[CVE-2026-89589][MODERATE REGULAR] acpi/apei/ghes: Use raw_spinlock_t for CXL CPER work locks

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

CVE: CVE-2026-89589
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: acpi/apei/ghes: Use raw_spinlock_t for CXL CPER work locks
Commit: c735dbce7ad03df708bf22ec964f67e43cbc823a
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=c735dbce7ad03df708bf22ec964f67e43cbc823a
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89589
Analysis date: Sat, 12 Sep 2026 03:19:28 -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-2026-89589 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89589

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-2026-89589	MODERATE	https://www.kernelcve.org/list/?q=CVE-2026-89589 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-667;*CWE-833;CWE-362;*CWE-416;Other CVSS 'AV:L/AC:H/PR:H/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '5.8';DESCR 'CXL CPER work registration can deadlock with GHES hard IRQ posting because the registration path used a normal spinlock with local interrupts enabled while the IRQ path used irqsave locking on the same lock. If a GHES interrupt arrives on the same CPU while the lock is held, the IRQ handler can spin forever while the interrupted lock holder cannot run, causing a local denial of service. The unregister path also had a race window around the global work pointer and cancel_work_sync, where an interrupt could schedule work on a pointer that is about to be freed. For the CVSS the PR:L is used for the paranoid score because delegated local RAS tooling, device management, or reduced capability service control may be enough in some deployments, although the base case is closer to PR:H. The issue is not network reachable and normally depends on local platform access plus CXL/GHES error delivery. Impact is at least denial of service via deadlock. In the paranoid interpretation it may have limited confidentiality or integrity impact due to the stale work pointer race and should be reviewed manually.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Borderline / manual review recommended (with actual score 3)	YES	DEADLOCK WARNONLY HARDWARE  INCREASED_FROM_LOW_BASED_ON_REQUIREMANUALCHECK 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
* Raw paranoid score: 3
* Paranoid score: 3
* Final recommended bucket: **Borderline / manual review recommended**::

No floor or cap changed the score.

2. Signal breakdown

Conservative signals:

* +1 Reliable kernel DoS. The commit directly describes a same CPU hard IRQ deadlock where the IRQ handler spins on a lock held by the interrupted context.
* +1 Hard IRQ synchronization defect. The bug is in synchronization between process context register/unregister paths and GHES hard IRQ post paths, including PREEMPT_RT unsafe locking semantics.

Paranoid additional signal:

* +1 Weak lifetime concern. The unregister restructuring addresses a race where a CPER interrupt could schedule work on a global work pointer that is about to be freed. This is a lifetime hazard but not enough evidence for a confirmed post-free use.

Negative or non-awarded signals:

* RealUAF not awarded. The patch says pointer about to be freed, but the supplied context does not conclusively establish an actual use after free or a second lifetime/refcount mutation after free.
* Concrete repeated release/refcount not awarded. No first release followed by second put/free/refcount mutation on the exact same dangling reference is shown.
* Structured stale-object leverage not awarded. The possible stale work pointer issue is not shown to consume attacker-controlled replacement fields or callbacks after reuse.
* Strong LPE or controlled corruption not awarded. No controlled reclaim, arbitrary write, callback hijack, refcount takeover, or privilege escalation path is established.
* Extra Availability not awarded. The deadlock is already counted as the DoS consequence.
* Remote reachability not awarded. GHES/CXL error delivery is platform and firmware mediated, not direct network input.
* Host-admin penalty not applied as -2. Module or driver lifecycle control is likely privileged, but the complete attacker privilege boundary is not fully established by the supplied text.

3. Reachability analysis

The directly affected paths are CXL CPER work registration, unregistration, and GHES hard IRQ posting. The deadlock requires a CPU to be in a register or unregister path while a GHES interrupt arrives on the same CPU and tries to take the same lock.

A reliable attacker model is not fully established. Triggering register or unregister paths generally relates to module or driver lifecycle and likely requires privileged local control. Triggering the GHES interrupt side depends on CXL/GHES platform error delivery and may require hardware, firmware, RAS tooling, or device error injection. This is not namespace scoped. No evidence shows that an ordinary unprivileged user can complete the trigger chain.

Prior platform support for CXL/GHES is required. This is not direct network exposure. The timing condition is real because the deadlock needs an interrupt while the lock holder is preempted, but the score does not rely on a hard race penalty because the supplied evidence does not quantify rarity or attacker repeatability.

4. Primitive and severity interpretation

The established primitive is primarily an IRQ locking deadlock caused by taking the same lock with local interrupts enabled in one path and irqsave from hard IRQ context in another path. This is CLASS_C because the demonstrated behavior is deadlock and denial of service.

The patch also addresses a workqueue lifetime ordering issue by clearing the global work pointer under the lock before cancel_work_sync and resetting the kfifo after quiescing work. This creates a weak lifetime concern, but the supplied evidence does not prove an actual post-free work_struct use, controlled reuse, repeated lifetime mutation, or an exploitable stale structured object.

ImportantCandidate is NO because no Class A primitive and no sufficiently strong Class B unresolved corruption primitive is established. ManualReview is RECOMMENDED because the bug touches hard IRQ locking, PREEMPT_RT semantics, and a possible workqueue lifetime race. AutoDowngradeAllowed is YES because the established impact is local/platform DoS and no meaningful unresolved exploitation primitive beyond the deadlock/lifetime warning is proven.

Likely operational severity is borderline to ordinary Moderate, with manual review useful mainly to confirm whether any product-specific CXL/GHES error injection path is reachable below host admin.

5. One-sentence report phrase

CXL CPER work registration and unregistration can deadlock with GHES hard IRQ posting because the same work locks are taken with incompatible interrupt semantics, and the unregister path also had a possible stale work pointer scheduling window during teardown.

6. Manual review recommendation

MANUAL CHECK RECOMMENDED

Reason: the confirmed impact is DoS, but hard IRQ context plus workqueue teardown ordering should be checked against product-specific CXL/GHES exposure and any delegated RAS error injection capability.

7. Call-site confidence

Call-site confidence: high

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

Patch: acpi/apei/ghes: Use raw_spinlock_t for CXL CPER work locks
Commit: c735dbce7ad03df708bf22ec964f67e43cbc823a
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=c735dbce7ad03df708bf22ec964f67e43cbc823a

Commit description:

The CXL CPER work registration and unregistration helpers acquire
cxl_cper_work_lock and cxl_cper_prot_err_work_lock with a spinlock
guard(), which leaves local interrupts enabled. The corresponding post
paths (cxl_cper_post_event(), cxl_cper_post_prot_err()) execute in hard
IRQ context (they are called from the GHES error notification path) and
acquire the same locks with an irqsave guard().

If a CPU is holding one of these locks via a spinlock guard() when a GHES
interrupt arrives on the same CPU, the IRQ handler spins on the held lock
waiting for it to release, while the lock holder is preempted by the IRQ.
The result is a deadlock.

Convert both locks from spinlock_t to raw_spinlock_t and use guard() at
all call sites. On PREEMPT_RT kernels spinlock_t is backed by rt_mutex and
sleeping from hard IRQ context is not permitted; raw_spinlock_t is safe in
both contexts.

Add WARN_ONCE to both register functions to surface double-registration
bugs at runtime.

Restructure both unregister functions to clear the global work pointer
under the lock before calling cancel_work_sync(), closing the window
where a CPER interrupt could schedule work on a pointer about to be
freed. Add kfifo_reset() after cancel_work_sync() so stale entries
are not replayed on next module load.

Both kfifos are single-consumer: only one work_struct is registered at
a time, enforced by the WARN_ONCE guard in the register functions.
kfifo_reset() is safe outside the lock because cancel_work_sync() has
already quiesced the consumer, and no new consumer can register until
the current module exit completes and a fresh module init runs.

Remove the redundant cancel_work_sync() call from cxl_ras_exit() and
cxl_pci_driver_exit(). The CPER unregister functions now quiesce
the work internally.

Reported-by: Sashiko <sashiko@linuxfoundation.org>
Signed-off-by: Terry Bowman <terry.bowman@amd.com>
Fixes: 5e4a264 ("acpi/ghes: Process CXL Component Events")
Fixes: 36f257e ("acpi/ghes, cxl/pci: Process CXL CPER Protocol Errors")
Cc: stable@vger.kernel.org
Reviewed-by: Dave Jiang <dave.jiang@intel.com>
Reviewed-by: Jonathan Cameron <jonathan.cameron@oss.qualcomm.com>
Reviewed-by: Tony Luck <tony.luck@intel.com>
Link: https://patch.msgid.link/20260803221810.3685703-4-terry.bowman@amd.com
Signed-off-by: Dave Jiang <dave.jiang@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  drivers/acpi/apei/ghes.c
  drivers/cxl/core/ras.c
  drivers/cxl/pci.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=c735dbce7ad03df708bf22ec964f67e43cbc823a

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

The original Linux kernel CVE announcement for CVE-2026-89589 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89589

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: 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).