{"cve":"CVE-2026-53155","nvd":{"published":"2026-06-25T09:16:32.877","modified":"2026-07-07T20:10:10.803","status":"Analyzed","description":"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) &&\n\t\t\t\t folio_entire_mapcount(folio) > 1 &&\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.","cvss_v4":null,"cvss_v3":{"version":"3.1","vector":"CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H","score":5.5},"cwes":[],"references":["https://git.kernel.org/stable/c/43e7f189769c512c843184a8a5892ac779a6bd90","https://git.kernel.org/stable/c/d7251c8d3f7cea76543abac6cf4ed15582c10846"],"products":["linux:linux_kernel"],"source":"nvd","synced_at":"2026-10-19T22:41:17.107060303+00:00"},"epss":{"cve":"CVE-2026-53155","score":0.00143,"percentile":0.03619,"date":"2026-10-31"},"kev":null,"osv":[],"attribution":["This product uses the NVD API but is not endorsed or certified by the NVD.","EPSS scores: FIRST Exploit Prediction Scoring System, https://www.first.org/epss","Known exploited vulnerabilities: CISA Known Exploited Vulnerabilities Catalog, https://www.cisa.gov/known-exploited-vulnerabilities-catalog","Package advisories: OSV (https://osv.dev), from the GitHub Advisory Database, PyPA, Go, RustSec and other ecosystem databases, under CC-BY 4.0 or CC0","CVE records: the CVE Program's CVE List (https://www.cve.org), under its terms of use (https://www.cve.org/Legal/TermsOfUse). CVE is a registered trademark of The MITRE Corporation; this product is not affiliated with the CVE Program."]}