[CVE-2026-98473][LOW] s390/vfio-ap: fix KVM GISC and page leak when queue removed from host config

[CVE-2026-98473][LOW] s390/vfio-ap: fix KVM GISC and page leak when queue removed from host config

[AL-KERNEL]

CVE: CVE-2026-98473
Priority: LOW
AL-KERNEL base severity: LOW
KPANIC flag: NO
Patch: s390/vfio-ap: fix KVM GISC and page leak when queue removed from host config
Commit: da69d3ac53490724eba0ade9deb4e539a6ae9034
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=da69d3ac53490724eba0ade9deb4e539a6ae9034
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98473
Analysis date: Sat, 24 Oct 2026 10:00:23 -0400
ActionableScore: 2
ActionableScore lower bound: unknown
Actionable bucket: Ordinary Moderate
Manual review required: NO

Summary:
VFIO-AP queue removal can leak a pinned guest page and GISC registration and retain a stale ISC identifier, but no concrete UAF, OOB write, or attacker-controlled duplicate release is shown.

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

The original Linux kernel CVE announcement for CVE-2026-98473 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98473

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-2026-98473	LOW	https://www.kernelcve.org/list/?q=CVE-2026-98473 CHECK WITH IMPACT FROM ORIG NN MODERATE | AEGIS IMPACT MODERATE AEGIS_AS=1 LEGACY=LOW RESULT=DIFF (final Legacy and Aegis differ; FINAL: LOW, Aegis: MODERATE)	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H';*CWE-772;*CWE-401;CWE-415;Other CVSS 'AV:L/AC:H/PR:L/UI:R/S:U/C:N/I:N/A:L';BEST CVSS score: '4.7';DESCR 'The s390 vfio ap cleanup paths can retain a KVM GISC registration and a pinned guest page when an assigned AP queue becomes unavailable or is removed from the host configuration. A stale saved_isc value can also survive after the KVM association is cleared and can cause a later cleanup to attempt another logical resource release. For the CVSS the PR:L value reflects that an attacker must control a guest or tenant with an assigned vfio ap mediated device and enable queue interrupt handling. The base impact is limited resource retention because one event leaks bounded resources and host configuration removal is an additional prerequisite. The paranoid availability impact is high only if automated or repeated queue assignment and removal can accumulate pinned pages or corrupt GISC registration accounting. No heap UAF, out of bounds access, information leak, or arbitrary write is established by the code change. Automated impact decision path. The original SimpleNet classifier selected MODERATE. The primary LLM estimated paranoid CVSS 4.7 and the production ActionableScore returned 2 with recommendation Ordinary Moderate. The production rules then evaluated CVSS thresholds and ActionableScore thresholds. Recorded rule transitions were CVSS and initial triage stage MODERATE to LOW because the CVSS score, vector or bug class threshold rule was applied. final reconciliation stage LOW to LOW because KP specialist did not establish a qualifying panic and the cross model evidence reconciliation rule was applied. 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. Exact triggered rule markers were DECREASED_TO_LOW_FROM_MODERATE_BASED_ON_GUESSCVSS_AND_CIANNH and KPANIC_UNSUPPORTED_REMOVED and V64_AEGIS_UNSUPPORTED_PROMOTION_BLOCKED. The independent weaker Aegis shadow evaluated CVSS 2.5 and ActionableScore 1 with primitive class CLASS_C and manual review REQUIRED. Its independently reconciled impact was MODERATE. The models disagreed but the aggregation rules retained the production result. The final reported impact is LOW.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate (with actual score 2)	MAYBE	INIT LEAK UAF HARDWARE LINUS TEST DECREASED_TO_LOW_FROM_MODERATE_BASED_ON_GUESSCVSS_AND_CIANNH KPANIC_UNSUPPORTED_REMOVED V64_AEGIS_UNSUPPORTED_PROMOTION_BLOCKED	-	-	checked

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

ActionableScore=2
PrimitiveClass=CLASS_C
RealUAF=NO
HostAdminRequired=UNKNOWN
NamespaceScopedPrivilege=NO
ImportantCandidate=NO
ManualReview=RECOMMENDED
AutoDowngradeAllowed=YES
RequiresHostUID0=UNKNOWN
AuthorizationDecisionBypass=NO
ProtectedResourceImpact=NONE
B4PendingReview=NO
B4PendingConfirmed=NO

1. ActionableScore

* Raw base score: 2.
* Conservative score: 2; no floor or cap applied.
* Raw paranoid score: 2.
* Paranoid score: 2; stronger consequences require an unproven accumulation or duplicate-unregister path.
* Final recommended bucket: **Ordinary Moderate**::

2. Signal breakdown

* +1 — Concrete persistent resource leak: unhandled `AP_RESPONSE_Q_NOT_AVAIL` leaves the KVM GISC registration and pinned NIB guest page unreleased.
* +1 — Weak invalid lifetime/resource state: when `kvm` is NULL, the old code leaves `saved_isc` valid, permitting a possible later duplicate logical release.
* No repeated-release bonus: the first actual GISC release and a reachable second `kvm_s390_gisc_unregister()` are not both demonstrated by the visible control flow.
* No crash/availability point: only WARN, bounded leakage per event, and potential accounting damage are shown.
* No UAF, heap OOB, arbitrary write, controlled reclaim, confidentiality, integrity, authorization bypass, or guest-to-host corruption is established.
* No race penalty: this is an ordered removal/cleanup sequence, not a proven narrow race.
* NEW52 B5-R does not apply: there is no retry-accumulated heap OOB write or later consumption of corrupted heap state.

3. Reachability analysis

A guest or tenant with an assigned VFIO-AP mediated device can enable queue interrupts, but queue removal from the host AP configuration is a separate host-side lifecycle operation. The evidence does not show that the guest can initiate that removal, so the complete trigger is compound and its effective privilege requirement remains unknown. No user-namespace or namespace-scoped capability path is involved. VFIO assignment and AP host configuration are prior administrative setup. No special timing is proven, although repeated harmful accumulation would require repeated host-side removal or reassignment activity not shown under attacker control.

4. Primitive and severity reading

The proven behavior is failure to release a pinned guest page and GISC registration, plus retention of a stale logical `saved_isc` value. This is resource leakage/invalid cleanup state, not a real heap UAF. The possible later “double-free” is not sufficiently grounded as a concrete second lifetime mutation: the old path skips unregister while `kvm` remains NULL, and the circumstances restoring a usable `kvm` and reaching duplicate unregister are not supplied.

Accordingly this is CLASS_C. Important-grade exploit leverage is not shown, so `ImportantCandidate=NO` and automatic Moderate handling remains permissible, though subsystem-specific review is advisable.

5. One-sentence report phrase

VFIO-AP queue removal can leak a pinned guest page and GISC registration and retain a stale ISC identifier, but no concrete UAF, OOB write, or attacker-controlled duplicate release is shown.

6. Manual review advice

MANUAL CHECK RECOMMENDED

Confirm whether mediated-device reuse can make the stale `saved_isc` reach a real duplicate GISC unregister or permit attacker-driven accumulation.

7. Call-site confidence

Call-site confidence: medium

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

Patch: s390/vfio-ap: fix KVM GISC and page leak when queue removed from host config
Commit: da69d3ac53490724eba0ade9deb4e539a6ae9034
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=da69d3ac53490724eba0ade9deb4e539a6ae9034

Commit description:

Three related problems exist in the handling of KVM interrupt and page
resources when a queue is removed from the host's AP configuration
while assigned to a mediated device (mdev).

Problem 1:
~~~~~~~~~
AP_RESPONSE_Q_NOT_AVAIL not handled in vfio_ap_mdev_reset_queue()

When the AP bus removes a queue device whose adapter or domain has
been removed from the host's AP configuration,
vfio_ap_mdev_remove_queue() is called. If the queue is still in the
host's AP configuration at that point, it calls
vfio_ap_mdev_reset_queue(), which issues a PQAP(ZAPQ). Since the
adapter is already gone from the host configuration, ap_zapq() returns
AP_RESPONSE_Q_NOT_AVAIL (0x01). This response code is not handled in
vfio_ap_mdev_reset_queue()'s switch statement and falls through to
the default case, which issues a WARN but does not call
vfio_ap_free_aqic_resources(). As a result, if IRQ handling was
enabled for the queue by the guest, the KVM GISC registration and
the pinned guest page holding the notification indicator byte (NIB)
are both leaked.

This is fixed by adding AP_RESPONSE_Q_NOT_AVAIL to the same case as
AP_RESPONSE_DECONFIGURED and AP_RESPONSE_CHECKSTOPPED in
vfio_ap_mdev_reset_queue(). Like those response codes, Q_NOT_AVAIL
indicates the queue is not operational and no further reset attempts
are possible; the correct action is to free the IRQ resources
immediately.

Problem 2:
~~~~~~~~~
 AP_RESPONSE_Q_NOT_AVAIL not handled in apq_status_check()

In vfio_ap_mdev_reset_queue(), there are four cases that indicate a queue
reset has not yet completed, in which case apq_reset_check() is queued to
a work queue to verify completion of the reset operation. This function
uses the PQAP(TAPQ) function to get the queue's status and calls
apq_status_check() to verify whether the reset has completed, failed or
needs to be executed again. As described in Problem #1 above,
apq_reset_check() does not specifically check for AP_RESPONSE_Q_NOT_AVAIL,
thereby potentially leaking KVM GISC registration and the pinned guest page
holding the NIB.

This is fixed by adding a case statement for AP_RESPONSE_Q_NOT_AVAIL to
apq_status_check() and returning -ENODEV for that case. The caller,
apq_reset_check() will then check for this return code and call
vfio_ap_free_aqic_resources() to prevent the leak.

Problem 3:
~~~~~~~~~
vfio_ap_free_aqic_resources() leaks saved_isc when kvm is NULL

vfio_ap_free_aqic_resources() guards the call to
kvm_s390_gisc_unregister() with:

    if (q->saved_isc != VFIO_AP_ISC_INVALID &&
        !WARN_ON(!(q->matrix_mdev && q->matrix_mdev->kvm)))

If matrix_mdev->kvm is NULL -- which can happen when
vfio_ap_mdev_unset_kvm() has already run and cleared kvm before a
subsequent cleanup path reaches this function -- the WARN_ON fires
and the entire block is skipped. This leaves q->saved_isc set to a
non-invalid value, creating a potential double-free on any subsequent
call to this function.

When kvm is NULL the KVM guest is already torn down, so
kvm_s390_gisc_unregister() need not and cannot be called; however,
q->saved_isc must always be cleared. Fix this by separating the
kvm_s390_gisc_unregister() call from the q->saved_isc reset. The
WARN_ON now guards only the genuinely impossible case of matrix_mdev
being NULL. A NULL kvm is handled gracefully by skipping only the
unregister call, and q->saved_isc = VFIO_AP_ISC_INVALID is set
unconditionally whenever saved_isc was not already invalid.

Additionally, add an else clause to the host-config check in
vfio_ap_mdev_remove_queue() to call vfio_ap_free_aqic_resources()
directly when the queue is not in the host's AP configuration. This
serves as a backstop: when the AP bus fires the driver .remove
callback after an adapter is removed from the host config, the queue
is by definition no longer addressable, so vfio_ap_mdev_reset_queue()

[Commit description truncated; see the upstream URL below]

Changed files:
  drivers/s390/crypto/vfio_ap_ops.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=da69d3ac53490724eba0ade9deb4e539a6ae9034

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

The original Linux kernel CVE announcement for CVE-2026-98473 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98473

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:L/UI:R/S:U/C:N/I:N/A:L
  The Best / paranoid CVSS vector: AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H
  The Best / paranoid CVSS score: 4.7

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: 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: 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).