[CVE-2026-99090][LOW] drm/amdgpu: serialize vblank counter reads against GPU reset

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

CVE: CVE-2026-99090
Priority: LOW
AL-KERNEL base severity: LOW
KPANIC flag: NO
Patch: drm/amdgpu: serialize vblank counter reads against GPU reset
Commit: 037796d9ca1da97978deaefd88ca5649f6cb69f5
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=037796d9ca1da97978deaefd88ca5649f6cb69f5
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-99090
Analysis date: Mon, 26 Oct 2026 22:29:29 -0400
ActionableScore: 0
ActionableScore lower bound: unknown
Actionable bucket: Ordinary Moderate
Manual review required: NO

Summary:
An unsynchronized AMDGPU vblank hardware read during GPU reset can trigger a lockdep warning, with no demonstrated memory corruption, authorization bypass, or reliable crash.

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

The original Linux kernel CVE announcement for CVE-2026-99090 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-99090

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-2026-99090	LOW	https://www.kernelcve.org/list/?q=CVE-2026-99090 CHECK WITH IMPACT FROM ORIG NN LOW | AEGIS IMPACT LOW AEGIS_AS=0 LEGACY=LOW RESULT=SAME (final reconciliation agrees; DECISION: both 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:N/I:N/A:H';CWE-362;CWE-667;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:L';BEST CVSS score: '4.7';DESCR 'The amdgpu vblank counter callback can read display registers and scanout position while GPU reset holds reset_domain sem for writing. This unsynchronized hardware access triggers a lockdep assertion and TAINT_WARN when lockdep is enabled. For the CVSS the PR:L value reflects that reliable triggering requires a local process with access to the DRM device and the ability to exercise GPU activity while a reset occurs. AC:H reflects the required timing overlap with GPU recovery. No UAF, OOB access, information leak, or write primitive is established. The demonstrated impact is a kernel warning with possible limited display availability degradation, while a GPU or display hang remains a conservative worst case rather than a proven result. Automated impact decision path. The original SimpleNet classifier selected LOW. The primary LLM estimated paranoid CVSS 4.7 and the production ActionableScore returned 0 with recommendation Ordinary Moderate. The production rules then evaluated CVSS thresholds and ActionableScore thresholds. No severity changing production threshold or specialist override was recorded. The legacy KP specialist has no review artifact for this run. The legacy FD or DH downgrade specialist has no review artifact for this run. The independent weaker Aegis shadow evaluated CVSS 0.0 and ActionableScore 0 with primitive class CLASS_C and manual review REQUIRED. Its independently reconciled impact was LOW. The shadow agreed with the final production impact and aggregation did not change that impact. The final reported impact is LOW.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate (with actual score 0)	MAYBE	LOCK WARNONLY SIMPLEFIX HARDWARE 	-	-	checked

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

ActionableScore=0
PrimitiveClass=NONE
RealUAF=NO
HostAdminRequired=UNKNOWN
NamespaceScopedPrivilege=UNKNOWN
ImportantCandidate=NO
ManualReview=NO
AutoDowngradeAllowed=YES
RequiresHostUID0=UNKNOWN
AuthorizationDecisionBypass=NO
ProtectedResourceImpact=NONE
B4PendingReview=NO
B4PendingConfirmed=NO

1. ActionableScore

* Raw base score: 0.
* Conservative score: 0; no floor or cap applies.
* Raw paranoid score: 0.
* Paranoid score: 0; a GPU/display hang is not established strongly enough to score.
* Final recommended bucket: **Ordinary Moderate**::

2. Signal breakdown

* +0 warning-only synchronization defect: the callback accesses display hardware without holding `reset_domain->sem`, triggering `lockdep_assert_held()` and `TAINT_WARN` during reset.
* +0 availability: neither a kernel crash nor a GPU/display hang is demonstrated. The commit specifically addresses unsafe reset-time access and a warning.
* No UAF, OOB access/write, stale lifetime operation, shared-backing write, active-state corruption, authorization bypass, or protected-resource effect is shown.
* No retry-accumulated OOB mechanics or later consumption of corrupted structured state exist; B5-R does not apply.
* No negative timing penalty was applied: overlap with GPU recovery is required, but there was no positive score to reduce and the race is not proved to be uniquely difficult.

3. Reachability analysis

A local process with access to the DRM device may exercise vblank-related activity while GPU recovery occurs, but the supplied evidence does not establish which actor can induce the complete reset overlap. It does not prove ordinary-user, DRM-master, compositor, delegated-service, or host-administrator-only reachability. No namespace capability path, special rare hardware requirement, or separate privileged setup is established.

4. Primitive and severity reading

The defect is a missing read-side reset semaphore around hardware register and scanout-position reads. The shown result is a lockdep assertion and kernel taint, not memory corruption or a reliable host-wide DoS. The fix either acquires the semaphore or returns the cached software vblank count. A display hang remains speculative. Consequently, the issue has no Class A/B/C security primitive, is not an Important candidate, and can be auto-downgraded.

5. One-sentence report phrase

An unsynchronized AMDGPU vblank hardware read during GPU reset can trigger a lockdep warning, with no demonstrated memory corruption, authorization bypass, or reliable crash.

6. Manual review advice

NO MANUAL CHECK NEEDED

The patch-supported effect is warning-only and exposes no unresolved corruption or trust-boundary primitive.

7. Call-site confidence

Call-site confidence: high

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

Patch: drm/amdgpu: serialize vblank counter reads against GPU reset
Commit: 037796d9ca1da97978deaefd88ca5649f6cb69f5
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=037796d9ca1da97978deaefd88ca5649f6cb69f5

Commit description:

The vblank counter callback reads display registers and scanout
position without holding reset_domain->sem. During GPU recovery,
display commit work can call the callback while reset owns the
semaphore for writing. The hardware access then triggers the
lockdep_assert_held() in amdgpu_device_skip_hw_access() and sets
TAINT_WARN when lockdep is enabled.

Try to acquire the reset semaphore for reading before accessing the
hardware, and hold it across the counter and scanout-position reads.
If reset is already in progress, return DRM's cached software vblank
count instead. This avoids blocking behind reset and avoids accessing
display hardware while it is being reset.

The cached count is less accurate than the hardware count, but is
used only when reset prevents a safe hardware read. This addresses
the reset-time warning from this vblank path; it does not suppress or
fix unrelated lockdep warnings.

Cc: Christian König <christian.koenig@amd.com>
Cc: Alex Deucher <alexander.deucher@amd.com>
Cc: Harry Wentland <harry.wentland@amd.com>
Cc: Sunpeng Li <sunpeng.li@amd.com>
Signed-off-by: Vitaly Prosyak <vitaly.prosyak@amd.com>
Reviewed-by: Sunpeng Li <sunpeng.li@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
(cherry picked from commit 51a4359 )
Cc: stable@vger.kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  drivers/gpu/drm/amd/amdgpu/amdgpu_kms.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=037796d9ca1da97978deaefd88ca5649f6cb69f5

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

The original Linux kernel CVE announcement for CVE-2026-99090 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-99090

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:N/I:N/A:H
  The Best / paranoid CVSS score: 4.7

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: 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).