[CVE-2026-89450][IMPORTANT] iommu/tegra241-cmdqv: Reject a vSID wider than the SID_MATCH field

[CVE-2026-89450][IMPORTANT] iommu/tegra241-cmdqv: Reject a vSID wider than the SID_MATCH field

[AL-KERNEL]

CVE: CVE-2026-89450
Priority: IMPORTANT
AL-KERNEL base severity: IMPORTANT
KPANIC flag: YES
Patch: iommu/tegra241-cmdqv: Reject a vSID wider than the SID_MATCH field
Commit: d903d99ffd22b0180bd745a43f221c21bcdd8d7c
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=d903d99ffd22b0180bd745a43f221c21bcdd8d7c
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89450
Analysis date: Sat, 12 Sep 2026 00:24:55 -0400
ActionableScore: 7
ActionableScore lower bound: 6
Actionable bucket: Strong Important candidate
Manual review required: YES

Summary:
No one-sentence report phrase was found.

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

The original Linux kernel CVE announcement for CVE-2026-89450 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89450

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: IMPORTANT
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-2026-89450	IMPORTANT	https://www.kernelcve.org/list/?q=CVE-2026-89450 CHECK WITH IMPACT FROM ORIG NN LOW	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:H';*CWE-20;CWE-197;CWE-284;Other CVSS 'AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H';BEST CVSS score: '8.8';DESCR 'A bounds check bug in the Tegra241 CMDQV IOMMU path allows a guest controlled vSID to be wider than the hardware SID_MATCH VIRT_SID field. Bits above the 20 bit field can be dropped when programming the register, so an oversized vSID may alias vSID 0 or another lower value and match the wrong Stream ID. For the CVSS the PR:L is used because reliable triggering requires a local VMM or userspace device assignment context with access to the IOMMUFD related interface, but not necessarily full host root privileges. The issue is not directly network reachable. Impact may include a DMA isolation or Stream ID translation bypass with high confidentiality, integrity, and availability impact in the worst defensible case. This should be reviewed manually because the affected code programs IOMMU matching state rather than only causing a crash or warning.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Strong Important candidate (with actual score 7)	YES	SIMPLEFIX IMPROVEONLY LINUS  KPANIC INCREASED_TO_HIGH_BASED_ON_GUESSCVSS8.5PLUS	YES	NO	checked

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

ActionableScore=7
ActionableScoreLower=6
PrimitiveClass=CLASS_A
RealUAF=NO
HostAdminRequired=UNKNOWN
NamespaceScopedPrivilege=NO
ImportantCandidate=YES
ManualReview=REQUIRED
AutoDowngradeAllowed=NO

1. ActionableScore

* Raw conservative score: 6
* Conservative score: 6. No floor or cap applied.
* Raw paranoid score: 7
* Paranoid score: 7. No floor or cap applied.
* Final recommended bucket: **Strong Important candidate**::

2. Signal breakdown

Conservative positive signals:

* +2 Strong attacker-influenced semantic reinterpretation. A guest or VMM supplied vSID is accepted under a wider integer range, then truncated when programmed into the 20 bit SID_MATCH hardware field, causing a different Stream ID to be matched.
* +2 Security-boundary / DMA isolation bypass. The affected register controls IOMMU Stream ID matching, so aliasing to vSID 0 or another lower value can select the wrong translation or isolation domain.
* +1 Confidentiality plausible. If the wrong Stream ID maps to a different DMA translation context, unauthorized DMA reads from a protected domain are a defensible consequence.
* +1 Integrity plausible. The same wrong Stream ID match may permit DMA writes or translation effects against a domain that should not be selected.

Conservative negative signals:

* No host-admin penalty applied. The input establishes VMM or userspace device-assignment reachability, but does not fully resolve whether host-admin-equivalent privilege is always required for the complete setup.
* No hardware rarity penalty applied. The bug is Tegra241-specific, but the patch concerns an intended IOMMU userspace/device-assignment feature rather than a purely physical-only debug path.

Paranoid additional signal:

* +1 Availability plausible. A wrong IOMMU Stream ID match can plausibly cause device faults, broken DMA isolation, or disruption of assigned-device operation beyond a harmless validation failure.

Important non-awarded signals:

* RealUAF not awarded because this is not a lifetime or stale-object bug.
* Controlled reclaim not demonstrated.
* Arbitrary kernel read/write not directly demonstrated.
* Remote reachability not established.
* Local ordinary unprivileged trigger not established.
* NamespaceScopedPrivilege not established.
* Repeated release/refcount signal not applicable.
* Stronger score above 7 not used because the patch establishes a strong isolation primitive, but not a demonstrated full exploit chain, root compromise, or arbitrary host memory access.

3. Reachability analysis

The direct triggering actor is described as a VMM because vdev->virt_id is guest-controlled and reaches tegra241_vintf_init_vsid through the iommufd vdevice path. This is a local virtualization or device-assignment control path, not a packet-processing or remote network path.

The complete privilege boundary is not fully resolved from the supplied patch. A VMM or userspace device-assignment process may be below full host root in some deployments, but initial device assignment or access to the relevant IOMMUFD resources may involve prior host policy or management setup. Therefore HostAdminRequired is UNKNOWN rather than YES or NO.

Namespace-scoped privilege is not established. The supplied evidence does not show that all required IOMMUFD and device-assignment operations can be performed inside attacker-created namespaces.

Prior privileged setup may exist in real deployments because assigned devices and IOMMUFD access are usually mediated by host policy. This does not erase the security relevance of the primitive once the VMM/device-assignment context is available.

No race is involved. The trigger is deterministic invalid value acceptance and hardware field truncation.

4. Primitive and severity interpretation

The exact primitive is an insufficient bounds check followed by truncation when programming an active IOMMU hardware match register. The old code allowed virt_sid values wider than the SID_MATCH VIRT_SID field and then wrote virt_sid shifted into the register, dropping upper bits. This can cause a guest-controlled or VMM-controlled vSID to alias a different Stream ID.

This is not fixed stale storage and not cleanup-only behavior. It is an active hardware translation or matching state bug in a security-sensitive IOMMU path.

PrimitiveClass is CLASS_A because the patch establishes a strong semantic reinterpretation and security-boundary primitive: an attacker-influenced identifier is interpreted as a different active Stream ID in IOMMU matching hardware.

The demonstrated consequence is wrong Stream ID matching. The practical security concern is DMA isolation or translation-domain bypass. The speculative consequence is full cross-domain memory compromise, but the patch alone does not demonstrate arbitrary host read/write or a complete privilege-escalation chain.

ImportantCandidate is YES because IOMMU Stream ID aliasing is a meaningful security-boundary primitive with plausible confidentiality and integrity consequences.

AutoDowngradeAllowed is NO because automatically closing this as ordinary validation cleanup would lose a concrete DMA/IOMMU isolation issue.

Likely operational severity is Important-class for affected Tegra241 CMDQV deployments using userspace device assignment or VMM-controlled vdevices.

5. One-sentence report phrase

A guest or VMM controlled vSID wider than the Tegra241 SID_MATCH field can be truncated when programmed into the IOMMU match register, causing aliasing to the wrong Stream ID and creating a potential DMA isolation bypass.

6. Manual review recommendation

MANUAL CHECK REQUIRED

The issue directly affects IOMMU Stream ID matching and can alias one virtual Stream ID to another, so the boundary impact depends on deployment-specific device assignment and translation-domain layout.

7. Call-site confidence

Call-site confidence: medium

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

Patch: iommu/tegra241-cmdqv: Reject a vSID wider than the SID_MATCH field
Commit: d903d99ffd22b0180bd745a43f221c21bcdd8d7c
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=d903d99ffd22b0180bd745a43f221c21bcdd8d7c

Commit description:

tegra241_vintf_init_vsid() programs the guest-provided vSID into SID_MATCH,
whose VIRT_SID field spans bits [20:1] with bit 0 as the match-enable flag.
The HW therefore matches only a 20-bit Stream ID.

The bound check rejects only virt_sid > UINT_MAX, which admits a value far
wider than the field. The write "virt_sid << 1 | 0x1" then drops every bit
above 20: a virt_sid of 0x80000000 lands as SID_MATCH = 0x1, a valid match
on vSID 0, so the entry aliases the wrong Stream ID. Because vdev->virt_id
is guest-controlled, a VMM can trigger it.

Validate virt_sid against the field width with FIELD_MAX(), and program the
register with FIELD_PREP() so the value and the field stay consistent.

Fixes: 4dc0d12 ("iommu/tegra241-cmdqv: Add user-space use support")
Cc: stable@vger.kernel.org
Assisted-by: Claude:claude-opus-4-8
Signed-off-by: Nicolin Chen <nicolinc@nvidia.com>
Signed-off-by: Will Deacon <will@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  drivers/iommu/arm/arm-smmu-v3/tegra241-cmdqv.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=d903d99ffd22b0180bd745a43f221c21bcdd8d7c

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

The original Linux kernel CVE announcement for CVE-2026-89450 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89450

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:L/PR:L/UI:N/S:U/C:H/I:H/A:H
  The Best / paranoid CVSS vector: AV:L/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:H
  The Best / paranoid CVSS score: 8.8

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: 6
  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: IMPORTANT
KPANIC detected for this report: YES
Published priority for this report (same as in Subject): IMPORTANT

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).