[CVE-2026-89438][MODERATE REGULAR] platform/x86: ISST: Validate logical CPU id and clos id

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

CVE: CVE-2026-89438
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: platform/x86: ISST: Validate logical CPU id and clos id
Commit: c9ee2770eb95ba316a56d776b2b66666b70c194b
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=c9ee2770eb95ba316a56d776b2b66666b70c194b
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89438
Analysis date: Sat, 12 Sep 2026 00:36:51 -0400
ActionableScore: 3
ActionableScore lower bound: 2
Actionable bucket: Borderline / manual review recommended
Manual review required: YES

Summary:
No one-sentence report phrase was found.

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

The original Linux kernel CVE announcement for CVE-2026-89438 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89438

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: 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
======================================================================

CVE-2026-89438	MODERATE	https://www.kernelcve.org/list/?q=CVE-2026-89438 CHECK WITH IMPACT FROM ORIG NN MODERATE	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:L/PR:L/UI:N/S:U/C:L/I:L/A:H';*CWE-20;CWE-129;CWE-823;Other CVSS 'AV:L/AC:L/PR:H/UI:N/S:U/C:N/I:L/A:L';BEST CVSS score: '6.6';DESCR 'Intel ISST TPMI did not validate the CLOS ID and logical CPU ID before using them to calculate an MMIO offset for core power configuration. A local actor with access to the ISST control interface could provide out of range values and make the driver access an unintended MMIO location. For the CVSS the PR:L is used in the paranoid score because this interface may be delegated to a reduced capability root user, a service account, or a platform management component rather than only full host root. The issue is not network reachable and requires local access to the management path. Impact is at least incorrect hardware configuration or local denial of service, and in the worst still defensible case may include limited confidentiality or integrity impact from unintended MMIO read/write behavior.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Borderline / manual review recommended (with actual score 3)	YES	DANGER SIMPLEFIX LOG HARDWARE  DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN4	YES	NO	checked

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

ActionableScore=3
ActionableScoreLower=2
PrimitiveClass=CLASS_C
RealUAF=NO
HostAdminRequired=UNKNOWN
NamespaceScopedPrivilege=NO
ImportantCandidate=NO
ManualReview=RECOMMENDED
AutoDowngradeAllowed=YES

1. ActionableScore

* Raw conservative score: 2
* Conservative score: 2. No floor or cap changed the score.
* Raw paranoid score: 3
* Paranoid score: 3. No floor or cap changed the score.
* Final recommended bucket: **Borderline / manual review recommended**::

2. Signal breakdown

Conservative positive signals:

* +1 Weak / indirect corruption candidate. User supplied CLOS ID and logical CPU ID are used to calculate an MMIO offset without bounds validation.
* +1 Integrity plausible. An out of range MMIO offset may access unintended platform power management registers or apply an unintended CLOS association.

Paranoid additional signal:

* +1 Availability impact plausible. Incorrect MMIO access in a CPU power management path may destabilize platform behavior or cause local DoS, although a concrete kernel crash is not demonstrated.

Negative or non-awarded signals:

* +0 Real UAF not awarded. No stale object, release-after-free, refcount misuse, or lifetime violation is shown.
* +0 Strong corruption primitive not awarded. The patch does not establish arbitrary kernel write, controlled reclaim, heap overwrite, or callback control.
* +0 Confidentiality not awarded. A read-back or disclosure path from unintended MMIO access is not shown.
* +0 Reliable kernel crash not awarded. The commit does not show panic, Oops, WARN-to-crash, or confirmed host-wide fatal failure.
* +0 Local unprivileged trigger not awarded. The provided context does not establish that ordinary unprivileged users can access the complete ISST TPMI control interface.
* +0 Remote reachability not awarded. The vulnerable operation is a local platform management path, not packet processing or network service input.
* +0 Hardware rarity penalty not applied. The code is hardware-specific, but the prompt requires concrete evidence that the hardware is rare or physical-only before subtracting points.
* +0 Host-admin penalty not applied. Host-admin-equivalent privilege is not positively established by the supplied patch context.

3. Reachability analysis

The trigger is local input to the Intel ISST TPMI control interface. The patch shows copy_from_user() values reaching CLOS and logical CPU handling, but it does not show the device node permissions, ioctl gate, capability checks, or product policy around access to that interface.

HostAdminRequired is therefore UNKNOWN. It may be root or a privileged platform management daemon in many deployments, but the supplied evidence does not positively prove host-admin-equivalent privilege for the complete path. NamespaceScopedPrivilege is NO because this is a platform x86 hardware management interface, not a network namespace scoped operation.

There is no network trigger. Prior platform support for Intel ISST TPMI and the affected driver path is required. No race is involved. The issue is deterministic input validation failure rather than timing dependent behavior.

4. Primitive and severity interpretation

The exact primitive is unchecked user controlled index values used in MMIO offset calculation. This is not a kernel heap UAF, not an OOB write into normal kernel memory, and not a repeated release/refcount bug.

The best classification is CLASS_C: invalid state / unsafe MMIO selection with plausible device or platform state impact, but without an independently demonstrated useful kernel corruption primitive. The demonstrated consequence is incorrect or unintended hardware register access. The speculative consequence is local DoS or limited platform configuration integrity impact if the computed MMIO offset reaches sensitive registers.

ImportantCandidate is NO because no Class A primitive, real UAF, controlled corruption, authorization bypass, or demonstrated LPE path is established. ManualReview is RECOMMENDED because MMIO offset bugs can be platform-specific and the affected register layout determines whether impact is harmless, device-local, or system-relevant. AutoDowngradeAllowed is YES because the evidence supports a borderline validation flaw rather than unresolved Important-grade memory corruption or security-boundary bypass.

5. One-sentence report phrase

Unchecked CLOS ID and logical CPU ID values in the Intel ISST TPMI path could be used to calculate out of range MMIO offsets, potentially causing unintended platform power register access and limited local integrity or availability impact.

6. Manual review recommendation

MANUAL CHECK RECOMMENDED

Reason: the patch shows an unsafe MMIO offset calculation from user controlled fields, but the supplied context does not establish kernel memory corruption, UAF, LPE, remote reachability, or a confirmed crash.

7. Call-site confidence

Call-site confidence: medium

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

Patch: platform/x86: ISST: Validate logical CPU id and clos id
Commit: c9ee2770eb95ba316a56d776b2b66666b70c194b
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=c9ee2770eb95ba316a56d776b2b66666b70c194b

Commit description:

Validate max CLOS ID and logical CPU ID for core power feature.
Reject any clos level or logical CPU number greater than the
supported maximum. These are used to calculate MMIO offset.

Fixes: 12a7d2c ("platform/x86: ISST: Add SST-CP support via TPMI")
Cc: stable@vger.kernel.org
Signed-off-by: Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>
Link: https://patch.msgid.link/20260811221514.3905817-2-srinivas.pandruvada@linux.intel.com
Reviewed-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  drivers/platform/x86/intel/speed_select_if/isst_tpmi_core.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=c9ee2770eb95ba316a56d776b2b66666b70c194b

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

The original Linux kernel CVE announcement for CVE-2026-89438 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89438

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:L/A:L
  The Best / paranoid CVSS vector: AV:L/AC:L/PR:L/UI:N/S:U/C:L/I:L/A:H
  The Best / paranoid CVSS score: 6.6

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: 2
  Paranoid ActionableScore: 3

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).