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CVE-2026-89758
mm/mempolicy: skip non-present PMDs when queueing folios
Published 2026-09-11 (37 days ago) by the Linux kernel CNA. Subsystem mm. Debian urgency: unimportant.
What to do, per Debian release
Debian's own status for CVE-2026-89758 in every release this site tracks, and what each one means in practice. Every status below is the one the Debian Security Team publishes for this CVE. source
| Release | Status | Version | What this means |
|---|---|---|---|
| Debian 12bookworm | not affected | 6.1.190-1 | Nothing to do. bookworm never shipped the vulnerable code. |
| Debian 13trixie | not affected | 6.12.113-1 | Nothing to do. trixie never shipped the vulnerable code. |
| Debian 14forky | fixed | 7.2.6-1 | Update the kernel and reboot. Fixed in 7.2.6-1. A running kernel keeps the old code until the machine restarts. |
| Debian unstablesid | fixed | 7.2.6-1 | Update the kernel and reboot. Fixed in 7.2.6-1. A running kernel keeps the old code until the machine restarts. |
The vulnerability
What the bug is
Patch series "mm: handle device-private PMDs in walk callbacks", v3. Since commit 368076f52ebe ("mm/huge_memory: add device-private THP support to PMD operations") a PMD may hold a device-private swap entry whenever an HMM-based GPU driver migrates an anonymous THP folio to device memory via migrate_vma_pages(). pmd_trans_huge_lock() succeeds for such PMDs (pmd_is_huge() returns true for any non-present, non-none huge PMD), so several MM walk callbacks that used to assume present THP or migration entry are now reachable with a device-private PMD. The results range from a VM_BUG_ON() firing on debug kernels, to an oops on a bogus vmemmap dereference, to silently isolating an unrelated live folio from LRU in the aliasing case. This patch (of 3): queue_folios_pmd() is called under pmd_trans_huge_lock(), whose pmd_is_huge() check returns true for any non-present, non-none PMD softleaf. Passing such a PMD to pmd_folio() treats the softleaf encoding as a hardware PFN and can return a bogus folio pointer. Mirror queue_folios_pte_range(): handle non-present entries before looking up a folio. Keep migration entries counted as failures, but skip other non-present PMDs such as device-private entries. Potential trigger: an HMM-based GPU driver migrates an anonymous THP folio to device memory via migrate_vma_pages(), leaving a device-private PMD. Userspace then calls mbind(), migrate_pages() or set_mempolicy_home_node() on that range.
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/mempolicy.c
- What this is
- MEMORY MANAGEMENT - MEMORY POLICY AND MIGRATIONMAINTAINERS section matched on mm/mempolicy.c · linux-mm@kvack.org · Maintained
Check it on the machine
grep -w CONFIG_NUMA /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 armhf/armmp, armhf/armmp-lpae, armhf/rt/armmp, i386/686, i386/686-pae, i386/rt/686-pae
- trixieYnot built on armel/rpi, armhf/armmp, armhf/armmp-lpae, armhf/rt/armmp, s390x/s390x
- forky, sidYnot built on armhf/armmp, armhf/armmp-lpae, s390x/s390x
- Y
- built in where it is built at all; some flavours do not build it
- Build switch
- CONFIG_NUMA
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
- 2026-09-11 (37 days ago)source
- CVSS
- 7.8 high
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:Hsource recompute it - Attack vector
- local (AV:L)source
- EPSS
- 0.17%, higher than 5.4% 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 | 7.2.4 | 3d927093b2ad |
| 6.19 | 7.3 | 2858b4027f49 |
Why the CNA scored it this way
Quoted from the kernel CNA's own scoring file, word for word. A highlighted metric carries the most severe value CVSS v3.1 defines for it, which is what pushes the score up. source
- AV:LAttack vector, local
- queue_folios_pmd() is reached only from local mbind() and migrate_pages() via do_mbind()/do_migrate_pages() -> queue_pages_range() -> walk_page_range(); it is not a network, Bluetooth, or USB packet path.
- AC:LAttack complexity, low
- An attacker with GPU/HMM access can deterministically migrate an anonymous THP to device memory (leaving a device-private PMD) and then call mbind()/migrate_pages() on that range; no victim state or attacker-uncontrollable race is required.
- PR:LPrivileges required, low
- mbind() and self migrate_pages() are unprivileged; MPOL_MF_MOVE needs no capability. Device-private THP is created through ordinary DRM render-node/HMM usage (AMD KFD, Intel Xe, nouveau), not init-namespace root.
- UI:NUser interaction, none
- The attacker creates the device-private THP mapping and issues mbind() or migrate_pages() entirely in their own process; no other user must mount, open, or otherwise act.
- S:UScope, unchanged
- Impact is host-kernel MM corruption (bogus folio lookup and LRU isolation) within the same security authority; it is not a VM guest-to-host escape, IOMMU bypass, or sandbox breakout.
- C:HConfidentiality impact, high
- pmd_folio() treats a device-private PMD as a present THP and returns a bogus folio; aliasing isolates and migrates an unrelated live folio, a memory-corruption primitive usable for arbitrary kernel/user memory disclosure.
- I:HIntegrity impact, high
- The same bogus folio can be isolated from the LRU and handed to migrate_pages(), silently moving an unrelated live folio and enabling use-after-free, page-table corruption, and control-flow hijack.
- A:HAvailability impact, high
- A bogus vmemmap dereference oopses the kernel, debug builds hit VM_BUG_ON, and isolating or migrating the wrong folio can panic or hang the system.