[CVE-2026-63854][MODERATE REGULAR] drm/amdgpu/vcn: set no_user_fence for VCN v3.0 enc/dec rings [ Upstream

[CVE-2026-63854][MODERATE REGULAR] drm/amdgpu/vcn: set no_user_fence for VCN v3.0 enc/dec rings [ Upstream

[AL-KERNEL]

CVE: CVE-2026-63854
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: drm/amdgpu/vcn: set no_user_fence for VCN v3.0 enc/dec rings [ Upstream
Commit: e74fc9c72c1ba78d0de0b849f5929c3b39a8e20c
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=e74fc9c72c1ba78d0de0b849f5929c3b39a8e20c
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-63854
Analysis date: Sun, 19 Jul 2026 11:32:29 -0400
ActionableScore: 3
ActionableScore lower bound: 2
Actionable bucket: Borderline Moderate / manual review recommended
Manual review required: YES

Summary:
AMDGPU VCN v3.0 encoder and decoder rings accepted user fence submissions despite not supporting 64 bit user fence writes, allowing a local GPU client to trigger incorrect fence handling and likely GPU denial of service, without evidence of kernel memory corruption or privilege escalation.

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

The original Linux kernel CVE announcement for CVE-2026-63854 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-63854

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.

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

CVE-2026-63854	MODERATE	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:U/C:N/I:N/A:H';CWE-693;CWE-754;CWE-667;Other CVSS 'AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:L';BEST CVSS score: '5.5';DESCR 'AMDGPU VCN v3.0 encoder and decoder rings could accept command submissions with user fences even though these rings do not support 64 bit user fence writes. A local process with access to the AMDGPU DRM device or render node could submit such a command and trigger incorrect fence handling on the affected VCN rings. For the CVSS the PR:L is used because reliable triggering requires a local user context with access to the GPU submission interface, not full administrative privileges. The issue is not directly network reachable. The most likely impact is denial of service through GPU job failure, ring timeout, or GPU reset. No clear kernel memory corruption primitive is visible from the patch, so confidentiality and integrity are not raised in the base score.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Borderline Moderate / manual review recommended (with actual score 3)  SKIP CVE-2026-63854 UNKNOWN SKIP No affected files built, so skip this CVE NO  - - unknown 	MAYBE	SIMPLEFIX HARDWARE  INCREASED_FROM_LOW_BASED_ON_REQUIREMANUALCHECK DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN5	-	-	checked

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

ActionableScore=3
ActionableScoreLower=2

## 1. ActionableScore

* Conservative score: 2
* Paranoid score: 3
* Final recommended bucket: **Borderline Moderate / manual review recommended**

## 2. Signal breakdown

Triggered signals:

* Local unprivileged trigger: +1
  A local process with access to the AMDGPU DRM render node can likely submit command streams to the affected VCN rings.

* Availability impact realistic: +1
  Unsupported user fence submissions may cause incorrect fence handling, command submission failure, ring timeout, GPU reset, or graphics/media stack disruption.

Paranoid-only signal:

* Device command submission state corruption concern: +1
  The bug involves accepting an unsupported GPU command submission feature on hardware rings. The patch does not show a kernel memory corruption primitive, but hardware-specific fence behavior deserves limited manual scrutiny.

Not awarded:

* Remote reachable: +0
  No network path is involved.

* Generic memory corruption: +0
  The patch only sets `.no_user_fence = true` and does not show UAF, OOB write, double-free, refcount misuse, arbitrary write, or type confusion.

* Privilege escalation plausible: +0
  No concrete LPE primitive is visible.

* High-control kernel data-plane API: +0
  DRM command submission is a rich device API, but the patch does not show attacker control over kernel memory layout, object lifetime, callbacks, refcounts, DMA mappings, or page ownership.

Subtractions:

* Hardware-specific affected path: -1 in the conservative interpretation
  The issue is limited to AMDGPU VCN v3.0 encoder and decoder rings, not a broad kernel subsystem path.

## 3. Reachability analysis

The likely trigger is a local user process that can access the AMDGPU DRM device or render node and submit VCN encoder or decoder command streams with user fences. This does not normally require full root privileges on desktop or GPU-enabled compute systems where render nodes are exposed to users, so PR:L is a reasonable CVSS interpretation.

The issue is not directly network reachable. Containers may matter if GPU devices are passed through or exposed into the container, but without GPU device access the bug is not reachable. The path is hardware and driver specific, requiring AMDGPU hardware with VCN v3.0 support and affected ring configuration.

## 4. Severity interpretation

This behaves more like an ordinary to borderline Moderate issue than an Important-class vulnerability. The realistic impact is local denial of service against the GPU/media stack, potentially including ring timeout or GPU reset. The patch does not support treating this as kernel memory corruption or privilege escalation.

The paranoid score is slightly higher because unsupported user fence writes are hardware-specific and command-submission-related, so manual confirmation of the actual failure mode is useful. However, the evidence does not justify Actionable Moderate or Important handling.

## 5. One-sentence report phrase

AMDGPU VCN v3.0 encoder and decoder rings accepted user fence submissions despite not supporting 64 bit user fence writes, allowing a local GPU client to trigger incorrect fence handling and likely GPU denial of service, without evidence of kernel memory corruption or privilege escalation.

## 6. Manual review recommendation

MANUAL CHECK RECOMMENDED

Manual review is recommended because DRM render nodes are commonly reachable by local users and the exact hardware behavior of unsupported 64 bit user fence writes should be confirmed. This does not currently look like an Important candidate and should not be escalated without evidence of kernel memory corruption, page ownership violation, or privilege escalation.

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

Patch: drm/amdgpu/vcn: set no_user_fence for VCN v3.0 enc/dec rings [ Upstream
Commit: e74fc9c72c1ba78d0de0b849f5929c3b39a8e20c
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=e74fc9c72c1ba78d0de0b849f5929c3b39a8e20c

Changed files:
  drivers/gpu/drm/amd/amdgpu/vcn_v3_0.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=e74fc9c72c1ba78d0de0b849f5929c3b39a8e20c

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

The original Linux kernel CVE announcement for CVE-2026-63854 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-63854

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:N/I:N/A:L
  The Best / paranoid CVSS vector: AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
  The Best / paranoid CVSS score: 5.5

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: 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).