[CVE-2026-98923][LOW] arm64: io: Reject non-user protection in ioremap_prot() [ Upstream

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

CVE: CVE-2026-98923
Priority: LOW
AL-KERNEL base severity: LOW
KPANIC flag: NO
Patch: arm64: io: Reject non-user protection in ioremap_prot() [ Upstream
Commit: fddc90d4af4550af410f52d11bbf6b5f36443838
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=fddc90d4af4550af410f52d11bbf6b5f36443838
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98923
Analysis date: Tue, 27 Oct 2026 02:33:52 -0400
ActionableScore: 0
ActionableScore lower bound: unknown
Actionable bucket: Ordinary Moderate
Manual review required: NO

Summary:
A host-privileged arm64 `/dev/mem` mapping can provoke a spurious warning and optional `panic_on_warn` denial of service, without changing access authorization or corrupting memory.

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

The original Linux kernel CVE announcement for CVE-2026-98923 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98923

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.

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

CVE-2026-98923	LOW	https://www.kernelcve.org/list/?q=CVE-2026-98923 CHECK WITH IMPACT FROM ORIG NN LOW | AEGIS IMPACT LOW AEGIS_AS=0 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:N/A:H';*CWE-20;CWE-754;Other CVSS 'AV:L/AC:L/PR:H/UI:N/S:U/C:N/I:N/A:N';BEST CVSS score: '4.4';DESCR 'A valid PROT_NONE or execute only mapping created through devmem can reach ioremap_prot through generic_access_phys when proc cmdline is read. The missing PTE_USER bit causes a spurious WARN_ON_ONCE even though rejecting the read is expected behavior. For the CVSS the PR:H value is used because reliable triggering normally requires permission to map physical memory through devmem such as root or CAP_SYS_RAWIO. There is no demonstrated memory corruption or information disclosure primitive. Normal kernels continue after the warning, while systems configured with panic_on_warn may suffer a kernel panic and local denial of service. Automated impact decision path. The original SimpleNet classifier selected LOW. The primary LLM estimated paranoid CVSS 4.4 and the production ActionableScore returned 0 with recommendation Ordinary Moderate. The production rules then evaluated CVSS thresholds and ActionableScore thresholds. No severity changing production threshold or specialist override was recorded. 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. The independent weaker Aegis shadow evaluated CVSS 0.0 and ActionableScore 0 with primitive class NONE 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	WARNONLY HARDWARE LINUS 	-	-	checked

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

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

1. ActionableScore

* Raw base score: -1 (+1 plausible panic under `panic_on_warn`; -2 host-level `/dev/mem` access privilege).
* Conservative score: 0 after clamping the negative result.
* Raw paranoid score: -1.
* Paranoid score: 0 after clamping; no separate technically supported impact.
* Final recommended bucket: **Ordinary Moderate**::

2. Signal breakdown

* +1 Reliable kernel crash / strong DoS: the reachable `WARN_ON_ONCE()` can panic systems configured with `panic_on_warn`.
* -2 Full host-admin-equivalent privilege: constructing the demonstrated physical-memory mapping requires host-level `/dev/mem` access, ordinarily gated by host `CAP_SYS_RAWIO` and device permissions.
* No corruption points: the old code warns and immediately returns `NULL`; the patch preserves rejection while removing the warning.
* No authorization-bypass points: there is no DENY-to-ALLOW transition. Both versions reject protection lacking `PTE_USER`.
* No confidentiality or integrity points: no bytes are disclosed or modified.
* No extra availability point: it would duplicate the same warning-induced panic.
* NEW52/B5-R and NEW53/B3-PENDING do not apply: there is no OOB write or shared-backing write.

3. Reachability analysis

The demonstrated trigger requires creating a `/dev/mem` physical mapping with `PROT_NONE` or execute-only protection, followed by procfs command-line access. Physical-memory mapping is not an attacker-obtainable namespace capability and requires host-level raw-I/O authority; numeric UID 0 is not strictly required because the capability can suffice. No race, special hardware, or retry sequence is involved.

4. Primitive and severity reading

The defect is a spurious warning on a valid but unreadable user mapping. It is neither memory corruption nor an authorization flaw: `ioremap_prot()` already returns `NULL`, and the fix only replaces `WARN_ON_ONCE(condition)` with the same condition as a quiet rejection. The supported effect is at most host DoS under `panic_on_warn`; normal kernels continue. Therefore the primitive class is NONE, Important review is unwarranted, and automatic downgrade is safe.

5. One-sentence report phrase

A host-privileged arm64 `/dev/mem` mapping can provoke a spurious warning and optional `panic_on_warn` denial of service, without changing access authorization or corrupting memory.

6. Manual review advice

NO MANUAL CHECK NEEDED

The patch proves quiet validation of an already-rejected mapping, with no unresolved corruption or authorization boundary.

7. Call-site confidence

Call-site confidence: high

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

Patch: arm64: io: Reject non-user protection in ioremap_prot() [ Upstream
Commit: fddc90d4af4550af410f52d11bbf6b5f36443838
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=fddc90d4af4550af410f52d11bbf6b5f36443838

Changed files:
  arch/arm64/include/asm/io.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=fddc90d4af4550af410f52d11bbf6b5f36443838

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

The original Linux kernel CVE announcement for CVE-2026-98923 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98923

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:N
  The Best / paranoid CVSS vector: AV:L/AC:L/PR:H/UI:N/S:U/C:N/I:N/A:H
  The Best / paranoid CVSS score: 4.4

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).