[CVE-2026-63848][MODERATE REGULAR] drm/amdgpu/jpeg: set no_user_fence for JPEG v2.0 ring [ Upstream

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

CVE: CVE-2026-63848
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: drm/amdgpu/jpeg: set no_user_fence for JPEG v2.0 ring [ Upstream
Commit: f675801889b265634aefd30aa4503fc2b9e6ce1c
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=f675801889b265634aefd30aa4503fc2b9e6ce1c
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-63848
Analysis date: Sun, 19 Jul 2026 11:22:25 -0400
ActionableScore: 4
ActionableScore lower bound: 2
Actionable bucket: Borderline manual review recommended / Ordinary Moderate likely
Manual review required: YES

Summary:
The amdgpu JPEG v2.0 ring accepted CS submissions with user fences despite lacking 64 bit user fence write support, allowing a local GPU user to trigger unsupported fence handling and potentially cause JPEG ring hang, GPU reset, or GPU availability loss.

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ABOUT THIS REPORT
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The original Linux kernel CVE announcement for CVE-2026-63848 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-63848

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
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CVE-2026-63848	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-20;CWE-754;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 'The amdgpu JPEG v2.0 ring could accept CS submissions with user fences even though this ring does not support 64 bit user fence writes. A local process with access to the DRM amdgpu submission interface could trigger unsupported fence handling on the JPEG ring, which may cause job failure, ring hang, GPU reset, or loss of GPU availability. For the CVSS the PR:L is used because reliable triggering requires a local user or process that can submit GPU command streams through the device interface, but does not normally require full administrative privileges. The issue is not network reachable and is not triggered by remote packet traffic. Impact is primarily denial of service against GPU availability. There is no concrete evidence in this patch of kernel memory corruption, information disclosure, or privilege escalation, but the GPU command submission path should be checked to confirm whether unsupported fence writes are fully contained.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Borderline manual review recommended / Ordinary Moderate likely (with actual score 3)  SKIP CVE-2026-63848 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
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ActionableScore=4
ActionableScoreLower=2

## 1. ActionableScore

* Conservative score: 2
* Paranoid score: 4
* Final recommended bucket: **Borderline manual review recommended / Ordinary Moderate likely**

## 2. Signal breakdown

Conservative signals:

* Local unprivileged trigger: +1. A local process with access to the DRM amdgpu submission interface can submit command streams.
* Availability impact realistic: +1. Unsupported user fence handling on the JPEG ring can plausibly cause job failure, ring hang, GPU reset, or loss of GPU availability.

Paranoid additional signals:

* Reliable kernel/device DoS concern: +1. If user fence submissions reliably hang the JPEG ring or force GPU reset, the availability impact becomes more actionable.
* Broad/default/common exposure: +1. amdgpu render nodes are commonly exposed to local desktop or GPU workload users, although this specific path is hardware and ring dependent.

Not counted:

* No generic memory corruption. The patch does not show UAF, OOB write, double free, type confusion, arbitrary write, or stale callback.
* No privilege escalation plausible signal. Unsupported 64-bit user fence writes are rejected by policy after the patch, but no concrete LPE primitive is shown.
* No confidentiality or integrity impact. The evidence supports availability impact only.
* No high-control device API bonus. GPU command submission is rich, but this patch does not show attacker control over memory lifetime, reclaim, callback targets, DMA mappings, or page ownership.

## 3. Reachability analysis

The bug is reachable by a local user or process that can submit CS jobs to the amdgpu DRM interface, typically through a render node or GPU device node. It does not require network reachability and is not triggered by packet input. It also does not normally require full host-root privileges, because DRM render access is often delegated to local graphical or compute users.

Namespaces and containers may matter if GPU device nodes are passed into containers. In that case, a containerized workload with access to the amdgpu device could potentially trigger the same GPU availability issue. The affected path is hardware dependent and limited to JPEG v2.0 ring behavior.

Call-site confidence: medium. The patch itself is small and does not include the CS submission call path, but amdgpu ring function flags are used by common command submission validation paths.

## 4. Severity interpretation

This behaves more like an ordinary Moderate or borderline actionable Moderate issue, not an Important-class vulnerability. The realistic impact is GPU denial of service through unsupported user fence submission. The theoretical concern is that user fence writes interact with GPU command submission and memory-facing device behavior, but the provided patch does not demonstrate host memory corruption, privilege escalation, or information disclosure.

The conservative score stays low because the fix is validation-style and the downstream failure mode is not described as kernel memory corruption. The paranoid score reaches manual-review territory because local GPU submission interfaces are commonly exposed and GPU hangs or resets can be operationally significant.

## 5. One-sentence report phrase

The amdgpu JPEG v2.0 ring accepted CS submissions with user fences despite lacking 64 bit user fence write support, allowing a local GPU user to trigger unsupported fence handling and potentially cause JPEG ring hang, GPU reset, or GPU availability loss.

## 6. Manual review recommendation

MANUAL CHECK RECOMMENDED

Manual review should confirm whether the unsupported user fence write is fully contained to GPU job failure or reset, or whether any platform has a stronger memory corruption or cross-process GPU memory impact.

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

Patch: drm/amdgpu/jpeg: set no_user_fence for JPEG v2.0 ring [ Upstream
Commit: f675801889b265634aefd30aa4503fc2b9e6ce1c
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=f675801889b265634aefd30aa4503fc2b9e6ce1c

Changed files:
  drivers/gpu/drm/amd/amdgpu/jpeg_v2_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=f675801889b265634aefd30aa4503fc2b9e6ce1c

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

The original Linux kernel CVE announcement for CVE-2026-63848 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-63848

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: 4

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).