* [CVE-2026-98177][MODERATE REGULAR] drm/amdkfd: Avoid integer underflow in EOP ring size calculation.
@ 2026-10-08 17:19 21% AL-KERNEL
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From: AL-KERNEL @ 2026-10-08 17:19 UTC (permalink / raw)
To: kernel-cve
CVE: CVE-2026-98177
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: drm/amdkfd: Avoid integer underflow in EOP ring size calculation.
Commit: 287a34c4d712e0bdb67751e21316d9c8d75a528a
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=287a34c4d712e0bdb67751e21316d9c8d75a528a
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98177
Analysis date: Thu, 08 Oct 2026 13:19:32 -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-2026-98177 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98177
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: NO
A detailed explanation of the methodology and priority rules is included
at the end of this message.
======================================================================
AL-KERNEL CLASSIFICATION RESULT
======================================================================
CVE-2026-98177 MODERATE https://www.kernelcve.org/list/?q=CVE-2026-98177 CHECK WITH IMPACT FROM ORIG NN LOW | AEGIS IMPACT MODERATE AEGIS_AS=0 LEGACY=MODERATE RESULT=SAME (legacy and Aegis reconciliation agree; DECISION: both MODERATE) 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-191;CWE-682;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:L';BEST CVSS score: '5.8';DESCR 'An integer underflow was theoretically possible when the AMD KFD driver encoded the EOP ring size because order_base_2 could return zero before one was subtracted. The wrapped result could cause cp_hqd_eop_control to describe a ring larger than the allocated buffer, while the hardware does not correctly clamp this field. In normal operation the EOP ring cannot be smaller than 4096 bytes, so the vulnerable arithmetic boundary is not expected to be reachable through supported queue creation paths. For the CVSS the PR:L value is used because a local process with access to AMD KFD is required, although reliable triggering would also require bypassing the minimum ring size invariant. The issue is not network reachable. The demonstrated risk is at most local availability impact, while the paranoid assessment considers limited confidentiality or integrity impact only if the size invariant can be violated and the GPU then accesses memory beyond the actual ring.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate (with actual score 0) MAYBE OOB HARDWARE DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN4 - - guess
======================================================================
ACTIONABLESCORE ANALYSIS
======================================================================
ActionableScore=0
PrimitiveClass=NONE
RealUAF=NO
HostAdminRequired=UNKNOWN
NamespaceScopedPrivilege=UNKNOWN
ImportantCandidate=NO
ManualReview=RECOMMENDED
AutoDowngradeAllowed=YES
1. ActionableScore
* Raw conservative score: 0
* Conservative score: 0
* Raw paranoid score: 0
* Paranoid score: 0
* No floor or cap applied.
* Final recommended bucket: **Ordinary Moderate**::
2. Signal breakdown
* +1 Memory layout invariant restoration. The change keeps the encoded hardware EOP ring size consistent with the actual byte size without relying on subtraction after logarithm calculation.
* -1 Highly constrained theoretical arithmetic defect. The commit positively states that the ring cannot be smaller than 4096 bytes. At that size, the old expression cannot underflow.
* No corruption bonus. No reachable OOB access, DMA overwrite, stale pointer, UAF, or active-object corruption is established.
* No crash or availability point. The patch provides no observed GPU hang, kernel crash, or host-wide failure.
* No local-unprivileged point. A process may have KFD access, but the evidence does not show that it can supply the undersized ring needed to reach the underflow.
* No C or I signal. The earlier CVSS interpretation that the GPU might access beyond the ring depends on first bypassing an invariant that the supplied evidence says cannot be violated.
* No paranoid bonus. Treating a hypothetical invariant bypass as an established hardware OOB primitive would require unsupported additional mechanics.
* No repeated release, refcount mutation, race, or lifetime violation exists.
3. Reachability analysis
The relevant path programs AMD KFD queue state and therefore requires compatible AMD GPU hardware and KFD use. The complete privilege boundary is not shown, so HostAdminRequired remains UNKNOWN rather than assuming either host administration or ordinary-user reachability.
Although KFD is commonly exposed to authorized graphics or compute users, the supplied evidence states that the EOP ring size cannot be below 4096 bytes. The attacker therefore cannot reach the arithmetic boundary through the supported queue configuration described here. No namespace capability or namespace-scoped trigger is established. There is no network vector, race, prior privileged setup evidence, or demonstrated method for bypassing the minimum-size invariant.
4. Primitive and severity interpretation
The exact defect is a theoretically unsafe integer expression, not an established memory-corruption primitive. If `order_base_2()` returned zero, subtracting one could wrap and cause the hardware field to encode a larger ring. However, the documented minimum ring size prevents that input under normal supported operation.
This is neither active structured corruption nor fixed stale storage. There is no UAF and no repeated lifetime operation. A GPU access beyond the allocation is speculative because neither an undersized allocation nor such an access is demonstrated.
PrimitiveClass is NONE because no meaningful reachable corruption, ownership, lifetime, or authorization primitive is established. ImportantCandidate is NO because the evidence does not support Important-grade leverage. AutoDowngradeAllowed is YES because the remaining concern is a defensive arithmetic correction with an asserted invariant preventing practical triggering.
5. One-sentence report phrase
The old AMD KFD EOP ring size expression was theoretically capable of integer underflow, but the documented 4096 byte minimum prevents the boundary in supported operation and no reachable corruption or crash is established.
6. Manual review recommendation
MANUAL CHECK RECOMMENDED
Confirm all assignments and validation paths for `eop_ring_buffer_size`, because an undocumented path allowing a value below 8 bytes would materially change the assessment and require review of possible GPU accesses beyond the allocated ring.
7. Call-site confidence
Call-site confidence: medium
======================================================================
UPSTREAM PATCH SUMMARY
======================================================================
Patch: drm/amdkfd: Avoid integer underflow in EOP ring size calculation.
Commit: 287a34c4d712e0bdb67751e21316d9c8d75a528a
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=287a34c4d712e0bdb67751e21316d9c8d75a528a
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
order_base_2(q->eop_ring_buffer_size / 4) - 1
But order_base_2 can in theory return 0, so this could underflow
(although in practice the ring buffer size cannot be less than 4096).
Change this to
order_base_2(q->eop_ring_buffer_size / 8)
using properties of logarithms.
Also add to the above comment to make the mathematics more clear.
Reviewed-by: Kent Russell <[email protected]>
Signed-off-by: David Francis <[email protected]>
Signed-off-by: Alex Deucher <[email protected]>
(cherry picked from commit f0f43fc )
Cc: [email protected]
Signed-off-by: Greg Kroah-Hartman <[email protected]>
Changed files:
drivers/gpu/drm/amd/amdkfd/kfd_mqd_manager_v9.c
drivers/gpu/drm/amd/amdkfd/kfd_mqd_manager_vi.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=287a34c4d712e0bdb67751e21316d9c8d75a528a
======================================================================
DETAILED REPORT METHODOLOGY
======================================================================
The original Linux kernel CVE announcement for CVE-2026-98177 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98177
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:L
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: 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: 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 [email protected] (and both
send reply to CVE record itself too and see "reply" button below for howto reply).
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