[CVE-2026-98004][MODERATE REGULAR] iommu/riscv: Serialize command queue publishing [ Upstream

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

CVE: CVE-2026-98004
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: iommu/riscv: Serialize command queue publishing [ Upstream
Commit: 6d4c12ab9ab8db87411c863a54e0e97f9197afde
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=6d4c12ab9ab8db87411c863a54e0e97f9197afde
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98004
Analysis date: Fri, 25 Sep 2026 20:28:01 -0400
ActionableScore: 3
ActionableScore lower bound: 2
Actionable bucket: Borderline / manual review recommended
Manual review required: YES

Summary:
No one-sentence report phrase was found.

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

The original Linux kernel CVE announcement for CVE-2026-98004 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98004

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.

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

CVE-2026-98004	MODERATE	https://www.kernelcve.org/list/?q=CVE-2026-98004 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:L/I:L/A:H';CWE-362;CWE-667;CWE-662;Other CVSS 'AV:L/AC:H/PR:H/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '5.8';DESCR 'A race in the RISC-V IOMMU command queue can allow software producer state to advance before a command is fully written and published to hardware. Concurrent producers can observe inconsistent prod, tail, and head values, while a stale hardware head value can incorrectly advance the shadow head across a ring wrap. This may cause commands to be lost, processed out of order, or leave the queue stalled, resulting in device failures or a host denial of service. For the CVSS the PR:L value is used for the paranoid score because a local user with delegated VFIO, passthrough, or virtualization access may generate intensive IOMMU activity without full host administrative privileges. AC:H applies because successful triggering depends on concurrent queue publication and a suitable timing window. The issue is not directly network reachable. Impact is reliably availability related, while limited confidentiality or integrity impact is possible if lost or misordered invalidation commands weaken DMA translation consistency.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Borderline / manual review recommended (with actual score 3)  SKIP CVE-2026-98004 UNKNOWN SKIP The Fixes patch not applied yet, so unlikely that actual: url YES  NO NO unknown 	MAYBE	LOCK ERRORPATH DMAorINTERRUPT HARDWARE MEMORY  DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN4	-	-	checked

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

ActionableScore=3
ActionableScoreLower=2
PrimitiveClass=CLASS_C
RealUAF=NO
HostAdminRequired=UNKNOWN
NamespaceScopedPrivilege=UNKNOWN
ImportantCandidate=NO
ManualReview=RECOMMENDED
AutoDowngradeAllowed=YES

1. ActionableScore

* Raw conservative score: 2
* Conservative score: 2
* Raw paranoid score: 3
* Paranoid score: 3
* No floor or cap was applied.
* Final recommended bucket: **Borderline / manual review recommended**::

2. Signal breakdown

Conservative signals:

* +1 Memory and ring-state invariant restoration. The old implementation advanced `prod` before command storage and hardware publication were complete, while concurrent CPUs could observe inconsistent `prod`, `tail`, and `head` state.
* +1 Availability impact. Premature shadow-head advancement, command loss, command reordering, or a stalled command queue can disrupt IOMMU and attached-device operation.
* Total: 2.

Paranoid additional signal:

* +1 High-value device-management state. The inconsistent entries are active IOMMU command descriptors rather than passive diagnostics. Lost or misordered invalidation or synchronization commands could affect DMA translation consistency, although the supplied code does not establish an unauthorized DMA access primitive.
* Total: 3.

Not awarded:

* No UAF, OOB access, arbitrary write, controlled reclaim, refcount corruption, or callback influence is established.
* No confidentiality or integrity point is awarded because neither unauthorized DMA access nor modification of protected memory is demonstrated.
* No reliable kernel-crash point is awarded. The patch supports queue failure and device disruption, but not a confirmed host panic.
* No remote or local-unprivileged reachability point is awarded.
* No race penalty is applied because the patch does not establish that the interleaving is narrow, one-shot, or difficult to reproduce under concurrent command submission.
* No hardware or niche-subsystem penalty is applied merely because this is RISC-V IOMMU code.
* No active-translation synchronization point is awarded because the patch does not show a specific live mapping replacement, omitted TLB invalidation, or stale translation remaining operational.
* There is no repeated release or refcount operation, so the dedicated signal and UAF floors do not apply.

3. Reachability analysis

The vulnerable operation is an internal RISC-V IOMMU command-queue submission path. Triggering requires an active RISC-V IOMMU and concurrent command publication, potentially including a full queue or wraparound condition.

The supplied context does not identify callers or prove that an ordinary user, a VFIO process, a guest, or a namespace-scoped capability holder can drive the complete sequence. Delegated VFIO or passthrough access may generate IOMMU activity, but that alone does not prove control over the required concurrent submissions. Therefore `HostAdminRequired` and `NamespaceScopedPrivilege` remain `UNKNOWN`.

Prior platform support and an enabled RISC-V IOMMU are prerequisites. The attacker cannot instantiate the physical IOMMU through a namespace. The race appears workload-dependent, but there is insufficient evidence to classify it as a materially hard or one-shot timing race.

4. Primitive and severity interpretation

The exact primitive is inconsistent publication and consumption bookkeeping in a shared hardware command ring. Software producer state can become visible before the associated command is fully written and published. A stale hardware-head observation can also move the shadow head beyond commands that hardware has not consumed.

This is active queue-state corruption with demonstrated availability implications, but it is not a heap lifetime violation or CPU-memory corruption primitive. There is no stale object, post-lifetime access, repeated release, or refcount mutation. The evidence therefore supports `CLASS_C`, not Class A or Class B.

The demonstrated consequence is command loss, reordering, queue stalling, or device failure. A weakened DMA isolation boundary is a technically relevant review question because IOMMU commands include translation-management operations, but the supplied patch does not establish a specific stale translation, attacker-directed DMA target, or unauthorized memory access.

`ImportantCandidate=NO` because no independently useful corruption or boundary-bypass primitive is established. `AutoDowngradeAllowed=YES` because the demonstrated behavior remains an invalid-state and availability issue. Manual review is still recommended to confirm whether affected call sites can lose security-critical invalidation commands.

5. One-sentence report phrase

A race in RISC-V IOMMU command-queue publication can expose inconsistent producer and consumer state, causing commands to be lost or processed incorrectly and potentially stalling IOMMU or device operation, while no concrete memory-corruption or DMA-isolation bypass primitive is established.

6. Manual review recommendation

MANUAL CHECK RECOMMENDED

Review command types and callers to determine whether lost or reordered entries can suppress security-critical DMA invalidations rather than only causing queue or device failure.

7. Call-site confidence

Call-site confidence: medium

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

Patch: iommu/riscv: Serialize command queue publishing [ Upstream
Commit: 6d4c12ab9ab8db87411c863a54e0e97f9197afde
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=6d4c12ab9ab8db87411c863a54e0e97f9197afde

Changed files:
  drivers/iommu/riscv/iommu.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=6d4c12ab9ab8db87411c863a54e0e97f9197afde

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

The original Linux kernel CVE announcement for CVE-2026-98004 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98004

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: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: 2
  Paranoid ActionableScore: 3

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).