[CVE-2026-64151][LOW] iommupt: Check for missing PAGE_SIZE in the pgsize_bitmap [ Upstream

[CVE-2026-64151][LOW] iommupt: Check for missing PAGE_SIZE in the pgsize_bitmap [ Upstream

[AL-KERNEL]

CVE: CVE-2026-64151
Priority: LOW
AL-KERNEL base severity: LOW
KPANIC flag: NO
Patch: iommupt: Check for missing PAGE_SIZE in the pgsize_bitmap [ Upstream
Commit: 00850f41da24423587abd6124a790dd4f12bcef3
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=00850f41da24423587abd6124a790dd4f12bcef3
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64151
Analysis date: Sun, 19 Jul 2026 15:02:43 -0400
ActionableScore: 2
ActionableScore lower bound: 0
Actionable bucket: Ordinary Moderate / Low-like
Manual review required: NO

Summary:
The generic IOMMU page-table mapper could incorrectly use the PAGE_SIZE fast path even when PAGE_SIZE was not advertised in pgsize_bitmap, but the issue appears limited to unusual privileged IOMMU configurations with no demonstrated memory corruption or privilege-escalation primitive.

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

The original Linux kernel CVE announcement for CVE-2026-64151 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64151

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: LOW
Manual review required: NO

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

======================================================================
AL-KERNEL CLASSIFICATION RESULT
======================================================================

CVE-2026-64151	LOW	CHECK WITH IMPACT FROM ORIG NN LOW	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:L/A:L';CWE-754;CWE-682;CWE-693;Other CVSS 'AV:L/AC:H/PR:H/UI:N/S:U/C:N/I:N/A:L';BEST CVSS score: '3.6';DESCR 'generic_pt map_range could take the PAGE_SIZE fast path even when pgsize_bitmap did not advertise PAGE_SIZE support. This is a configuration and validation logic issue in an unusual IOMMU domain setup, and current upstream context says such a domain is not used with the DMA API today. For the CVSS the PR:L is used in the paranoid score because an untrusted local process with delegated VFIO or iommufd access could potentially exercise IOMMU map operations in some deployments, while the normal trigger requires administrative or driver level control. The issue is not network reachable. Impact is expected to be low and mainly limited to incorrect IOMMU mapping behavior or availability problems in unsupported configurations, with no evidence of UAF, OOB access, or arbitrary write.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate / Low-like (with actual score 1)  SKIP CVE-2026-64151 UNKNOWN SKIP No affected files built, so skip this CVE NO  - - unknown 	MAYBE	SIMPLEFIX DMAorINTERRUPT MEMORY  DECREASED_TO_MODERATE_REGULAR_FROM_MODERATE7_BASED_ON_GUESSCVSS DECREASED_TO_LOW_FROM_MODERATE_BASED_ON_ACTIONABLESCORELESSTHAN3	-	-	checked

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ACTIONABLESCORE ANALYSIS
======================================================================

ActionableScore=2
ActionableScoreLower=0

## 1. ActionableScore

* Conservative score: 0
* Paranoid score: 2
* Final recommended bucket: **Ordinary Moderate / Low-like**

## 2. Signal breakdown

Conservative signals:

* Requires admin/root/CAP_* in typical deployments: -2. Creating or configuring unusual IOMMU domains and driver page-size capabilities is normally privileged kernel/device-management activity.
* Rare AND difficult-to-reach subsystem/configuration: -1. The commit explicitly says dropping PAGE_SIZE from pgsize_bitmap is technically allowed but not done in practice, and such an iommu_domain is not used with the DMA API today.
* WARN_ON continuation / validation concern: +1. The old path could hit PT_WARN_ON and continue into the PAGE_SIZE fast path, but the patch does not show a concrete crash, UAF, OOB access, arbitrary write, or data disclosure.
* Score is floored at 0.

Paranoid signals:

* Local delegated trigger possibility: +1. In a conservative product model this is privileged, but in a more paranoid model delegated VFIO or iommufd access might allow a less privileged local actor to exercise IOMMU map operations.
* Integrity or availability concern from incorrect IOMMU mapping behavior: +1. If an unsupported page-size bitmap is actually exposed, taking the PAGE_SIZE fast path against the advertised capabilities could produce incorrect mapping behavior or device-visible inconsistency.
* No memory-corruption primitive counted. The patch does not show UAF, OOB write, double free, refcount misuse, stale callback, arbitrary write, or attacker-controlled overwrite.
* No reliable kernel crash counted. The evidence is a WARN_ON/design violation, not a demonstrated Oops, panic, or persistent DoS.

Call-site confidence: medium. The changed helper is in the IOMMU generic page-table mapping path, but the provided patch does not include concrete callers or a demonstrated failing runtime configuration.

## 3. Reachability analysis

The realistic trigger requires an IOMMU driver/domain configuration where PAGE_SIZE is missing from pgsize_bitmap while the generic page-table code still has system page-size support and receives a PAGE_SIZE mapping request. The commit says this is against design, but also says nothing currently does this and such a domain would not be used with the DMA API today. This makes ordinary unprivileged reachability unlikely.

Namespaces and containers do not normally make this reachable unless the product delegates VFIO/iommufd or similar device-management capabilities to an untrusted local user. There is no network path. There is no firmware-mediated external trigger shown by the patch.

## 4. Severity interpretation

This behaves like a low-risk validation/design-correctness issue rather than an Important-class kernel vulnerability. The theoretical concern is incorrect IOMMU mapping behavior in an unusual configuration, but the patch does not support memory corruption, privilege escalation, information disclosure, or a reliable crash primitive.

The paranoid score keeps a small nonzero value because IOMMU mapping bugs can affect trusted device/MMU state, and delegated device-management setups may reduce the effective privilege requirement. Even so, this remains below actionable Moderate because the affected configuration is uncommon and the patch context lacks a concrete downstream exploit primitive.

## 5. One-sentence report phrase

The generic IOMMU page-table mapper could incorrectly use the PAGE_SIZE fast path even when PAGE_SIZE was not advertised in pgsize_bitmap, but the issue appears limited to unusual privileged IOMMU configurations with no demonstrated memory corruption or privilege-escalation primitive.

## 6. Manual review recommendation

NO MANUAL CHECK NEEDED

This can be auto-closed or deferred for normal patch intake unless the evaluated product intentionally exposes delegated VFIO/iommufd or custom IOMMU domain creation to untrusted local users.

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

Patch: iommupt: Check for missing PAGE_SIZE in the pgsize_bitmap [ Upstream
Commit: 00850f41da24423587abd6124a790dd4f12bcef3
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=00850f41da24423587abd6124a790dd4f12bcef3

Changed files:
  drivers/iommu/generic_pt/iommu_pt.h

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=00850f41da24423587abd6124a790dd4f12bcef3

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

The original Linux kernel CVE announcement for CVE-2026-64151 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64151

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:H/UI:N/S:U/C:N/I:N/A:L
  The Best / paranoid CVSS vector: AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:L/A:L
  The Best / paranoid CVSS score: 3.6

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: 0
  Paranoid ActionableScore: 2

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: LOW
KPANIC detected for this report: NO
Published priority for this report (same as in Subject): LOW

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).