[CVE-2026-46220][MODERATE REGULAR] drm/amdgpu/sdma4: replace BUG_ON with WARN_ON in fence emission

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

CVE: CVE-2026-46220
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: drm/amdgpu/sdma4: replace BUG_ON with WARN_ON in fence emission
Commit: 4f7ca00fa91daf0795ec6b3b130c5ebba1f155fe
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=4f7ca00fa91daf0795ec6b3b130c5ebba1f155fe
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-46220
Analysis date: Sat, 01 Aug 2026 10:06:48 -0400
ActionableScore: 4
ActionableScore lower bound: unknown
Actionable bucket: Borderline Moderate / manual review recommended
Manual review required: YES

Summary:
A reachable `BUG_ON` in AMDGPU SDMA v4 fence emission can be triggered by crafted local `DRM_IOCTL_AMDGPU_CS` submissions, allowing an unprivileged user with DRM device access to panic the kernel.

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

The original Linux kernel CVE announcement for CVE-2026-46220 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-46220

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-2026-46220	MODERATE	CHECK WITH IMPACT FROM ORIG NN MODERATE	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-617;*CWE-20;CWE-754;**CWE-400;BEST CVSS score: '5.5';DESCR 'A reachable BUG_ON in the AMDGPU SDMA v4 fence emission path can be triggered from userspace through crafted DRM_IOCTL_AMDGPU_CS submissions. The assertion checks that the fence writeback address is dword aligned, but reaching BUG_ON from an ioctl path causes a fatal kernel panic in a scheduler worker thread. For the CVSS the PR:L means a local unprivileged user or process with access to the AMDGPU DRM device is sufficient, while administrative privileges are not required. The issue is not network reachable and requires local code execution on a system with the affected AMDGPU driver and accessible DRM device nodes. Impact is denial of service via kernel crash. No concrete information disclosure, integrity impact, UAF, OOB write, or privilege escalation primitive is supported by the shown patch context.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Borderline Moderate / manual review recommended (with actual score 4)  SKIP CVE-2026-46220  SKIP No affected files built, so skip this CVE NO  - - unknown 	MAYBE	OOB DANGER SIMPLEFIX KERNEL_PANIC_PLUS_UAF HARDWARE  DECREASED_TO_MODERATE_REGULAR_FROM_MODERATE7_BASED_ON_GUESSCVSS_AND_CIANNH	-	-	checked

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ACTIONABLESCORE ANALYSIS
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ActionableScore=4

## 1. ActionableScore

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

## 2. Signal breakdown

Triggered signals:

* Local unprivileged trigger: +1
  The commit explicitly says crafted `DRM_IOCTL_AMDGPU_CS` submissions from unprivileged userspace can reach the assertion.

* Reliable kernel crash / strong DoS: +1
  `BUG_ON(addr & 0x3)` causes a fatal kernel panic when the misaligned fence address reaches SDMA fence emission.

* Availability impact realistic: +1
  This is not only a warning or soft failure. The described result is a host kernel panic in a scheduler worker thread.

* Broad/common deployed exposure: +1
  AMDGPU DRM is a common graphics stack on affected AMD systems, and DRM render/card device nodes are commonly reachable by local desktop or GPU workload users.

Not triggered:

* No remote/network reachability: +0
* No generic memory corruption: +0
* No real lifetime corruption: +0
* No privilege escalation plausible: +0
* No confidentiality or integrity impact: +0
* No GPU high-control API bonus: +0
  The patch shows a reachable assertion panic, but not attacker control over lifetime, reclaim, DMA mappings, callbacks, or memory layout.

## 3. Reachability analysis

A local user or process with access to the affected AMDGPU DRM device can trigger the bug through crafted command submission ioctls. Administrative privileges are not required if the user has normal access to the DRM render/card node, which is common on desktop and GPU compute systems.

Containers only affect reachability if the AMDGPU device node is passed into the container. Without device passthrough, the bug is not reachable from an ordinary container. The issue is not network reachable and requires local code execution on a system using the affected AMDGPU SDMA v4 path.

Call-site confidence: high. The commit message directly identifies `DRM_IOCTL_AMDGPU_CS` as the userspace path and states that the panic is reachable from unprivileged userspace.

## 4. Severity interpretation

This behaves like an actionable local Moderate issue rather than an Important memory-corruption vulnerability. The practical impact is a reliable local denial of service through kernel panic.

There is no evidence in the patch of UAF, OOB write, arbitrary write, type confusion, refcount misuse, stale callback, or privilege escalation. The issue should therefore not be upgraded beyond DoS based only on the presence of a GPU ioctl path.

## 5. One-sentence report phrase

A reachable `BUG_ON` in AMDGPU SDMA v4 fence emission can be triggered by crafted local `DRM_IOCTL_AMDGPU_CS` submissions, allowing an unprivileged user with DRM device access to panic the kernel.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED

Reason: this is a local unprivileged kernel panic through a commonly exposed DRM ioctl path. It is likely DoS-only, but product exposure depends on AMDGPU hardware presence, driver enablement, and DRM device-node access policy.

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

Patch: drm/amdgpu/sdma4: replace BUG_ON with WARN_ON in fence emission
Commit: 4f7ca00fa91daf0795ec6b3b130c5ebba1f155fe
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=4f7ca00fa91daf0795ec6b3b130c5ebba1f155fe

Commit description:

sdma_v4_0_ring_emit_fence() contains two BUG_ON(addr & 0x3) assertions
that verify fence writeback addresses are dword-aligned.  These
assertions can be reached from unprivileged userspace via crafted
DRM_IOCTL_AMDGPU_CS submissions, causing a fatal kernel panic in a
scheduler worker thread.

Replace both BUG_ON() calls with WARN_ON() to log the condition without
crashing the kernel.  A misaligned fence address at this point indicates
a driver bug, but crashing the kernel is never the correct response when
the assertion is reachable from userspace.

The CS IOCTL path is the correct place to filter invalid submissions;
the ring emission callback is too late to do anything about it.

Fixes: 2130f89 ("drm/amdgpu: add SDMA v4.0 implementation (v2)")
Reviewed-by: Christian König <christian.koenig@amd.com>
Signed-off-by: John B. Moore <jbmoore61@gmail.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
(cherry picked from commit b90250b )
Cc: stable@vger.kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  drivers/gpu/drm/amd/amdgpu/sdma_v4_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=4f7ca00fa91daf0795ec6b3b130c5ebba1f155fe

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

The original Linux kernel CVE announcement for CVE-2026-46220 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-46220

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: Not available
  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: 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).