[CVE-2026-63840][LOW] drm/amdgpu/jpeg: set no_user_fence for JPEG v5.3.0 ring [ Upstream

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

CVE: CVE-2026-63840
Priority: LOW
AL-KERNEL base severity: LOW
KPANIC flag: NO
Patch: drm/amdgpu/jpeg: set no_user_fence for JPEG v5.3.0 ring [ Upstream
Commit: 46ad73aec27d020f103b4262e4da2d2c22f54799
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=46ad73aec27d020f103b4262e4da2d2c22f54799
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-63840
Analysis date: Sun, 19 Jul 2026 11:20:49 -0400
ActionableScore: 2
ActionableScore lower bound: 1
Actionable bucket: Ordinary Moderate / Low-like
Manual review required: NO

Summary:
AMDGPU JPEG v5.3.0 accepted user fences on a ring that does not support 64 bit user fence writes, allowing a local process with GPU device access to trigger unsupported command submission behavior and possible GPU denial of service.

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

The original Linux kernel CVE announcement for CVE-2026-63840 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-63840

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.

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AL-KERNEL CLASSIFICATION RESULT
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CVE-2026-63840	LOW	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-754;*CWE-20;CWE-693;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 JPEG v5.3.0 command submission allowed user fences even though this JPEG ring does not support 64 bit user fence writes. A local process with access to the AMDGPU render device could submit a JPEG CS with a user fence and drive the ring into unsupported fence handling. For the CVSS the PR:L is used for the paranoid score because triggering requires local code execution with access to the GPU device node, but not full administrator privileges in common desktop or compute deployments. The issue is not network reachable. Impact is primarily denial of service through failed submissions, possible GPU ring fault, or GPU reset rather than direct confidentiality or integrity compromise.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate / Low-like (with actual score 2)  SKIP CVE-2026-63840 UNKNOWN SKIP No affected files built, so skip this CVE NO  - - unknown 	MAYBE	SIMPLEFIX HARDWARE  INCREASED_FROM_LOW_BASED_ON_HIGHCVSSSCORE DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN5 DECREASED_TO_LOW_FROM_MODERATE_BASED_ON_ACTIONABLESCORELESSTHAN3	-	-	checked

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ACTIONABLESCORE ANALYSIS
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ActionableScore=2
ActionableScoreLower=1

## 1. ActionableScore

* Conservative score: 1
* Paranoid score: 2
* Final recommended bucket: **Ordinary Moderate / Low-like**

## 2. Signal breakdown

* Local unprivileged trigger: +1
  A local process with access to the AMDGPU DRM render node may be able to submit a JPEG command stream with a user fence.

* Availability impact realistic: +1 only in paranoid score
  Unsupported user fence handling on the JPEG ring may plausibly cause failed submissions, ring fault, GPU reset, or local graphics/compute disruption. The patch does not show a reliable kernel panic or host-wide crash.

* No memory corruption signal: +0
  The patch only sets `.no_user_fence = true` for the JPEG v5.3.0 ring. It does not show UAF, OOB write, double free, refcount misuse, arbitrary write, or page ownership corruption.

* No LPE signal: +0
  There is no demonstrated reclaim primitive, overwrite target, callback control, type confusion, or privilege boundary bypass.

* Device-specific validation/capability mismatch: limits priority
  This is a GPU ring capability validation fix, not a generic kernel memory lifetime or ownership corruption issue.

Call-site confidence: medium. The patch is small and local, and the commit message clearly states the intended behavior, but no deeper call-site trace or crash log is provided.

## 3. Reachability analysis

The likely trigger is local command submission through AMDGPU DRM interfaces on systems with affected JPEG v5.3.0 hardware. This does not appear network reachable. In common desktop or compute deployments, render node access may be available to local non-root users through device permissions or group membership, so PR:L is a reasonable practical assumption. Containers may matter only if the GPU device node is delegated into the container. The affected path is hardware-specific and depends on AMDGPU JPEG v5.3.0 support.

## 4. Severity interpretation

This behaves like an ordinary Moderate or Low-like device validation issue. The realistic impact is local denial of service against the GPU ring or graphics/compute stack. Theoretical impact beyond DoS is not supported by the patch, because the change rejects an unsupported user fence mode and does not expose a concrete memory corruption primitive.

## 5. One-sentence report phrase

AMDGPU JPEG v5.3.0 accepted user fences on a ring that does not support 64 bit user fence writes, allowing a local process with GPU device access to trigger unsupported command submission behavior and possible GPU denial of service.

## 6. Manual review recommendation

NO MANUAL CHECK NEEDED

Reason: no memory corruption, no privilege escalation path, no remote reachability, and the patch is a narrow validation fix for a device-specific unsupported fence feature.

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

Patch: drm/amdgpu/jpeg: set no_user_fence for JPEG v5.3.0 ring [ Upstream
Commit: 46ad73aec27d020f103b4262e4da2d2c22f54799
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=46ad73aec27d020f103b4262e4da2d2c22f54799

Changed files:
  drivers/gpu/drm/amd/amdgpu/jpeg_v5_3_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=46ad73aec27d020f103b4262e4da2d2c22f54799

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

The original Linux kernel CVE announcement for CVE-2026-63840 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-63840

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: 1
  Paranoid ActionableScore: 2

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).