[CVE-2026-80686][MODERATE REGULAR] mm: migrate_device: fix pte_pfn/pte_dirty called on non-present PTE [ Upstream

[AL-KERNEL <alkernel@kernelcve.org>]

CVE: CVE-2026-80686
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: mm: migrate_device: fix pte_pfn/pte_dirty called on non-present PTE [ Upstream
Commit: 26f9ca8ed42cba25d2c75daff13561cce6019395
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=26f9ca8ed42cba25d2c75daff13561cce6019395
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-80686
Analysis date: Fri, 28 Aug 2026 06:14:57 -0400
ActionableScore: 4
ActionableScore lower bound: 3
Actionable bucket: Borderline Actionable Moderate / Manual review recommended
Manual review required: YES

Summary:
migrate_vma_collect_pmd could call pte_pfn() or pte_dirty() on a non present PTE during device memory migration, allowing a local workload with access to the affected migration path to cause a kernel crash or limited dirty accounting integrity impact.

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ABOUT THIS REPORT
======================================================================

The original Linux kernel CVE announcement for CVE-2026-80686 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-80686

The original announcement does not normally provide a security severity
estimate, CVSS assessment, or enough information to determine whether the
reported kernel bug represents a practically relevant security issue.

This report was generated by AL-KERNEL, an AI-assisted Linux kernel
vulnerability analysis system developed by Alexander Larkin. It combines
an autonomous classifier with LLM-assisted technical analysis and a
separate ActionableScore mechanism.

The purpose of this report is to prioritize Linux kernel CVEs before
manual review, identify cases that require prompt investigation, and
support automatic closure of issues that are unlikely to have meaningful
security impact.

Published priority for this report: MODERATE REGULAR
Manual review required: YES

A detailed explanation of the methodology and priority rules is included
at the end of this message.

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AL-KERNEL CLASSIFICATION RESULT
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CVE-2026-80686	MODERATE	CHECK WITH IMPACT FROM ORIG NN MODERATE	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:L/A:H';CWE-754;CWE-703;CWE-682;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:L/A:H';BEST CVSS score: '5.8';DESCR 'migrate_vma_collect_pmd could call pte_pfn() and pte_dirty() on a non present PTE such as a device private entry. This is undefined for non present entries and may crash the kernel or produce incorrect dirty folio accounting during device memory migration. For the CVSS the PR:L is used because a local user or process must be able to exercise a driver or device path that invokes migrate_vma. The issue is not network reachable and depends on systems using device private memory or HMM style migration paths. Impact is at least local denial of service via kernel crash, with limited integrity risk from wrong dirty accounting and limited confidentiality risk only in the paranoid interpretation.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Borderline Actionable Moderate / Manual review recommended (with actual score 4)	YES	DANGER INIT SIMPLEFIX HARDWARE MEMORY  DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN5	YES	NO	checked

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ACTIONABLESCORE ANALYSIS
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ActionableScore=4
ActionableScoreLower=3

## 1. ActionableScore

* Conservative score: 3
* Paranoid score: 4
* Final recommended bucket: **Borderline Actionable Moderate / Manual review recommended**::

## 2. Signal breakdown

* Local unprivileged trigger: +1
  A local process may be able to exercise migrate_vma through a device driver using HMM or device private memory paths.

* Reliable kernel crash / strong DoS: +1
  The commit explicitly says pte_pfn() on a non present PTE may crash.

* Integrity impact plausible: +1
  Incorrect pte_dirty() handling may cause wrong dirty folio accounting during migration, which is a limited data integrity concern.

* Rare AND difficult-to-reach subsystem/configuration: -1
  The issue depends on migrate_device / HMM style paths and non present device private entries, not a generic syscall path.

* Hard or special triggering conditions: -1
  Triggering requires a specific migration path and PTE state. It is not a simple always reachable local bug.

* Paranoid extra mm impact concern: +1
  The affected code is in memory migration and handles PTE state. Undefined PTE interpretation in mm code deserves manual review even without a proven UAF or write primitive.

## 3. Reachability analysis

The bug is local, not network reachable. A realistic trigger requires a system using device private memory or HMM style migration, commonly via GPU or accelerator related drivers. It does not normally require full root if an unprivileged local workload can access the relevant device path, but it is configuration and hardware dependent. Namespaces do not obviously make this broadly reachable by themselves.

## 4. Severity interpretation

This behaves more like a borderline actionable Moderate than an Important vulnerability. The patch shows undefined handling of non present PTEs and a plausible crash, plus possible dirty accounting integrity impact. It does not show UAF, double free, OOB write, arbitrary write, attacker controlled reclaim, or a concrete privilege escalation primitive. Theoretical memory-management risk exists, but realistic evidence supports DoS and limited integrity concern rather than LPE.

## 5. One-sentence report phrase

migrate_vma_collect_pmd could call pte_pfn() or pte_dirty() on a non present PTE during device memory migration, allowing a local workload with access to the affected migration path to cause a kernel crash or limited dirty accounting integrity impact.

## 6. Manual review recommendation

MANUAL CHECK RECOMMENDED

Reason: this is mm/PTE handling code with undefined behavior and possible integrity effects, but the patch does not demonstrate a strong memory corruption or privilege escalation primitive.

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UPSTREAM PATCH SUMMARY
======================================================================

Patch: mm: migrate_device: fix pte_pfn/pte_dirty called on non-present PTE [ Upstream
Commit: 26f9ca8ed42cba25d2c75daff13561cce6019395
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=26f9ca8ed42cba25d2c75daff13561cce6019395

Changed files:
  mm/migrate_device.c

Diff excerpt:

Not included in this email. See the upstream URL for the full patch.

Full patch:
https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=26f9ca8ed42cba25d2c75daff13561cce6019395

======================================================================
DETAILED REPORT METHODOLOGY
======================================================================

The original Linux kernel CVE announcement for CVE-2026-80686 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-80686

The original CVE announcement normally does not include a security-level
estimate. In particular, it may not contain a CVSS assessment, an impact
level, or enough information to determine whether the reported bug is a
practically relevant security issue. One purpose of this parallel CVE list
is to provide that missing technical and prioritization information.

The original goal of the AL-KERNEL project was to prioritize Linux kernel
CVE analysis automatically before manual review. The system can also help
identify non-security issues that may be suitable for automatic closure.

This report was generated by AL-KERNEL, an AI-assisted Linux kernel
vulnerability analysis system developed by Alexander Larkin.

The first analysis stage combines an autonomous classifier with additional
LLM-based analysis. The autonomous classifier runs locally on a CPU and is
based on a backpropagation neural network. Together, these mechanisms
produce a technical vulnerability description, identify likely weakness
types, estimate CVSS severity, and provide input for ActionableScore.

Two CVSS estimates are retained because incomplete kernel vulnerability
information often permits more than one defensible interpretation:

  Conservative CVSS vector: AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:L/A:H
  The Best / paranoid CVSS vector: AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:L/A:H
  The Best / paranoid CVSS score: 5.8

The conservative vector represents a lower-impact interpretation.
The Best/paranoid vector intentionally represents a plausible upper-bound
interpretation and should not automatically be treated as demonstrated
real-world impact.

CVSS may also need to be adjusted for a particular Linux deployment,
because actual reachability, privileges, enabled kernel configuration,
hardware, namespaces, exposed device nodes, and other environmental
conditions can differ significantly between systems.

A separate ActionableScore mechanism evaluates practical remediation
urgency. Its analysis may include reachability, attack prerequisites,
subsystem exposure, memory-corruption characteristics, denial-of-service
reliability, and possible confidentiality, integrity, or
privilege-escalation impact.

  Conservative ActionableScore: 3
  Paranoid ActionableScore: 4

The final base severity is taken directly from the second tab-separated
field of the AL-KERNEL classification result. ActionableScore does not
replace or independently override that final AL-KERNEL decision, and
if ActionableScore adjusted impact level of ALKERNEL, then you would see
self-readable flags above like INCREASED_TO_HIGH_BASED_ON_ACTIONABLESCOREHIGHEREQTHAN7.

For an AL-KERNEL result of MODERATE, this report uses the following
additional presentation split:

  ActionableScore below 5   -> MODERATE REGULAR
  ActionableScore 5 or more -> MODERATE 7.0

The distinction between MODERATE REGULAR and MODERATE 7.0 makes it
possible to identify Moderate issues that should receive manual analysis
and fixes before lower-priority MODERATE REGULAR issues. In many cases,
MODERATE REGULAR fixes may wait for a later rebase or routine update.

There is one override in which MODERATE REGULAR becomes MODERATE 7.0
even when the ActionableScore is below 5. When the AL-KERNEL result
contains the KPANIC flag, a MODERATE result is always presented as
MODERATE 7.0. The KPANIC flag selected with few regexps without
usage of AI at all, so it helps to detect cases when Kernel Crash happens
and similar (to filter False-Negative results from the LLM usage).

KPANIC indicates that a reliable kernel crash, kernel panic, or similarly
serious kernel availability impact was identified by the classification
workflow.

AL-KERNEL base severity for this report: MODERATE
KPANIC detected for this report: NO
Published priority for this report (same as in Subject): MODERATE REGULAR

These results are intended to support engineering triage. They are
machine-generated estimates, and cases marked for manual review should
be validated by a human security engineer before final disposition.
For more info read docs linked from here: https://kernelcve.org/
(and you can submit you own patch there to generate such a report
for non-existant CVE-id yet).

Note that in many cases this AI tool selects higher severity, than
real is (means you can expect Importants instead of Moderate 7.0 or
Moderates 7.0 instead of regular Moderates). If you see such cases,
please use reply email interface to add additional manual analyses
info to this particular CVE.
And please, please, let me know when you see Lows instead of Importants
or Important instead of Low (because particular for such cases I
need to tune this AI tool to make it better for this one and next similar).
My contact email for such notifications is alexanjelausa@gmail.com (and both
send reply to CVE record itself too and see "reply" button below for howto reply).