[CVE-2026-98176][LOW] drm/amdkfd: Avoid integer underflow with ffs in EOP ring size calc

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

CVE: CVE-2026-98176
Priority: LOW
AL-KERNEL base severity: LOW
KPANIC flag: NO
Patch: drm/amdkfd: Avoid integer underflow with ffs in EOP ring size calc
Commit: 82e1b8299c6da02ce02185c208d2fdf7572b5ea1
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=82e1b8299c6da02ce02185c208d2fdf7572b5ea1
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98176
Analysis date: Thu, 08 Oct 2026 07:17:12 -0400
ActionableScore: 0
ActionableScore lower bound: unknown
Actionable bucket: Ordinary Moderate
Manual review required: NO

Summary:
No one-sentence report phrase was found.

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

The original Linux kernel CVE announcement for CVE-2026-98176 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98176

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-2026-98176	LOW	https://www.kernelcve.org/list/?q=CVE-2026-98176 CHECK WITH IMPACT FROM ORIG NN LOW | AEGIS IMPACT MODERATE_KPANIC AEGIS_AS=0 LEGACY=LOW RESULT=DIFF (legacy and Aegis reconciliation differ; DECISION: legacy LOW vs Aegis MODERATE_KPANIC)	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:N/A:L';CWE-191;CWE-682;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:N';BEST CVSS score: '2.5';DESCR 'A theoretical integer underflow exists in the amdkfd EOP ring size calculation when ffs returns zero or one. The normal KFD EOP ring size is at least 4096 bytes, so the affected expression is not reachable through the standard queue creation path described by the patch. No memory corruption, invalid memory access, kernel crash, or privilege escalation primitive is demonstrated. The base assessment is therefore CVSS 0.0. For the paranoid score, the CVSS PR:L assumption applies only if a future or external violation of the EOP ring size invariant allows a local KFD user to program an invalid GPU queue configuration. The worst defensible impact is limited local availability degradation. NO MANUAL CHECK REQUIRED COULD BE AUTOCLOSED.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate (with actual score 0)	MAYBE	OOB SIMPLEFIX HARDWARE  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=0
PrimitiveClass=NONE
RealUAF=NO
HostAdminRequired=UNKNOWN
NamespaceScopedPrivilege=UNKNOWN
ImportantCandidate=NO
ManualReview=NO
AutoDowngradeAllowed=YES

1. ActionableScore

* Raw conservative score: 0
* Conservative score: 0
* Raw paranoid score: 0
* Paranoid score: 0
* Final recommended bucket: **Ordinary Moderate**::

No floor or cap was applied. The theoretical underflow alone is not an established corruption, crash, availability, authorization, or lifetime primitive.

2. Signal breakdown

* +0 Integer arithmetic hardening. The old expression can theoretically compute a negative result if ffs returns zero or one, but the commit explicitly states that the EOP ring buffer cannot be smaller than 4096 bytes in practice.
* +0 Memory corruption. No OOB access, UAF, stale pointer, invalid dereference, invalid DMA operation, or incorrect memory ownership is established.
* +0 Availability impact. The patch does not demonstrate a GPU hang, kernel crash, queue corruption, or host-wide DoS caused by the theoretical underflow.
* +0 Local unprivileged trigger. The supplied material does not establish that a non-administrative user can violate the EOP ring size invariant through the complete KFD queue setup path.
* +0 Strong exploitation leverage. No controlled GPU queue corruption, attacker-selected register programming consequence, arbitrary write, or privilege escalation mechanism is shown.
* +0 Remote reachability. This is a local AMD KFD queue-management calculation and no network path is established.
* No negative privilege or hardware penalty was applied. There is no need to manufacture a penalty because the score has no positive security signals.

Important non-awarded signals:

* Controlled reclaim is not applicable and not demonstrated.
* Arbitrary write is not demonstrated.
* Kernel crash or device reset is not demonstrated.
* Confidentiality and integrity impact are not demonstrated.
* The theoretical possibility that a future change could permit an invalid EOP ring size is not scored as a currently reachable primitive.

3. Reachability analysis

The affected calculation is used while programming AMD KFD MQD queue state. The normal EOP ring size is stated to be at least 4096 bytes, which prevents ffs from returning the values needed for the subtractive expression to underflow.

The supplied patch does not show the complete allocation and validation path for q->eop_ring_buffer_size. Therefore it is not established whether a local unprivileged user, delegated graphics service, or host administrator could ever provide an undersized value. HostAdminRequired is UNKNOWN rather than YES or NO.

No namespace-specific capability path is shown. NamespaceScopedPrivilege is UNKNOWN. There is no remote trigger, no firmware-mediated external input path, no special race, and no demonstrated hardware fault requirement beyond use of the AMD KFD driver.

4. Primitive and severity interpretation

The exact issue is a theoretical signed arithmetic underflow in the conversion from EOP ring buffer size to a logarithmic hardware field value.

This is not a UAF, double free, refcount defect, OOB access, active-state retirement failure, semantic reinterpretation, or authorization bypass. There is no active structured stale object and no lifetime operation.

The patch-supported practical evidence says that the required invalid input cannot occur because the ring buffer size has a lower bound of 4096 bytes. Consequently, the patch is best interpreted as defensive correctness hardening that removes a fragile expression rather than remediation of an actionable security primitive.

PrimitiveClass is NONE. ImportantCandidate is NO because no meaningful exploitation leverage remains unresolved. AutoDowngradeAllowed is YES because the available evidence supports neither a reachable corruption primitive nor a non-DoS security consequence.

5. One-sentence report phrase

The amdkfd patch removes a theoretical ffs based integer underflow in EOP ring size encoding, but the required undersized ring buffer is not reachable through the normal KFD allocation path and no security impact is demonstrated.

6. Manual review recommendation

NO MANUAL CHECK NEEDED

The commit explicitly states that the minimum EOP ring size prevents the underflow condition in practice, and no crash, corruption, or privilege-boundary consequence is established.

7. Call-site confidence

Call-site confidence: medium

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

Patch: drm/amdkfd: Avoid integer underflow with ffs in EOP ring size calc
Commit: 82e1b8299c6da02ce02185c208d2fdf7572b5ea1
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=82e1b8299c6da02ce02185c208d2fdf7572b5ea1

Commit description:

The low 6 bits of cp_hqd_eop_control store the base-2 logarithm
of the EOP ring size. This was calculated as

ffs(q->eop_ring_buffer_size / sizeof(unsigned int)) - 1 - 1

But ffs can in theory return 1 or 0, so this could underflow
(although in practice the ring buffer size cannot be less than 4096).

Change this to

ffs(q->eop_ring_buffer_size / sizeof(unsigned int) / 4)

using properties of logarithms.

Reviewed-by: Kent Russell <kent.russell@amd.com>
Signed-off-by: David Francis <David.Francis@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
(cherry picked from commit 4f18c56 )
Cc: stable@vger.kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  drivers/gpu/drm/amd/amdkfd/kfd_mqd_manager_v10.c
  drivers/gpu/drm/amd/amdkfd/kfd_mqd_manager_v11.c
  drivers/gpu/drm/amd/amdkfd/kfd_mqd_manager_v12.c
  drivers/gpu/drm/amd/amdkfd/kfd_mqd_manager_v12_1.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=82e1b8299c6da02ce02185c208d2fdf7572b5ea1

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

The original Linux kernel CVE announcement for CVE-2026-98176 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98176

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:N/A:N
  The Best / paranoid CVSS vector: AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:L
  The Best / paranoid CVSS score: 2.5

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: unknown
  Paranoid ActionableScore: 0

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).