[CVE-2026-80688][LOW] riscv: drop __init from vec_check_unaligned_access_speed_all_cpus [ Upstream

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

CVE: CVE-2026-80688
Priority: LOW
AL-KERNEL base severity: LOW
KPANIC flag: NO
Patch: riscv: drop __init from vec_check_unaligned_access_speed_all_cpus [ Upstream
Commit: 01bd01b61ad9ea917e5629a7f14f57a8af0543bb
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=01bd01b61ad9ea917e5629a7f14f57a8af0543bb
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-80688
Analysis date: Fri, 28 Aug 2026 04:21:04 -0400
ActionableScore: 2
ActionableScore lower bound: 0
Actionable bucket: Ordinary Moderate / Low-like
Manual review required: YES

Summary:
A RISC-V boot-time kthread could execute `vec_check_unaligned_access_speed_all_cpus()` after `.init.text` was freed by `free_initmem()`, causing an instruction page fault and boot-time kernel DoS under slow SBI probing conditions.

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

The original Linux kernel CVE announcement for CVE-2026-80688 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-80688

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: 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-2026-80688	LOW	CHECK WITH IMPACT FROM ORIG NN NONE	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-672;*CWE-416;*CWE-664;Other CVSS 'AV:L/AC:H/PR:H/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '4.7';DESCR 'A RISC-V boot time kernel thread can continue executing vec_check_unaligned_access_speed_all_cpus after free_initmem() has released the .init.text section because the thread entry function was incorrectly marked __init. If the SBI based unaligned access speed probe is slow, the kthread may fetch instructions from unmapped init memory and trigger an instruction page fault, causing an Oops or kernel panic. For the CVSS the PR:L is used only in the paranoid score to cover environments where a reduced privilege local operator can influence boot configuration or firmware behavior. In the normal case PR:H is more realistic because reliable triggering requires administrative control over the platform, kernel boot path, or SBI behavior. The issue is not network reachable and does not provide a clear information leak or write primitive. Impact is denial of service during boot only. NO MANUAL CHECK REQUIRED COULD BE AUTOCLOSED';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate / Low-like (with actual score 1)  SKIP CVE-2026-80688 UNKNOWN SKIP No affected files built, so skip this CVE NO  - - unknown 	MAYBE	OOB INIT UAF SKIP HARDWARE LINUS 	-	-	checked

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ACTIONABLESCORE ANALYSIS
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ActionableScore=2
ActionableScoreLower=0

## 1. ActionableScore

* Conservative score: 0
* Paranoid score: 2
* Final recommended bucket: **Ordinary Moderate / Low-like**

## 2. Signal breakdown

Conservative signals:

* Real lifetime corruption: +1. A kthread entry function was placed in `.init.text` and could remain executing after `free_initmem()` released that memory.
* Reliable kernel crash / strong DoS: +1. The commit includes a concrete instruction page fault / Oops trace from executing unmapped init text.
* Requires admin/root/platform control in typical deployments: -2. Reliable triggering appears to require control over boot timing, kernel configuration, platform firmware/SBI behavior, or debug instrumentation.
* Rare AND difficult-to-reach subsystem/configuration: -1. This is RISC-V specific and depends on slow SBI probing during early boot.

Paranoid adjustment:

* Firmware-mediated external influence: +1. If SBI or platform firmware behavior can delay the probe, it can influence the race window.
* Hard or unreliable race / special timing required: -1. The bug depends on the kthread still running after init memory is freed.

Not awarded:

* No local unprivileged trigger.
* No remote/network reachability.
* No privilege escalation plausibility.
* No generic attacker-controlled memory corruption primitive.
* No confidentiality or integrity impact.

Call-site confidence: high. The relevant kthread entry function and the `__init` removal are directly visible in the patch.

## 3. Reachability analysis

The bug is reached during RISC-V boot when `vec_check_unaligned_access_speed_all_cpus()` runs as a kernel thread while still marked `__init`. If the SBI based probing is slow enough, `free_initmem()` can unmap `.init.text` before the kthread finishes, causing an instruction fetch fault.

This is not reachable from the network and is not a normal local user interface. A regular unprivileged user cannot reliably trigger it after the system has booted. Containers and namespaces do not materially lower the privilege requirement because the affected path is early boot and platform/SBI dependent.

## 4. Severity interpretation

This behaves like a boot-time reliability bug with DoS impact, not like an Important-class kernel vulnerability. The theoretical issue is a lifetime violation of init text used by a still-running kthread, but the observed primitive is an instruction page fault, not attacker-controlled reuse, write-after-free, type confusion, callback control, or privilege escalation.

The practical severity is ordinary Moderate / Low-like. It should not be treated as Actionable Moderate or Important without external evidence of attacker-controlled triggering beyond platform or firmware timing influence.

## 5. One-sentence report phrase

A RISC-V boot-time kthread could execute `vec_check_unaligned_access_speed_all_cpus()` after `.init.text` was freed by `free_initmem()`, causing an instruction page fault and boot-time kernel DoS under slow SBI probing conditions.

## 6. Manual review recommendation

NO MANUAL CHECK NEEDED.

NO MANUAL CHECK REQUIRED COULD BE AUTOCLOSED. The issue is boot-time only, not network reachable, not locally triggerable by an unprivileged user, and shows no supported confidentiality, integrity, or privilege-escalation primitive.

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

Patch: riscv: drop __init from vec_check_unaligned_access_speed_all_cpus [ Upstream
Commit: 01bd01b61ad9ea917e5629a7f14f57a8af0543bb
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=01bd01b61ad9ea917e5629a7f14f57a8af0543bb

Changed files:
  arch/riscv/kernel/unaligned_access_speed.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=01bd01b61ad9ea917e5629a7f14f57a8af0543bb

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

The original Linux kernel CVE announcement for CVE-2026-80688 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-80688

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: 2

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).