[CVE-2026-81015][MODERATE 7.0] platform/x86/amd/pmc: Fix LPS0 and debugfs leaks when STB init fails

[CVE-2026-81015][MODERATE 7.0] platform/x86/amd/pmc: Fix LPS0 and debugfs leaks when STB init fails

[AL-KERNEL]

CVE: CVE-2026-81015
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: platform/x86/amd/pmc: Fix LPS0 and debugfs leaks when STB init fails
Commit: bc9aa5fe21c3966c80647ed6574b94b863f23c62
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=bc9aa5fe21c3966c80647ed6574b94b863f23c62
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-81015
Analysis date: Sat, 12 Sep 2026 05:58:05 -0400
ActionableScore: 5
ActionableScore lower bound: 4
Actionable bucket: Actionable Moderate
Manual review required: NO

Summary:
No one-sentence report phrase was found.

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

The original Linux kernel CVE announcement for CVE-2026-81015 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-81015

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 7.0
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-2026-81015	MODERATE	https://www.kernelcve.org/list/?q=CVE-2026-81015 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-772;CWE-459;*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 'amd_pmc_probe can leave the LPS0 s2idle handler and debugfs directory registered when amd_stb_s2d_init fails late in probe. The stale LPS0 registration remains on a global ACPI list while devm managed driver state may be torn down, so a later module reload can hit list corruption and a later s2idle transition can call into invalid driver state. For the CVSS the PR:L is used for the paranoid score because a local user or service may be able to trigger suspend or related power management paths after the failed probe state exists, although reliable creation of that failed probe state is usually administrative. The issue is not network reachable. Impact is at least a local denial of service via kernel BUG or crash and in worst case may allow limited confidentiality or integrity impact due to stale pointer use and should be reviewed manually.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate (with actual score 5)	YES	INIT LEAK ERRORPATH DEBUGFS  KPANIC INCREASED_FROM_LOW_BASED_ON_REQUIREMANUALCHECK	YES	NO	checked

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

ActionableScore=5
ActionableScoreLower=4
PrimitiveClass=CLASS_B
RealUAF=YES
HostAdminRequired=UNKNOWN
NamespaceScopedPrivilege=NO
ImportantCandidate=NO
ManualReview=RECOMMENDED
AutoDowngradeAllowed=NO

1. ActionableScore

* Raw conservative score: 4
* Conservative score: 4. No floor or cap changed the score.
* Raw paranoid score: 5
* Paranoid score: 5. No floor or cap changed the score.
* Final recommended bucket: **Actionable Moderate**::

2. Signal breakdown

Conservative signals:

* +2 Real UAF / lifetime violation. The LPS0 s2idle handler remains registered after probe failure while devm managed driver state backing the handler may be torn down. A later s2idle transition can call into invalid driver state.
* +1 Reliable kernel crash / strong DoS. The supplied trace shows list_add corruption and kernel BUG during module reload. The commit also states that s2idle can call into torn down state.
* +1 Concrete persistent kernel resource/reference leak. The failed probe path leaves the LPS0 registration and debugfs directory behind instead of unwinding them.

Conservative negatives:

* 0 Host admin penalty not applied. Host admin is plausible for module reload or forced repro, but it is not positively established for all consequences because s2idle may be triggered after the failed probe state exists.
* 0 Race/timing penalty not applied. This is an ordered failed-probe cleanup bug, not a demonstrated narrow race.
* 0 Hardware rarity penalty not applied. AMD PMC is platform specific, but no rare physical hardware prerequisite is established beyond affected AMD platforms.

Paranoid additional signal:

* +1 Active stale registration beyond ordinary cleanup fault. The stale LPS0 registration is not only a leaked debugfs entry or passive metadata. It remains on a global ACPI path and can dispatch into torn down driver state during later power-management activity. This supports Actionable Moderate review, but not Class A.

Material non-awarded signals:

* Controlled reclaim not demonstrated.
* Arbitrary read/write not demonstrated.
* Concrete repeated release/refcount mutation not established.
* Structured stale-object leverage in the strong sense not awarded because attacker-controlled replacement or attacker-shaped post-free contents are not shown.
* Weak LPE not separately awarded beyond the paranoid active-stale-registration concern.
* Extra Availability not awarded because the same crash/BUG is already counted once.
* Confidentiality and integrity bonuses not awarded because no disclosure, protected-object modification, or privilege-escalation chain is established.
* Network reachability not established.

3. Reachability analysis

The bug is reached when amd_pmc_probe registers LPS0 s2idle operations and debugfs, then amd_stb_s2d_init fails late in probe. The demonstrated crash path involves reloading the module after this failed state, which normally suggests host-administrative control. However, the commit also states that even without reload the next s2idle transition can call into torn-down driver state. On many systems suspend or s2idle may be initiated by a local user session or by a power-management service, but the input does not prove that an ordinary user can create the failed probe state.

Therefore HostAdminRequired is UNKNOWN rather than YES or NO. NamespaceScopedPrivilege is NO because this platform driver and ACPI LPS0 path are not namespace-scoped. There is no network trigger. Prior host setup may exist in practice because the affected driver must be present and the failed probe condition must occur, but the scoring does not subtract for that uncertainty. No special rare hardware penalty is applied beyond affected AMD PMC-capable systems.

4. Primitive and severity interpretation

The exact primitive is stale global registration of an LPS0 s2idle handler plus a debugfs leak after a late probe failure. The stale registration can survive after devm-managed state is destroyed, making later ACPI power-management callbacks use invalid driver state. This is an active structured lifetime violation rather than a simple passive memory leak.

This is not a concrete repeated-release/refcount case. There is no visible first put followed by a second put on the exact same potentially freed reference. The demonstrated consequence is kernel BUG/list corruption on reload and possible crash on later s2idle. The speculative consequence is broader post-lifetime misuse of driver state, but controlled reclaim, callback hijack from reclaimed data, arbitrary write, and LPE are not established.

PrimitiveClass is CLASS_B because a real stale post-lifetime object use is directly implied. ImportantCandidate is NO because the evidence currently supports Actionable Moderate review rather than a strong Important candidate. AutoDowngradeAllowed is NO because automatic closure would lose a concrete stale active registration that can call into torn-down kernel state, even though proven exploitation beyond DoS is absent.

5. One-sentence report phrase

A failed amd_pmc probe can leave the LPS0 s2idle handler registered after its backing driver state is torn down, allowing later module reload or s2idle activity to hit list corruption or call into invalid state and crash the kernel.

6. Manual review recommendation

MANUAL CHECK RECOMMENDED

Reason: this is more than a pure debugfs leak because a global LPS0 callback registration can survive past driver-state teardown, but current evidence does not show controlled reclaim, arbitrary R/W, or demonstrated privilege escalation.

7. Call-site confidence

Call-site confidence: medium

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

Patch: platform/x86/amd/pmc: Fix LPS0 and debugfs leaks when STB init fails
Commit: bc9aa5fe21c3966c80647ed6574b94b863f23c62
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=bc9aa5fe21c3966c80647ed6574b94b863f23c62

Commit description:

amd_pmc_probe() registers the LPS0 s2idle handler with
acpi_register_lps0_dev() and creates the driver's debugfs directory before
calling amd_stb_s2d_init(), which is the last step in probe that can fail.

When amd_stb_s2d_init() fails (for example the S2D telemetry region cannot
be ioremapped on a long-running system, or the SMU rejects the S2D setup)
the error path only calls pci_dev_put() and returns.  This leaves
amd_pmc_s2idle_dev_ops on the global lps0_s2idle_devops_head list and leaks
the debugfs directory, while the devm-managed resources backing the handler
are torn down.

Reloading the module then walks the corrupted list in
acpi_register_lps0_dev() and hits:

  list_add corruption. next->prev should be prev, but was NULL.
  kernel BUG at lib/list_debug.c:29!
   acpi_register_lps0_dev+0x44/0x80
   amd_pmc_probe+0x224/0x380 [amd_pmc]
   platform_probe+0x67/0x90

Even without a reload, the stale registration means the next s2idle
transition calls into torn-down driver state.

Unwind the debugfs directory and the LPS0 registration on the
amd_stb_s2d_init() error path.  acpi_unregister_lps0_dev() is safe to call
unconditionally here: it is guarded on the same conditions as
acpi_register_lps0_dev(), which is exactly what amd_pmc_remove() already
relies on.

Reported-by: Francis De Brabandere <francisdb@gmail.com>
Closes: https://bugzilla.kernel.org/show_bug.cgi?id=221759
Tested-by: Francis De Brabandere <francisdb@gmail.com>
Fixes: 83ad697 ("platform/x86/amd/pmc: Move STB block into amd_pmc_s2d_init()")
Cc: stable@vger.kernel.org
Signed-off-by: Mario Limonciello <mario.limonciello@amd.com>
Link: https://patch.msgid.link/20260721181756.143084-6-mario.limonciello@amd.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:
  lib/list_debug.c
  drivers/platform/x86/amd/pmc/pmc.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=bc9aa5fe21c3966c80647ed6574b94b863f23c62

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

The original Linux kernel CVE announcement for CVE-2026-81015 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-81015

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: 4
  Paranoid ActionableScore: 5

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: YES
Published priority for this report (same as in Subject): MODERATE 7.0

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).