{"id":"DEBIAN-CVE-2026-53155","details":"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():  \t\tVM_WARN_ON_FOLIO(folio_test_large(folio) && \t\t\t\t folio_entire_mapcount(folio) \u003e 1 && \t\t\t\t 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.","modified":"2026-08-27T23:06:25.596531518Z","published":"2026-06-25T09:16:32.877Z","upstream":["CVE-2026-53155"],"references":[{"type":"ADVISORY","url":"https://security-tracker.debian.org/tracker/CVE-2026-53155"}],"affected":[{"package":{"name":"linux","ecosystem":"Debian:14","purl":"pkg:deb/debian/linux?arch=source&distro=forky"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"7.0.13-1"}]}],"versions":["6.12.100-1","6.12.101-1","6.12.105-1","6.12.38-1","6.12.41-1","6.12.43-1","6.12.43-1~bpo12+1","6.12.48-1","6.12.57-1","6.12.57-1~bpo12+1","6.12.63-1","6.12.63-1~bpo12+1","6.12.69-1","6.12.69-1~bpo12+1","6.12.73-1","6.12.73-1~bpo12+1","6.12.74-1","6.12.74-2","6.12.74-2~bpo12+1","6.12.85-1","6.12.85-1~bpo12+1","6.12.86-1","6.12.86-1~bpo12+1","6.12.88-1","6.12.88-1~bpo12+1","6.12.90-1","6.12.90-1~bpo12+1","6.12.90-2","6.12.90-2~bpo12+1","6.12.94-1","6.12.94-1~bpo12+1","6.12.95-1","6.12.95-1~bpo12+1","6.12.96-1","6.13.10-1~exp1","6.13.11-1~exp1","6.13.2-1~exp1","6.13.3-1~exp1","6.13.4-1~exp1","6.13.5-1~exp1","6.13.6-1~exp1","6.13.7-1~exp1","6.13.8-1~exp1","6.13.9-1~exp1","6.13~rc6-1~exp1","6.13~rc7-1~exp1","6.14.3-1~exp1","6.14.5-1~exp1","6.14.6-1~exp1","6.15-1~exp1","6.15.1-1~exp1","6.15.2-1~exp1","6.15.3-1~exp1","6.15.4-1~exp1","6.15.5-1~exp1","6.15.6-1~exp1","6.15~rc7-1~exp1","6.16-1~exp1","6.16.1-1~exp1","6.16.10-1","6.16.11-1","6.16.12-1","6.16.12-1~bpo13+1","6.16.12-2","6.16.3-1","6.16.3-1~bpo13+1","6.16.5-1","6.16.6-1","6.16.7-1","6.16.8-1","6.16.9-1","6.16~rc7-1~exp1","6.17.10-1","6.17.11-1","6.17.12-1","6.17.13-1","6.17.13-1~bpo13+1","6.17.2-1~exp1","6.17.5-1~exp1","6.17.6-1","6.17.7-1","6.17.7-2","6.17.8-1","6.17.8-1~bpo13+1","6.17.9-1","6.18.1-1~exp1","6.18.10-1","6.18.12-1","6.18.12-1~bpo13+1","6.18.13-1","6.18.14-1","6.18.15-1","6.18.15-1~bpo13+1","6.18.2-1~exp1","6.18.3-1","6.18.5-1","6.18.5-1~bpo13+1","6.18.8-1","6.18.9-1","6.18.9-1~bpo13+1","6.18~rc4-1~exp1","6.18~rc4-1~exp2","6.18~rc5-1~exp1","6.18~rc6-1~exp1","6.18~rc7-1~exp1","6.19-1~exp1","6.19.10-1","6.19.10-1~bpo13+1","6.19.11-1","6.19.11-1~bpo13+1","6.19.12-1","6.19.13-1","6.19.13-1~bpo13+1","6.19.14-1","6.19.14-1~bpo13+1","6.19.2-1~exp1","6.19.3-1~exp1","6.19.4-1~exp1","6.19.5-1~exp1","6.19.6-1","6.19.6-2","6.19.6-2~bpo13+1","6.19.8-1","6.19.8-1~bpo13+1","6.19~rc4-1~exp1","6.19~rc5-1~exp1","6.19~rc6-1~exp1","6.19~rc7-1~exp1","6.19~rc8-1~exp1","7.0-1~exp1","7.0.1-1~exp1","7.0.10-1","7.0.10-1~bpo13+1","7.0.12-1","7.0.12-2","7.0.12-2~bpo13+1","7.0.13-1~bpo13+1","7.0.3-1","7.0.4-1","7.0.4-1~bpo13+1","7.0.7-1","7.0.7-1~bpo13+1","7.0.9-1","7.0.9-1~bpo13+1"],"ecosystem_specific":{"urgency":"not yet assigned"},"database_specific":{"source":"https://storage.googleapis.com/osv-test-debian-osv/debian-cve-osv/DEBIAN-CVE-2026-53155.json"}}],"schema_version":"1.9.0","severity":[{"type":"CVSS_V3","score":"CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H"}]}