# CVE-2026-89758

## Summary

- **CVE ID:** CVE-2026-89758
- **Severity:** HIGH
- **CVSS Score:** 7.8 (CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H)
- **CWE:** N/A
- **Published:** Sep 11, 2026
- **Last Modified:** Sep 13, 2026

## Description

In the Linux kernel, the following vulnerability has been resolved:

mm/mempolicy: skip non-present PMDs when queueing folios

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.

## Affected Products

- Linux — Linux (368076f52ebeecd33e10a9f80905d7508b6b6149)
- Linux — Linux (6.19)
- Linux — Linux (0)
- Linux — Linux (7.2.4)
- Linux — Linux (7.3-rc1)

## References

- [CNA](https://git.kernel.org/stable/c/3d927093b2add7ced588a926c3dc5d7a83f18596)
- [CNA](https://git.kernel.org/stable/c/2858b4027f491e6fdb8ee2d8923798b619bf2791)

## Exploitation Prediction (EPSS)

- **EPSS Score:** 0.14%
- **EPSS Percentile:** 4.0

---
_Exported from OnDuty AI Vulnerability Intelligence on 2026-09-17._