[CVE-2026-89443][MODERATE REGULAR] platform/x86: ISST: Validate level in perf mask ioctls

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

CVE: CVE-2026-89443
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: platform/x86: ISST: Validate level in perf mask ioctls
Commit: 1a8bab5ceee1a42a78de12d3d69f67516a20588e
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=1a8bab5ceee1a42a78de12d3d69f67516a20588e
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89443
Analysis date: Fri, 11 Sep 2026 20:09:12 -0400
ActionableScore: 2
ActionableScore lower bound: 1
Actionable bucket: Ordinary Moderate
Manual review required: NO

Summary:
No one-sentence report phrase was found.

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

The original Linux kernel CVE announcement for CVE-2026-89443 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89443

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.

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

CVE-2026-89443	MODERATE	https://www.kernelcve.org/list/?q=CVE-2026-89443 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:N/A:L';CWE-125;CWE-129;*CWE-20;Other CVSS 'AV:L/AC:L/PR:L/UI:N/S:U/C:L/I:N/A:N';BEST CVSS score: '4.4';DESCR 'The Intel ISST ioctl path used a user supplied level value as an index for per level performance data without validating it against max_level first. A local process with access to the ISST device interface could pass an invalid level to the perf mask or base frequency mask ioctl and trigger an out of bounds read from the per level offset data. For the CVSS the PR:L value is used because triggering requires local code execution and access to the ioctl interface, but does not require a remote network position. The issue is not network reachable. Impact is mainly limited confidentiality exposure from an OOB read candidate, with low availability impact only in the paranoid score if invalid offsets cause driver errors or faults. No direct privilege escalation or memory corruption write primitive is indicated by the patch context.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate (with actual score 2)	YES	READ OOB SIMPLEFIX IMPROVEONLY  DECREASED_TO_MODERATE_REGULAR_FROM_MODERATE7_BASED_ON_GUESSCVSS	YES	NO	checked

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

ActionableScore=2
ActionableScoreLower=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. No floor or cap changed the score.
* Raw paranoid score: 2
* Paranoid score: 2. No floor or cap changed the score.
* Final recommended bucket: **Ordinary Moderate**::

2. Signal breakdown

Conservative positive signals:

* +1 Weak / indirect corruption candidate. The ioctl level value is user supplied and used as an index into per level ISST data without checking max_level first. This establishes an unchecked index / read only OOB candidate.

Paranoid positive signals:

* +1 Weak / indirect corruption candidate. Same as conservative.
* +1 Limited confidentiality concern. The affected helpers are mask ioctls, so the invalid per level lookup may influence data returned to userspace. This is only a limited disclosure concern, not an arbitrary kernel read.

Non-awarded signals:

* Real UAF not awarded. No lifetime violation, stale object, refcount misuse, or double release is shown.
* Strong corruption not awarded. No OOB write, arbitrary write, controlled reclaim, type confusion, or callback influence is shown.
* Reliable kernel crash not awarded. The patch mentions OOB reads, not a demonstrated panic or host-wide fault.
* Remote reachability not awarded. The bug is reached through a local platform driver ioctl, not network traffic.
* Local unprivileged trigger not awarded. Access to the ISST ioctl interface is required, but the supplied evidence does not prove ordinary unprivileged reachability.
* Host-admin penalty not awarded. Host-admin-equivalent privilege is not positively established.
* C/I escalation beyond limited read not awarded. The patch does not show a write primitive, security-boundary bypass, or privilege escalation path.
* Manual Important preservation not applied. This is a validation / bounds-checking bug with limited OOB read evidence only.

3. Reachability analysis

The vulnerable path is a local ioctl path in the Intel ISST platform driver. A local process must be able to open and use the relevant ISST device interface and provide an invalid level value to isst_if_get_perf_level_mask() or isst_if_get_base_freq_mask().

The supplied evidence does not prove that host root or host-admin-equivalent capability is required for the complete trigger, so HostAdminRequired is UNKNOWN rather than YES. It also does not prove that an ordinary unprivileged user can reach the ioctl interface, so HostAdminRequired is not NO and no local-unprivileged bonus is applied.

This is not namespace scoped. The vulnerable object is platform / hardware management state, not a per-user-namespace or per-network-namespace object. No prior network setup or packet path is involved. Special Intel SST / ISST capable hardware or platform support is relevant for exposure, but no rare-hardware penalty is applied because the evidence only shows a hardware-specific driver path, not a physical-only attacker model. No race is involved.

4. Primitive and severity interpretation

The exact primitive is a user-controlled level value used as an unchecked index into per-level performance / base-frequency data, leading to a read-only out-of-bounds access from the per-level offset table or adjacent per-level data.

This is not active structured UAF and not fixed stale storage. There is no cleanup/destructor lifetime issue and no repeated release/refcount operation. The demonstrated primitive is an invalid indexed read caused by missing bounds validation.

PrimitiveClass is CLASS_C because the established behavior is a limited OOB read / invalid-state ioctl handling issue without an independently useful corruption primitive. The demonstrated consequence is low-grade information exposure or incorrect hardware data access. A fault is possible only as a paranoid availability concern, but not sufficiently demonstrated for an ActionableScore DoS point.

ImportantCandidate is NO because there is no UAF, no write primitive, no security-boundary bypass, no protected file/page ownership violation, and no demonstrated LPE chain. AutoDowngradeAllowed is YES because this is a constrained validation bug with no unresolved Important-grade primitive.

Likely operational severity is Low to ordinary Moderate. It is still worth checking device permissions and returned data behavior, but it should not be treated as an Important-class kernel vulnerability from the supplied patch alone.

5. One-sentence report phrase

Intel ISST perf mask ioctls used a user supplied level without max_level validation, allowing a local caller with ISST ioctl access to trigger a limited out of bounds read from per level data.

6. Manual review recommendation

MANUAL CHECK RECOMMENDED

Reason: the issue is an OOB read candidate in a local ioctl path, and manual verification should confirm device-node permissions and whether invalid indexes can return sensitive data or only invalid hardware masks.

7. Call-site confidence

Call-site confidence: medium

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

Patch: platform/x86: ISST: Validate level in perf mask ioctls
Commit: 1a8bab5ceee1a42a78de12d3d69f67516a20588e
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=1a8bab5ceee1a42a78de12d3d69f67516a20588e

Commit description:

isst_if_get_perf_level_mask() and isst_if_get_base_freq_mask() use the
user-provided level as an index into perf_levels[] via
_read_pp_level_info() and _read_bf_level_info(), but neither helper
validates it first.

The adjacent level-info helpers reject levels above max_level before
reading the same per-level register block. Add the same bounds checks to
the mask helpers, and reject disabled SST-PP levels in
isst_if_get_perf_level_mask() to match isst_if_get_perf_level_info().

This prevents out-of-bounds reads from the per-level offset table on
invalid ioctl input.

Fixes: ea009e4 ("platform/x86: ISST: Add SST-PP support via TPMI")
Fixes: 06a61df ("platform/x86: ISST: Add SST-BF support via TPMI")
Cc: stable@vger.kernel.org
Assisted-by: Claude:claude-opus-5
Signed-off-by: HyeongJun An <sammiee5311@gmail.com>
Acked-by: Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>
Link: https://patch.msgid.link/20260807144003.3498972-3-sammiee5311@gmail.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=1a8bab5ceee1a42a78de12d3d69f67516a20588e

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

The original Linux kernel CVE announcement for CVE-2026-89443 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89443

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:L/UI:N/S:U/C:L/I:N/A:N
  The Best / paranoid CVSS vector: AV:L/AC:L/PR:L/UI:N/S:U/C:L/I:N/A:L
  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: 1
  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: 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).