[CVE-2026-68454][MODERATE 7.0] KVM: s390: pci: Fix handling of AIF enable without AISB

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

CVE: CVE-2026-68454
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: KVM: s390: pci: Fix handling of AIF enable without AISB
Commit: f887df91826e72b570c5e9298e66dd929f09edde
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=f887df91826e72b570c5e9298e66dd929f09edde
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-68454
Analysis date: Thu, 13 Aug 2026 11:04:29 -0400
ActionableScore: 6
ActionableScore lower bound: 4
Actionable bucket: Strong Important candidate / Actionable Moderate at minimum
Manual review required: YES

Summary:
KVM s390 PCI AIF setup can store an invalid GAITE AISB physical address when a guest enables AIF without a summary bit, potentially causing host DoS and requiring manual review for possible guest-to-host memory corruption impact.

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ABOUT THIS REPORT
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The original Linux kernel CVE announcement for CVE-2026-68454 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-68454

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: 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
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CVE-2026-68454	MODERATE	CHECK WITH IMPACT FROM ORIG NN MODERATE	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:H/PR:L/UI:N/S:C/C:H/I:H/A:H';**CWE-476;*CWE-20;CWE-754;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:C/C:N/I:L/A:H';BEST CVSS score: '7.8';DESCR 'KVM/s390 PCI interrupt forwarding can store an invalid guest AISB physical address when AIF is enabled without a summary bit. The vulnerable path derives the GAITE aisb value from page_address(NULL) instead of using zero for the missing AISB location. A malicious or misconfigured guest that can exercise the s390 PCI IRQ registration path may cause incorrect host side interrupt forwarding state. For the CVSS the PR:L is used because reliable triggering requires control over guest execution or guest PCI configuration, but not administrative privileges on the host. The issue is not directly network reachable. Impact is at least host denial of service and possible integrity impact from use of an invalid physical address. In the paranoid interpretation this is treated as a host memory corruption candidate because low level interrupt forwarding may later consume the bogus address.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Strong Important candidate / Actionable Moderate at minimum (with actual score 5)	YES	VIRT SIMPLEFIX HARDWARE LINUS  INCREASED_TO_HIGH_BASED_ON_GUESSCVSS LOWERED_FROM_HIGH_BASED_ON_NULLPTR DECREASED_TO_MODERATEREG_BASED_ON_FALSEPOSCHECKOFKP	NO	NO	checked

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ACTIONABLESCORE ANALYSIS
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ActionableScore=6
ActionableScoreLower=4

## 1. ActionableScore

* Conservative score: 4
* Paranoid score: 6
* Final recommended bucket: **Strong Important candidate / Actionable Moderate at minimum**::

## 2. Signal breakdown

Conservative signals:

* Local unprivileged or guest-triggered boundary input: +1. Triggering does not require host root, but does require control over a guest or guest PCI IRQ setup path.
* Memory corruption, weak/indirect corruption candidate: +1. The bug stores a bogus physical address derived from `page_address(NULL)` into GAITE state.
* Reliable host DoS concern: +1. Incorrect interrupt-forwarding state can plausibly crash or destabilize the host KVM path.
* Privileged kernel/device-management corruption path: +1. The corrupted state is in s390 KVM PCI interrupt forwarding, a highly trusted host/device-management context.
* Rare and configuration-dependent subsystem: -1. Requires s390 KVM PCI interrupt forwarding and a guest PCI/AIF setup path.
* Constrained or no attacker-controlled payload: -1. The stored bad address is not shown to be attacker-chosen arbitrary memory.

Paranoid additional signals:

* Weak LPE concern: +1. Guest-influenced invalid physical address state crosses the guest-to-host boundary and may later be consumed by low-level interrupt forwarding.
* Cross-boundary isolation concern: +1. The affected path is a KVM guest-to-host boundary, so host impact from guest-controlled configuration is security relevant.
* Integrity impact plausible: +1. If the bogus GAITE AISB address is used as a write/update target, host-side memory or interrupt state may be modified incorrectly.

Call-site confidence: medium. The patch shows the bad GAITE assignment directly, but not the later hardware or interrupt-forwarding consumers of `gaite->aisb`.

## 3. Reachability analysis

The likely attacker is a malicious or misconfigured guest with access to the s390 PCI IRQ registration path. This is not network reachable. It does not require host administrative privileges, but it does require a VM environment with s390 KVM PCI interrupt forwarding and a suitable assigned or virtual PCI device path. Containers and namespaces on the host are not the main factor here. The practical exposure is narrow, but the guest-to-host boundary makes the issue more important than an ordinary local driver bug.

## 4. Severity interpretation

This is not demonstrated arbitrary code execution and not a proven strong LPE primitive. The realistic impact is host DoS or incorrect host-side interrupt-forwarding state. The paranoid interpretation treats it as an actionable KVM boundary issue because a guest-controlled path can cause an invalid physical address to be stored in trusted host interrupt state. Therefore it should be handled as Actionable Moderate at minimum, with Strong Important candidate consideration if later review confirms that the bogus AISB address can cause host memory corruption.

## 5. One-sentence report phrase

KVM s390 PCI AIF setup can store an invalid GAITE AISB physical address when a guest enables AIF without a summary bit, potentially causing host DoS and requiring manual review for possible guest-to-host memory corruption impact.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED.
YES REQUIRES MANUAL CHECK because this is a KVM guest-to-host boundary issue involving an invalid physical address stored in trusted interrupt-forwarding state, with plausible but not fully demonstrated host integrity impact.

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UPSTREAM PATCH SUMMARY
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Patch: KVM: s390: pci: Fix handling of AIF enable without AISB
Commit: f887df91826e72b570c5e9298e66dd929f09edde
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=f887df91826e72b570c5e9298e66dd929f09edde

Commit description:

When a guest seeks to register IRQs without a summary bit specified,
ensure that the associated GAITE then stores 0 for the guest AISB
location instead of virt_to_phys(page_address(NULL)).

Fixes: 3c5a1b6 ("KVM: s390: pci: provide routines for enabling/disabling interrupt forwarding")
Cc: stable@vger.kernel.org
Reviewed-by: Farhan Ali <alifm@linux.ibm.com>
Signed-off-by: Matthew Rosato <mjrosato@linux.ibm.com>
Signed-off-by: Christian Borntraeger <borntraeger@linux.ibm.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  arch/s390/kvm/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=f887df91826e72b570c5e9298e66dd929f09edde

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

The original Linux kernel CVE announcement for CVE-2026-68454 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-68454

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:N/S:C/C:N/I:L/A:H
  The Best / paranoid CVSS vector: AV:L/AC:H/PR:L/UI:N/S:C/C:H/I:H/A:H
  The Best / paranoid CVSS score: 7.8

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: 6

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 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).