[CVE-2026-99146][LOW] drm/i915/dmc: Add sanity check for DMC load address

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

CVE: CVE-2026-99146
Priority: LOW
AL-KERNEL base severity: LOW
KPANIC flag: NO
Patch: drm/i915/dmc: Add sanity check for DMC load address
Commit: ef82b4d5cb4a3fe77c7f99008d78b8c64709e258
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=ef82b4d5cb4a3fe77c7f99008d78b8c64709e258
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-99146
Analysis date: Thu, 29 Oct 2026 00:28:46 -0400
ActionableScore: 0
ActionableScore lower bound: unknown
Actionable bucket: Ordinary Moderate
Manual review required: NO

Summary:
Unchecked DMC firmware load addresses permit privileged malformed firmware to write payload words outside the selected DMC program range, potentially corrupting GPU/display state or causing device denial of service.

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

The original Linux kernel CVE announcement for CVE-2026-99146 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-99146

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-2026-99146	LOW	https://www.kernelcve.org/list/?q=CVE-2026-99146 CHECK WITH IMPACT FROM ORIG NN LOW | AEGIS IMPACT LOW AEGIS_AS=2 LEGACY=LOW RESULT=SAME (final reconciliation agrees; DECISION: both LOW)	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:L/PR:H/UI:N/S:U/C:N/I:L/A:H';*CWE-20;CWE-1284;Other CVSS 'AV:L/AC:L/PR:H/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '5.1';DESCR 'DMC firmware header version 3 supplied an unchecked start MMIO address that was later used to write the firmware payload into GPU MMIO space. A malformed or malicious firmware image could therefore direct sequential payload writes outside the program memory range assigned to the selected DMC and may corrupt GPU or display state or cause a device or system denial of service. For the CVSS the PR:H value is appropriate because reliable exploitation normally requires replacing the locally stored DMC firmware or controlling an equivalent privileged firmware source before driver initialization or reload. The issue is not remotely reachable and there is no demonstrated CPU memory corruption or privilege escalation primitive. The paranoid integrity impact is limited to GPU MMIO state because the unchecked address provides a device register write path but not evidence of arbitrary host memory access. Automated impact decision path. The original SimpleNet classifier selected LOW. The primary LLM estimated paranoid CVSS 5.1 and the production ActionableScore returned 0 with recommendation Ordinary Moderate. The production rules then evaluated CVSS thresholds and ActionableScore thresholds. Recorded rule transitions were CVSS and initial triage stage LOW to MODERATE_KPANIC because the CVSS score, vector or bug class threshold rule was applied. ActionableScore thresholds stage MODERATE_KPANIC to LOW because the ActionableScore threshold rule was applied. The legacy KP specialist has no review artifact for this run. The legacy FD or DH downgrade specialist has no review artifact for this run. Exact triggered rule markers were INCREASED_FROM_LOW_BASED_ON_HIGHCVSSSCORE and DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN4 and DECREASED_TO_LOW_FROM_MODERATE_BASED_ON_ACTIONABLESCORELESSTHAN3. The independent weaker Aegis shadow evaluated CVSS 3.1 and ActionableScore 2 with primitive class CLASS_B and manual review REQUIRED. Its independently reconciled impact was LOW. The shadow agreed with the final production impact and aggregation did not change that impact. The final reported impact is LOW.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate (with actual score 0)	MAYBE	OOB LEAK HARDWARE  INCREASED_FROM_LOW_BASED_ON_HIGHCVSSSCORE DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN4 DECREASED_TO_LOW_FROM_MODERATE_BASED_ON_ACTIONABLESCORELESSTHAN3	-	-	checked

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ACTIONABLESCORE ANALYSIS
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ActionableScore=0
PrimitiveClass=CLASS_B
RealUAF=NO
HostAdminRequired=YES
NamespaceScopedPrivilege=NO
ImportantCandidate=NO
ManualReview=NO
AutoDowngradeAllowed=YES
RequiresHostUID0=UNKNOWN
AuthorizationDecisionBypass=NO
ProtectedResourceImpact=NONE
B4PendingReview=NO
B4PendingConfirmed=NO

1. ActionableScore

* Raw base score: 0.
* Conservative score: 0; no floor or cap applied.
* Raw paranoid score: 0.
* Paranoid score: 0; no separate proof-supported escalation.
* Final recommended bucket: **Ordinary Moderate**::

2. Signal breakdown

* +1 — Concrete constrained device-state overwrite: firmware header v3 controls `start_mmioaddr`, which `dmc_load_program()` uses for sequential payload writes without validating the selected DMC program range.
* +1 — Device/display denial of service is plausible from writes into unintended GPU MMIO state, although a host panic is not demonstrated.
* -2 — Complete practical trigger requires effective host-administrator control over the installed DMC firmware or an equivalent privileged firmware source.
* No additional integrity point: corruption of GPU state is the consequence of the already-counted MMIO write.
* No CPU-memory OOB write, arbitrary host-memory write, UAF, disclosure, privilege escalation, protected victim, or reliable host-wide crash is shown.
* NEW52/B5-R does not apply: there is no retry-accumulated heap OOB write.
* NEW53/B3-PENDING does not apply: no shared or file-backed storage write exists.
* No authorization decision is bypassed; B4-PENDING is inapplicable.

3. Reachability analysis

The malformed firmware is parsed during DMC firmware loading. Supplied evidence supports exploitation through replacement or control of the local firmware source, an effective host-administrator operation. Numeric UID 0 specifically is not established, hence `RequiresHostUID0=UNKNOWN`. No namespace-scoped, render-node, ordinary-user, or remote trigger is shown. Intel GPU hardware and DMC header version 3 are prerequisites, but no separate rarity penalty is applied.

4. Primitive and severity reading

The primitive is an attacker-influenced, sequential GPU MMIO write outside the program-memory range assigned to the selected DMC. It is constrained device-state corruption, classified CLASS_B rather than CLASS_A because no CPU kernel-memory target, cross-authority effect, or stronger exploitation primitive is demonstrated. Likely effects are GPU/display malfunction or denial of service. Host compromise and privilege escalation remain unsupported. Because the full trigger already requires host-administrator-equivalent firmware control and crosses no additional demonstrated boundary, this is not an Important candidate and may be downgraded automatically.

5. One-sentence report phrase

Unchecked DMC firmware load addresses permit privileged malformed firmware to write payload words outside the selected DMC program range, potentially corrupting GPU/display state or causing device denial of service.

6. Manual review advice

NO MANUAL CHECK NEEDED

The concrete write is limited to GPU MMIO state and requires effective host-administrator firmware control, with no additional security boundary crossed.

7. Call-site confidence

Call-site confidence: medium

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

Patch: drm/i915/dmc: Add sanity check for DMC load address
Commit: ef82b4d5cb4a3fe77c7f99008d78b8c64709e258
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=ef82b4d5cb4a3fe77c7f99008d78b8c64709e258

Commit description:

For DMC firmware header version 3, the firmware load address is stored
in dmc_info->start_mmioaddr and later used by dmc_load_program().

Unlike the MMIO address table, the firmware load address is not
validated. Add a sanity check to ensure it is within the valid range.

BSpec: 69671, 68378
Fixes: 3d5928a ("drm/i915/xelpd: Pipe A DMC plugging")
Cc: stable@vger.kernel.org
Assisted-by: Claude-Code:Sonnet-5
Signed-off-by: Dibin Moolakadan Subrahmanian <dibin.moolakadan.subrahmanian@intel.com>
Reviewed-by: Mitul Golani<mitulkumar.ajitkumar.golani@intel.com>
Signed-off-by: Ankit Nautiyal <ankit.k.nautiyal@intel.com>
Link: https://patch.msgid.link/20260922133535.3180973-6-dibin.moolakadan.subrahmanian@intel.com
(cherry picked from commit 5e47ee5c76ca9becde8df4ad5202845b7ffcbc4c)
Signed-off-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  drivers/gpu/drm/i915/display/intel_dmc.c
  drivers/gpu/drm/i915/display/intel_dmc_regs.h

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=ef82b4d5cb4a3fe77c7f99008d78b8c64709e258

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

The original Linux kernel CVE announcement for CVE-2026-99146 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-99146

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:H/UI:N/S:U/C:N/I:N/A:H
  The Best / paranoid CVSS vector: AV:L/AC:L/PR:H/UI:N/S:U/C:N/I:L/A:H
  The Best / paranoid CVSS score: 5.1

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: 0

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).