[CVE-2026-64183][LOW] efi: Allocate runtime workqueue before ACPI init

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

CVE: CVE-2026-64183
Priority: LOW
AL-KERNEL base severity: LOW
KPANIC flag: NO
Patch: efi: Allocate runtime workqueue before ACPI init
Commit: 29cd94e678fcb3c4fd0f359deeac6d61334323fc
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=29cd94e678fcb3c4fd0f359deeac6d61334323fc
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64183
Analysis date: Sun, 19 Jul 2026 13:33:17 -0400
ActionableScore: 1
ActionableScore lower bound: unknown
Actionable bucket: Ordinary Moderate / Low-like
Manual review required: NO

Summary:
No one-sentence report phrase was found.

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

The original Linux kernel CVE announcement for CVE-2026-64183 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64183

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-2026-64183	LOW	CHECK WITH IMPACT FROM ORIG NN MODERATE	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:H/PR:H/UI:N/S:U/C:N/I:N/A:H';**CWE-476;CWE-665;CWE-754;BEST CVSS score: '4.1';DESCR 'An EFI runtime workqueue initialization ordering bug can allow early ACPI PRM EFI runtime calls to run before efi_rts_wq is allocated. This can result in a NULL pointer dereference during boot or early subsystem initialization, causing a kernel crash or failed boot. For the CVSS the PR:H is used because reliable attacker controlled triggering normally requires control over firmware, ACPI PRM tables, or privileged boot configuration rather than access by an ordinary local user. The issue is not network reachable and is not triggered by packet traffic or a normal remote service interface. Impact is denial of service only, with no supported evidence of information disclosure, memory corruption beyond NULL dereference, or privilege escalation.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate / Low-like (with actual score 1)	YES	NULLPTR INIT DEBUGFS LINUS  DECREASED_TO_MODERATE_REGULAR_FROM_MODERATE7_BASED_ON_GUESSCVSS DECREASED_TO_LOW_FROM_MODERATE_BASED_ON_ACTIONABLESCORELESSTHAN3	YES	NO	checked

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ACTIONABLESCORE ANALYSIS
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ActionableScore=1

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

2. Signal breakdown
* Firmware-mediated external influence: +1. The trigger depends on early ACPI PRM or EFI runtime behavior coming from firmware or platform tables.
* Reliable kernel crash / strong DoS: +1. The described failure is a NULL pointer dereference before the EFI runtime workqueue exists, potentially causing boot or early-init failure.
* Availability impact realistic: +1. Failed boot or early subsystem crash is a real availability impact on affected platforms.
* Requires admin/root/firmware/boot configuration control: -2. A normal local user cannot reliably shape ACPI PRM tables, firmware behavior, or boot-time EFI runtime ordering.
* Rare/difficult-to-reach configuration: -1. ACPI PRM plus this exact initcall ordering is platform/configuration dependent rather than broadly user-triggerable.

3. Reachability analysis
The bug is triggered during boot or early subsystem initialization when ACPI PRM invokes EFI runtime services before the runtime workqueue is allocated. Realistic attacker control generally requires firmware influence, malicious or buggy ACPI PRM tables, or privileged control over boot/platform configuration. It is not network reachable, not reachable through a normal syscall by an unprivileged local user, and namespaces or containers do not materially reduce the privilege requirement.

4. Severity interpretation
This behaves like a platform-dependent DoS or boot reliability issue, not an Important-class kernel vulnerability. The concrete primitive is a NULL pointer dereference, with no evidence of UAF, OOB write, stale callback, object reuse, information disclosure, integrity corruption, or privilege escalation. Theoretical impact is limited to availability unless an attacker already controls firmware or boot configuration.

5. One-sentence report phrase
An EFI runtime workqueue init ordering bug can allow early ACPI PRM EFI runtime calls to hit a NULL pointer dereference during boot or early subsystem initialization, causing a local platform-dependent DoS but not a realistic unprivileged or remote attack.

6. Manual review recommendation
NO MANUAL CHECK NEEDED. The patch and commit support only a NULL dereference availability issue in an early firmware-mediated path, with high privilege or platform-control requirements and no memory corruption primitive beyond the NULL dereference.

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

Patch: efi: Allocate runtime workqueue before ACPI init
Commit: 29cd94e678fcb3c4fd0f359deeac6d61334323fc
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=29cd94e678fcb3c4fd0f359deeac6d61334323fc

Commit description:

Since commit

  5894cf5 ("acpi/prmt: Use EFI runtime sandbox to invoke PRM handlers")

ACPI PRM calls are delegated to a workqueue which runs in a kernel
thread, making it easier to detect and mitigate faulting memory accesses
performed by the firmware.

Rafael reports that such PRM accesses may occur before efisubsys_init()
executes, which is where the workqueue is allocated, leading to NULL
pointer dereferences. Since acpi_init() [which triggers the early PRM
accesses] executes as a subsys_initcall() as well, and has its own
dependencies that may be sensitive to initcall ordering, deferring
acpi_init() is not an option.

So instead, split off the workqueue allocation into its own postcore
initcall, as this is the only missing piece to allow EFI runtime calls
to be made. This ensures that EFI runtime call (including PRM calls) are
accessible to all code running at subsys_initcall() level.

Cc: <stable@vger.kernel.org>
Fixes: 5894cf5 ("acpi/prmt: Use EFI runtime sandbox to invoke PRM handlers")
Reviewed-by: Rafael J. Wysocki (Intel) <rafael@kernel.org>
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  drivers/firmware/efi/efi.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=29cd94e678fcb3c4fd0f359deeac6d61334323fc

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

The original Linux kernel CVE announcement for CVE-2026-64183 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64183

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:H/PR:H/UI:N/S:U/C:N/I:N/A:H
  The Best / paranoid CVSS score: 4.1

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: 1

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).