[CVE-2026-90212][MODERATE REGULAR] arm64/efi: Avoid voluntary preemption with efi_mm installed [ Upstream

[CVE-2026-90212][MODERATE REGULAR] arm64/efi: Avoid voluntary preemption with efi_mm installed [ Upstream

[AL-KERNEL]

CVE: CVE-2026-90212
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: arm64/efi: Avoid voluntary preemption with efi_mm installed [ Upstream
Commit: 829539c4a650544cb8e5e8690f2c2d0aa2c0e298
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=829539c4a650544cb8e5e8690f2c2d0aa2c0e298
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-90212
Analysis date: Fri, 18 Sep 2026 04:12:43 -0400
ActionableScore: 1
ActionableScore lower bound: unknown
Actionable bucket: Ordinary Moderate
Manual review required: NO

Summary:
No one-sentence report phrase was found.

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

The original Linux kernel CVE announcement for CVE-2026-90212 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-90212

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: NO

A detailed explanation of the methodology and priority rules is included
at the end of this message.

======================================================================
AL-KERNEL CLASSIFICATION RESULT
======================================================================

CVE-2026-90212	MODERATE	https://www.kernelcve.org/list/?q=CVE-2026-90212 CHECK WITH IMPACT FROM ORIG NN LOW	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:L/A:H';CWE-362;CWE-667;CWE-823;Other CVSS 'AV:L/AC:H/PR:H/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '5.8';DESCR 'An arm64 EFI runtime call can continue with an incorrect TTBR0_EL1 value because FPSIMD context handling may voluntarily preempt after the EFI address space has been installed. With software PAN enabled, deferred mm switching can restore a different address space before execution returns to EFI code. The confirmed result is an invalid kernel memory access followed by an Oops or kernel panic. Triggering requires an arm64 system with CONFIG_ARM64_SW_TTBR0_PAN, EFI runtime services, and a scheduling event during the vulnerable window, so the attack complexity is high. For the CVSS the PR:L value in the paranoid score represents a local user or restricted service with delegated access to an interface that invokes EFI runtime services. Administrative access is more typical and is represented by PR:H in the base score. The issue is not network reachable. Impact is at least local denial of service. Limited confidentiality or integrity impact remains a conservative possibility because EFI code can execute with an incorrect address translation context, but the available code does not demonstrate an arbitrary read or arbitrary write primitive.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate (with actual score 1)  SKIP CVE-2026-90212 UNKNOWN SKIP The Fixes patch not applied yet, so unlikely that actual: url YES  NO NO unknown 	MAYBE	OOB HARDWARE LINUS  DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN4	-	-	checked

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

ActionableScore=1
PrimitiveClass=CLASS_C
RealUAF=NO
HostAdminRequired=UNKNOWN
NamespaceScopedPrivilege=NO
ImportantCandidate=NO
ManualReview=RECOMMENDED
AutoDowngradeAllowed=YES

1. ActionableScore

* Raw conservative score: 1
* Conservative score: 1
* Raw paranoid score: 1
* Paranoid score: 1
* No floor or cap applied.
* Final recommended bucket: **Ordinary Moderate**::

2. Signal breakdown

* +1 Reliable kernel crash / strong DoS. The incorrect TTBR0_EL1 produces a demonstrated translation fault and kernel Oops. No additional Availability point is awarded for the same crash.
* +1 Weak or indirect corruption candidate. EFI execution resumes with an incorrect active address-translation context, but no useful read, write, disclosure, or replacement primitive is demonstrated.
* -1 Legacy or non-default execution mode. The defect specifically requires software PAN through CONFIG_ARM64_SW_TTBR0_PAN rather than the normal hardware PAN path.
* No race penalty. A scheduling event in the vulnerable interval is required, but the evidence does not establish that it is sufficiently narrow, rare, or difficult to repeat for a separate negative point.
* No rare-hardware penalty. Arm64 EFI hardware is not inherently rare, and the relevant restriction is already represented by the software PAN execution-mode penalty.
* No UAF, controlled reclaim, arbitrary write, repeated refcount mutation, information disclosure, or authorization bypass is established.
* No C or I point is awarded. Executing with the wrong TTBR0_EL1 is security-sensitive, but the supplied evidence only demonstrates an invalid access that faults.
* Active semantic-domain transition is not separately awarded. The address-space mismatch is already represented by the weak indirect corruption point, and there is no distinct bypass of a mapping-retirement protocol.
* Remote reachability and local unprivileged reachability are not established.

3. Reachability analysis

The affected system must be arm64, use EFI runtime services, and be built with CONFIG_ARM64_SW_TTBR0_PAN. A voluntary scheduling event must occur while `__efi_fpsimd_begin()` runs after the EFI-compatible TTBR0_EL1 has been installed.

The supplied material does not identify the userspace interface that initiated the failing EFI runtime request or establish whether an ordinary user, a delegated service, or only an administrator can invoke the complete path. Therefore, `HostAdminRequired` remains `UNKNOWN`, and no privilege bonus or penalty is applied.

EFI runtime state is global and is not an attacker-created namespace resource, so the complete operation is not namespace-scoped. There is no direct network trigger. The boot configuration and EFI support are prerequisites, but no unusual physical device is required.

4. Primitive and severity interpretation

The exact primitive is temporary execution of an EFI runtime path with an incorrect TTBR0_EL1 caused by voluntary preemption and deferred software-PAN address-space switching. This is an invalid active translation state, not a heap lifetime violation or stale object use.

There is no real UAF, repeated release, controlled replacement, arbitrary read, arbitrary write, or demonstrated access to protected data. The patch-supported consequence is a translation fault followed by an Oops and possible system-level DoS.

Limited confidentiality or integrity impact from the wrong translation context is theoretically conceivable, but no path shows EFI code successfully reading from or writing to an attacker-useful incorrect mapping before the fault. That possibility is therefore not scored, including in the paranoid result.

This is `CLASS_C`, not an Important candidate. Automatic downgrade is allowed because the established behavior is crash-oriented and no independently useful corruption or security-boundary primitive remains unresolved. Manual review is still recommended to confirm the permissions of the initiating EFI interface and whether architecture-specific firmware behavior permits any operation before the fault.

5. One-sentence report phrase

Voluntary preemption after installing the EFI address space can restore an incorrect TTBR0_EL1 on arm64 software PAN systems, causing a kernel translation fault and local denial of service without a demonstrated confidentiality, integrity, or privilege-escalation primitive.

6. Manual review recommendation

MANUAL CHECK RECOMMENDED

Confirm the initiating EFI runtime interface and whether affected firmware can perform any memory operation under the incorrect translation context before the demonstrated fault.

7. Call-site confidence

Call-site confidence: medium

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

Patch: arm64/efi: Avoid voluntary preemption with efi_mm installed [ Upstream
Commit: 829539c4a650544cb8e5e8690f2c2d0aa2c0e298
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=829539c4a650544cb8e5e8690f2c2d0aa2c0e298

Changed files:
  arch/arm64/kernel/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=829539c4a650544cb8e5e8690f2c2d0aa2c0e298

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

The original Linux kernel CVE announcement for CVE-2026-90212 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-90212

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:L/I:L/A:H
  The Best / paranoid CVSS score: 5.8

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: 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).