[CVE-2026-63844][LOW] drm/amdgpu/jpeg: set no_user_fence for JPEG v4.0.3 ring [ Upstream

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

CVE: CVE-2026-63844
Priority: LOW
AL-KERNEL base severity: LOW
KPANIC flag: NO
Patch: drm/amdgpu/jpeg: set no_user_fence for JPEG v4.0.3 ring [ Upstream
Commit: b884ff67d62ef514eee9d5f605c03101c8b6bc98
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=b884ff67d62ef514eee9d5f605c03101c8b6bc98
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-63844
Analysis date: Sun, 19 Jul 2026 11:32:19 -0400
ActionableScore: 2
ActionableScore lower bound: unknown
Actionable bucket: Ordinary Moderate / Low-like
Manual review required: NO

Summary:
AMDGPU JPEG v4.0.3 rings did not reject unsupported 64-bit user fence submissions, allowing a local process with DRM render-node access to trigger a GPU fault or device-level denial of service.

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

The original Linux kernel CVE announcement for CVE-2026-63844 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-63844

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-2026-63844	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-20;CWE-754;**CWE-400;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 v4.0.3 command submission allowed user fences on a JPEG ring that does not support 64 bit user fence writes. A local process with access to the DRM render node can submit a CS using a user fence and may trigger a GPU fault, GPU reset, or device level denial of service. For the CVSS the PR:L is used because reliable triggering requires local code execution with access to the DRM GPU interface, but it does not normally require full administrative privileges. The issue is not network reachable and is triggered through the local graphics command submission path. Impact is primarily availability loss and there is no strong evidence of kernel memory corruption, information disclosure, or privilege escalation from this patch context.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate / Low-like (with actual score 2)  SKIP CVE-2026-63844 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

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

ActionableScore=2

## 1. ActionableScore

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

## 2. Signal breakdown

* Local unprivileged trigger: +1
  A local process with access to the DRM render node can plausibly submit an AMDGPU CS using a user fence.

* Availability impact realistic: +1
  The unsupported 64-bit user fence write on the JPEG v4.0.3 ring may cause GPU fault, GPU reset, or device-level DoS.

* No generic memory corruption: +0
  The patch only sets `.no_user_fence = true` to reject unsupported CS submissions. It does not show UAF, OOB write, double-free, refcount misuse, type confusion, arbitrary write, or attacker-controlled memory corruption.

* No LPE signal: +0
  There is no supported privilege-escalation primitive in the patch or commit message.

* No remote reachability: +0
  This is a local DRM/GPU command submission path, not a network-triggerable path.

* No admin penalty: 0
  Full root is not normally required if the user has render-node access, so PR:L is more appropriate than PR:H.

* Call-site confidence: medium
  The patch is small, but AMDGPU ring flags are well-known validation controls for CS submission behavior.

## 3. Reachability analysis

The bug is reachable by a local user or process that can access the AMDGPU DRM render node and submit command streams. Containers may matter if GPU render devices are passed through into the container, because that can expose the same local GPU submission interface to non-host-root workloads. The affected path is hardware and generation specific to AMD JPEG v4.0.3 rings, but it is not a rare debug-only path when such GPUs are present. Realistic exploitation appears limited to GPU/device availability impact.

## 4. Severity interpretation

This behaves like an ordinary Moderate or Low-like local device DoS issue. The theoretical concern is that unsupported user fence writes could put the GPU ring into a bad state, but the patch does not support memory corruption, information disclosure, integrity impact, or privilege escalation. The practical impact is most likely GPU reset or GPU hang rather than host compromise.

## 5. One-sentence report phrase

AMDGPU JPEG v4.0.3 rings did not reject unsupported 64-bit user fence submissions, allowing a local process with DRM render-node access to trigger a GPU fault or device-level denial of service.

## 6. Manual review recommendation

NO MANUAL CHECK NEEDED

This can be auto-closed for urgent triage purposes because the patch is a validation-only device-specific fix with no concrete memory corruption or privilege-escalation primitive shown.

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

Patch: drm/amdgpu/jpeg: set no_user_fence for JPEG v4.0.3 ring [ Upstream
Commit: b884ff67d62ef514eee9d5f605c03101c8b6bc98
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=b884ff67d62ef514eee9d5f605c03101c8b6bc98

Changed files:
  drivers/gpu/drm/amd/amdgpu/jpeg_v4_0_3.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=b884ff67d62ef514eee9d5f605c03101c8b6bc98

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

The original Linux kernel CVE announcement for CVE-2026-63844 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-63844

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: unknown
  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).