[CVE-2026-64214][LOW] powerpc/time: Remove redundant preempt_disable|enable() calls from arch_irq_work_raise() [ Upstream

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

CVE: CVE-2026-64214
Priority: LOW
AL-KERNEL base severity: LOW
KPANIC flag: NO
Patch: powerpc/time: Remove redundant preempt_disable|enable() calls from arch_irq_work_raise() [ Upstream
Commit: 51860e423592893cd7bfa7287d99a3aff4dc3a9d
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=51860e423592893cd7bfa7287d99a3aff4dc3a9d
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64214
Analysis date: Fri, 24 Jul 2026 13:06:41 -0400
ActionableScore: 1
ActionableScore lower bound: 0
Actionable bucket: Ordinary Moderate / Low-like
Manual review required: NO

Summary:
A powerpc MCE real-mode path can call `arch_irq_work_raise()` and fault on `preempt_count` access inside `preempt_disable()`, causing a kernel panic, but the issue is not network reachable and has no demonstrated memory corruption or privilege escalation primitive.

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

The original Linux kernel CVE announcement for CVE-2026-64214 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64214

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-2026-64214	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:L/UI:N/S:U/C:N/I:N/A:H';CWE-703;CWE-754;**CWE-476;Other CVSS 'AV:L/AC:H/PR:H/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '4.7';DESCR 'powerpc arch_irq_work_raise can panic when it is invoked from a machine check exception handler running in real mode. The root cause is that preempt_disable can access preempt_count in a context where that access may fault, leading to a bad kernel data access and system crash. For the CVSS the PR:L is used in the paranoid score because a local privileged or semi privileged maintenance context may be able to provoke MCE related recovery paths, but reliable triggering is not expected for ordinary remote attackers. The issue is not network reachable. Impact is denial of service only via kernel panic, with no evidence of UAF, OOB access, information disclosure, or privilege escalation.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate / Low-like (with actual score 1)  SKIP CVE-2026-64214 UNKNOWN SKIP The Fixes patch not applied yet, so unlikely that actual: cc15ff3275694fedc33cd3d53212a43eec7aa0bc YES  NO NO unknown 	MAYBE	DANGER RACE HARDWARE LINUS  DECREASED_TO_MODERATE_REGULAR_FROM_MODERATE7_BASED_ON_GUESSCVSS_AND_CIANNH DECREASED_TO_LOW_FROM_MODERATE_BASED_ON_ACTIONABLESCORELESSTHAN3	-	-	checked

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

ActionableScore=1
ActionableScoreLower=0

## 1. ActionableScore

* Conservative score: 0
* Paranoid score: 1
* Final recommended bucket: **Ordinary Moderate / Low-like**

## 2. Signal breakdown

Paranoid scoring signals:

* Firmware-mediated external influence: +1
  The failing path is reached from powerpc machine check exception handling, which is hardware or firmware mediated rather than normally user-triggered.
* Reliable kernel crash / strong DoS: +1
  The commit shows a concrete Oops and kernel panic caused by accessing preempt_count from real mode.
* Physical-only or rare hardware-only condition: -2
  Realistic triggering depends on MCE handling from real mode, not a normal syscall, network, filesystem, or device userspace API path.
* Availability impact realistic: +0
  Not added separately because the crash impact is already counted as strong DoS.
* Memory corruption / LPE / C/I impact: +0
  The patch does not show UAF, OOB access, double free, type confusion, arbitrary write, information leak, or privilege escalation primitive.

Conservative interpretation is 0 because there is no clear attacker-controlled trigger and the condition is hardware/MCE-specific.

## 3. Reachability analysis

The bug is reachable when `arch_irq_work_raise()` is invoked from an MCE handler running in real mode on powerpc. Ordinary local users are not expected to be able to reliably generate this condition. Remote network attackers cannot trigger this path directly. A privileged maintenance context, firmware, service processor, fault injection setup, or failing hardware could make the path reachable, but that is not the same as a normal local unprivileged or network attack surface.

Namespaces and containers do not materially lower the privilege requirement because the trigger is below normal namespace-visible kernel interfaces. The affected code is architecture-specific and depends on powerpc MCE behavior.

Call-site confidence: high, because the commit message explicitly gives the call path and the patch directly removes the unsafe `preempt_disable()` / `preempt_enable()` calls.

## 4. Severity interpretation

This behaves like an ordinary Moderate or Low-like reliability/security-adjacent DoS issue, not an Important-class vulnerability. The realistic impact is kernel panic under a rare real-mode MCE condition. There is no demonstrated memory corruption primitive, no practical privilege escalation path, and no confidentiality or integrity impact supported by the patch.

Theoretical concern is limited to system availability. Realistic exploitation evidence is weak because triggering depends on machine check handling rather than a normal attacker-controlled interface.

## 5. One-sentence report phrase

A powerpc MCE real-mode path can call `arch_irq_work_raise()` and fault on `preempt_count` access inside `preempt_disable()`, causing a kernel panic, but the issue is not network reachable and has no demonstrated memory corruption or privilege escalation primitive.

## 6. Manual review recommendation

NO MANUAL CHECK NEEDED

The issue is a concrete DoS/panic fix in a rare architecture-specific MCE path, with no UAF, OOB write, information leak, privilege escalation, or broadly reachable attacker-controlled interface shown.

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

Patch: powerpc/time: Remove redundant preempt_disable|enable() calls from arch_irq_work_raise() [ Upstream
Commit: 51860e423592893cd7bfa7287d99a3aff4dc3a9d
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=51860e423592893cd7bfa7287d99a3aff4dc3a9d

Changed files:
  arch/powerpc/kernel/time.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=51860e423592893cd7bfa7287d99a3aff4dc3a9d

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

The original Linux kernel CVE announcement for CVE-2026-64214 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64214

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:H/PR:H/UI:N/S:U/C:N/I:N/A:H
  The Best / paranoid CVSS vector: AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H
  The Best / paranoid CVSS score: 4.7

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: 0
  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).