established. 2. The parent then migrates it to a device-private writable PMD entry whose folio is entirely AnonExclusive with entire_mapcount=1, softdirty set (accidentally correct write state). 3. The parent forks and the PMD entries are set to device-private read only entries, entire_mapcount=2, softdirty still set. 4. [BUG] The child writes to the range then migrates to RAM - intending to install non-writable migration entries - but replacing parent and child PMD mappings with WRITABLE entries due to misinterpreting the softdirty bit. 5. In remove_migration_pmd(), if !softleaf_is_migration_read(entry) we set the RMAP_EXCLUSIVE flag when calling folio_add_anon_rmap_pmd() for both parent and child, which are therefore AnonExclusive. 6. [SPLAT] Child sets migrated folio entire_mapcount=1, parent sets entire_mapcount=2 and we end up with an AnonExclusive folio with entire_mapcount=2! Assert fires in __folio_add_anon_rmap(): VM_WARN_ON_FOLIO(folio_test_large(folio) && folio_entire_mapcount(folio) > 1 && PageAnonExclusive(cur_page), folio) This patch fixes the issue by correctly referencing the softleaf entry fields for writable, softdirty and uffd-wp in set_pmd_migration_entry(). It also only updates A/D flags if the entry is present as these are otherwise not meaningful for a softleaf entry. This patch also flips the if (!present) { ... } else { ... } logic in set_pmd_migration_entry() so it is easier to understand, and adds some comments to make things clearer. I was able to bisect this to commit 775465fd26a3 ("lib/test_hmm: add zone device private THP test infrastructure") which first exposes this bug as it was the commit that permitted test_hmm to generate the test. However commit 65edfda6f3f2 ("mm/rmap: extend rmap and migration support device-private entries") is the commit that actually enabled this behaviour.
References
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/43e7f189769c512c843184a8a5892ac779a6bd90
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/d7251c8d3f7cea76543abac6cf4ed15582c10846
Impacted products
Vendor Product Version
To clipboard 

{
  "affected": [
    {
      "affectedData": [
        {
          "defaultStatus": "unaffected",
          "product": "Linux",
          "programFiles": [
            "mm/huge_memory.c"
          ],
          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
          "vendor": "Linux",
          "versions": [
            {
              "lessThan": "d7251c8d3f7cea76543abac6cf4ed15582c10846",
              "status": "affected",
              "version": "65edfda6f3f2e58f757485a056e4f1775a1404a8",
              "versionType": "git"
            },
            {
              "lessThan": "43e7f189769c512c843184a8a5892ac779a6bd90",
              "status": "affected",
              "version": "65edfda6f3f2e58f757485a056e4f1775a1404a8",
              "versionType": "git"
            }
          ]
        },
        {
          "defaultStatus": "affected",
          "product": "Linux",
          "programFiles": [
            "mm/huge_memory.c"
          ],
          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
          "vendor": "Linux",
          "versions": [
            {
              "status": "affected",
              "version": "6.19"
            },
            {
              "lessThan": "6.19",
              "status": "unaffected",
              "version": "0",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "7.0.*",
              "status": "unaffected",
              "version": "7.0.13",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "*",
              "status": "unaffected",
              "version": "7.1",
              "versionType": "original_commit_for_fix"
            }
          ]
        }
      ],
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
    }
  ],
  "cveTags": [],
  "descriptions": [
    {
      "lang": "en",
      "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nmm/huge_memory: use correct flags for device private PMD entry\n\nCommit 65edfda6f3f2 (\"mm/rmap: extend rmap and migration support\ndevice-private entries\") updated set_pmd_migration_entry() to use\npmdp_huge_get_and_clear() in the softleaf case, but made no further\nadjustments to the function itself.\n\nTherefore this function continues to incorrectly use pmd_write(),\npmd_soft_dirty() and pmd_uffd_wp() to determine whether the installed\nmigration entry should be marked writable, softdirty or uffd-wp\nrespectively.\n\nWhilst all are incorrect, the most problematic of these is pmd_write(), as\nthis can lead to corrupted rmap state.\n\nOn x86-64 _PAGE_SWP_SOFT_DIRTY is aliased to _PAGE_RW.  So calling\npmd_write() on a softleaf will return the softdirty state encoded in the\nentry, assuming CONFIG_MEM_SOFT_DIRTY was enabled.\n\nThis was observed when running the hmm.hmm_device_private.anon_write_child\nselftest:\n\n1. The test faults in a range then migrates it such that a device-private\n   THP range is established.\n\n2. The parent then migrates it to a device-private writable PMD entry whose\n   folio is entirely AnonExclusive with entire_mapcount=1, softdirty set\n   (accidentally correct write state).\n\n3. The parent forks and the PMD entries are set to device-private read only\n   entries, entire_mapcount=2, softdirty still set.\n\n4. [BUG] The child writes to the range then migrates to RAM - intending to\n   install non-writable migration entries - but replacing parent and child\n   PMD mappings with WRITABLE entries due to misinterpreting the softdirty\n   bit.\n\n5. In remove_migration_pmd(), if !softleaf_is_migration_read(entry) we\n   set the RMAP_EXCLUSIVE flag when calling folio_add_anon_rmap_pmd() for\n   both parent and child, which are therefore AnonExclusive.\n\n6. [SPLAT] Child sets migrated folio entire_mapcount=1, parent sets\n   entire_mapcount=2 and we end up with an AnonExclusive folio with\n   entire_mapcount=2! Assert fires in __folio_add_anon_rmap():\n\n\t\tVM_WARN_ON_FOLIO(folio_test_large(folio) \u0026\u0026\n\t\t\t\t folio_entire_mapcount(folio) \u003e 1 \u0026\u0026\n\t\t\t\t PageAnonExclusive(cur_page), folio)\n\nThis patch fixes the issue by correctly referencing the softleaf entry\nfields for writable, softdirty and uffd-wp in set_pmd_migration_entry().\n\nIt also only updates A/D flags if the entry is present as these are\notherwise not meaningful for a softleaf entry.\n\nThis patch also flips the if (!present) { ...  } else { ...  } logic in\nset_pmd_migration_entry() so it is easier to understand, and adds some\ncomments to make things clearer.\n\nI was able to bisect this to commit 775465fd26a3 (\"lib/test_hmm: add zone\ndevice private THP test infrastructure\") which first exposes this bug as\nit was the commit that permitted test_hmm to generate the test.\n\nHowever commit 65edfda6f3f2 (\"mm/rmap: extend rmap and migration support\ndevice-private entries\") is the commit that actually enabled this\nbehaviour."
    }
  ],
  "id": "CVE-2026-53155",
  "lastModified": "2026-06-30T14:44:27.313",
  "metrics": {},
  "published": "2026-06-25T09:16:32.877",
  "references": [
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "url": "https://git.kernel.org/stable/c/43e7f189769c512c843184a8a5892ac779a6bd90"
    },
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "url": "https://git.kernel.org/stable/c/d7251c8d3f7cea76543abac6cf4ed15582c10846"
    }
  ],
  "sourceIdentifier": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
  "vulnStatus": "Awaiting Analysis"
}


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