CVE-2026-53155

What the bug is

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.

Where it lives

The fix touches these files. If the subsystem is one you do not use, the practical exposure is lower, though the package is still the vulnerable one.

mm/huge_memory.c

What this is

MEMORY MANAGEMENT - THP (TRANSPARENT HUGE PAGE)MAINTAINERS section matched on mm/huge_memory.c · linux-mm@kvack.org · Maintained

Check it on the machine

grep -w CONFIG_TRANSPARENT_HUGEPAGE /boot/config-$(uname -r)

Reads the booted kernel's own configuration, on the machine and nowhere else. =y is built in, =m is a module, and an is not set line means the code is not there.

Show whether Debian builds this, per release

Debian builds this, but not on every flavour. At least one release below builds the code on some of its kernel flavours and not on others, so the answer depends on the architecture and flavour installed.

• bookwormYnot built on amd64/rt/amd64, arm64/rt/arm64, armhf/armmp, armhf/rt/armmp, i386/rt/686-pae
• trixieYnot built on amd64/rt/amd64, arm64/rt/arm64, armel/rpi, armhf/armmp, armhf/rt/armmp
• forky, sidYnot built on amd64/rt-amd64, arm64/rt-arm64, armhf/armmp

Y

built in where it is built at all; some flavours do not build it

Build switch

CONFIG_TRANSPARENT_HUGEPAGE

From the configuration Debian publishes for every kernel flavour it builds. It covers only the architectures Debian ships a linux-config package for, and nothing about a kernel you built yourself. Debian's own status above stays authoritative about the source package.MAINTAINERS kbuild Makefiles Debian linux-config packages

Signals

Published

2026-06-25 (4 months ago)source

CVSS

no vector published, unrated

Attack vector

not published

EPSS

0.11%, higher than 1.1% of all CVEssource

CISA KEV

not listedthe KEV catalogue

Debian urgency

unimportantsource

Subsystem

mm

Upstream fixes

The versions the CNA records as introducing and fixing this, and the commit for each. source

Introduced	Fixed in	Commit
6.19	7.0.13	d7251c8d3f7c
6.19	7.1	43e7f189769c