[CVE-2026-45894][MODERATE 7.0] iommu/vt-d: Clear Present bit before tearing down PASID entry [ Upstream

[CVE-2026-45894][MODERATE 7.0] iommu/vt-d: Clear Present bit before tearing down PASID entry [ Upstream

[AL-KERNEL]

CVE: CVE-2026-45894
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: iommu/vt-d: Clear Present bit before tearing down PASID entry [ Upstream
Commit: a84d30e8d2bacd21782a6481158b7c9c552f4868
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=a84d30e8d2bacd21782a6481158b7c9c552f4868
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-45894
Analysis date: Wed, 27 May 2026 22:46:22 -0400
ActionableScore: 7
ActionableScore lower bound: 4
Actionable bucket: Strong Important candidate / Actionable Moderate at minimum
Manual review required: YES

Summary:
An Intel VT-d PASID teardown race can expose a torn PASID entry to IOMMU hardware, causing IOMMU faults and potentially affecting DMA translation isolation.

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

The original Linux kernel CVE announcement for CVE-2026-45894 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-45894

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 7.0
Manual review required: YES

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

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

CVE-2026-45894	MODERATE	CHECK	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H';CWE-362;CWE-667;CWE-693;Other CVSS 'AV:L/AC:H/PR:H/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '7';DESCR 'An Intel VT-d PASID teardown race can zero a 64 byte PASID entry while the Present bit is still visible to IOMMU hardware. Hardware may fetch the entry in multiple transactions and observe a torn state, which can cause IOMMU faults or potentially inconsistent DMA translation state. For the CVSS the PR:L is used in the paranoid score because delegated access to PASID capable devices, SVA, accelerators, or device assignment workflows can expose PASID lifecycle events below full host root, while typical host management remains privileged. The issue is not network reachable. Impact is at least denial of service through IOMMU faults. Because PASID entries define device DMA translation and isolation, worst case confidentiality and integrity impact cannot be ruled out without manual review.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Strong Important candidate / Actionable Moderate at minimum (with actual score 6) 	MAYBE	INIT HARDWARE KPANIC MEMORY 	-	-	checked

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

ActionableScore=7
ActionableScoreLower=4

## 1. ActionableScore

* Conservative score: 4
* Paranoid score: 7
* Final recommended bucket: **Strong Important candidate / Actionable Moderate at minimum**::

## 2. Signal breakdown

* Privileged device-management / DMA-adjacent corruption path: +1
  The bug affects Intel VT-d PASID translation entries, which are hardware-consumed DMA translation metadata.

* Cross-boundary isolation concern: +1
  PASID entries are part of DMA isolation and address-translation boundaries for devices, SVA, and assigned-device style workflows.

* Availability impact realistic: +1
  A torn PASID entry can cause IOMMU faults, device faults, or broken device operation.

* Confidentiality and integrity impact plausible in paranoid scoring: +2
  Because PASID entries define DMA translation state, inconsistent hardware-visible state could theoretically affect DMA isolation. The patch does not prove an exploit, but the isolation boundary makes this nontrivial.

* Security-boundary bypass concern in paranoid scoring: +2
  The affected state belongs to the IOMMU security boundary. If stale or torn translation state is observable by hardware, manual review is needed to exclude isolation bypass.

* Local/delegated device access in paranoid scoring: +1
  Some environments expose PASID-capable devices, SVA, accelerators, or device assignment workflows to less-than-full-host-root users.

* Requires privileged management in typical deployments: -2 conservative
  PASID teardown is normally controlled by kernel/device-management paths, not ordinary unprivileged syscalls.

* Hard hardware race / timing condition: -1
  The issue depends on concurrent CPU update and IOMMU hardware fetch of a multi-transaction PASID entry.

* No proven arbitrary write or direct LPE primitive: +0
  The patch shows hardware-visible translation-state race, not a demonstrated controlled overwrite or exploit chain.

## 3. Reachability analysis

Typical triggering requires PASID lifecycle activity on Intel VT-d scalable mode systems, usually through privileged device management, SVA, VFIO-like assignment, accelerator use, or driver teardown paths. In some deployments, PASID-capable devices may be delegated to containers, VMs, service accounts, or user-space accelerator frameworks, which lowers practical privilege assumptions.

This is not network reachable. The concerning boundary is DMA/IOMMU isolation, not packet parsing.

## 4. Severity interpretation

This is not ordinary kernel heap memory corruption, but it is more serious than a normal DoS bug because it affects hardware-visible DMA translation state. The demonstrated impact is likely IOMMU/device faults. The theoretical worst case includes DMA isolation inconsistency, so it should be treated as an Important candidate until manual review rules out confidentiality or integrity impact.

## 5. One-sentence report phrase

An Intel VT-d PASID teardown race can expose a torn PASID entry to IOMMU hardware, causing IOMMU faults and potentially affecting DMA translation isolation.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED

This touches PASID/IOMMU translation state, which is a DMA isolation boundary. Even without a demonstrated exploit, torn hardware-visible translation metadata should not be auto-closed.

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

Patch: iommu/vt-d: Clear Present bit before tearing down PASID entry [ Upstream
Commit: a84d30e8d2bacd21782a6481158b7c9c552f4868
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=a84d30e8d2bacd21782a6481158b7c9c552f4868

Changed files:
  drivers/iommu/intel/pasid.c
  drivers/iommu/intel/pasid.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=a84d30e8d2bacd21782a6481158b7c9c552f4868

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

The original Linux kernel CVE announcement for CVE-2026-45894 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-45894

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:H
  The Best / paranoid CVSS vector: AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H
  The Best / paranoid CVSS score: 7

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: 4
  Paranoid ActionableScore: 7

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: YES
Published priority for this report (same as in Subject): MODERATE 7.0

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).