[CVE-2026-52968][IMPORTANT] KVM: s390: pci: fix GAIT table indexing due to double-scaling pointer arithmetic

[CVE-2026-52968][IMPORTANT] KVM: s390: pci: fix GAIT table indexing due to double-scaling pointer arithmetic

[AL-KERNEL]

CVE: CVE-2026-52968
Priority: IMPORTANT
AL-KERNEL base severity: IMPORTANT
KPANIC flag: YES
Patch: KVM: s390: pci: fix GAIT table indexing due to double-scaling pointer arithmetic
Commit: 31a9d9f9942885aae356a1a57c79e82c5b5b0828
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=31a9d9f9942885aae356a1a57c79e82c5b5b0828
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-52968
Analysis date: Wed, 24 Jun 2026 15:32:03 -0400
ActionableScore: 7
ActionableScore lower bound: 5
Actionable bucket: Strong Important candidate / Actionable Moderate at minimum
Manual review required: YES

Summary:
A double-scaled GAIT table index in KVM s390 PCI interrupt forwarding can cause host kernel out-of-bounds access when zPCI adapter interrupt forwarding is used, making this at least a host DoS risk and a manual-review memory corruption candidate.

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

The original Linux kernel CVE announcement for CVE-2026-52968 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-52968

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: IMPORTANT
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-2026-52968	IMPORTANT	CHECK	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H';*CWE-787;CWE-125;CWE-682;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:L/A:H';BEST CVSS score: '7';DESCR 'KVM s390 PCI interrupt forwarding indexes the GAIT table incorrectly because pointer arithmetic on a struct zpci_gaite pointer is combined with an extra sizeof(struct zpci_gaite) multiplier. This makes aisb select element aisb times 16 instead of aisb and can access memory outside the GAIT table when aisb is 32 or higher with 512 zPCI device slots. The affected paths enable or disable adapter interrupt forwarding and forward Adapter Event Notifications, so the bug can produce out of bounds reads and writes in host kernel memory. For the CVSS the PR:L is used in the paranoid score because a lower privileged VM owner or guest context with access to a configured s390 zPCI device may be enough to exercise the vulnerable KVM path, while reliable triggering depends on the host zPCI and passthrough configuration. The issue is not reachable from the external network and requires local or guest access to a KVM s390 environment. Impact is at least denial of service and in worst case may allow confidentiality or integrity impact due to host kernel memory corruption. YES REQUIRES MANUAL CHECK';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Strong Important candidate / Actionable Moderate at minimum (with actual score 7)	YES	OOB VIRT SIMPLEFIX HARDWARE LINUS  KPANIC INCREASED_TO_MODERATE7_BASED_ON_GUESSCVSS KPANIC INCREASED_TO_HIGH_BASED_ON_ACTIONABLESCOREHIGHEREQTHAN7	NO	NO	checked

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ACTIONABLESCORE ANALYSIS
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ActionableScore=7
ActionableScoreLower=5

## 1. ActionableScore

* Conservative score: 5
* Paranoid score: 7
* Final recommended bucket: **Strong Important candidate / Actionable Moderate at minimum**::

## 2. Signal breakdown

Conservative signals:

* Local or guest-triggerable path: +1. The affected KVM s390 PCI paths can be exercised from a local virtualization context when zPCI is configured for a guest.
* Constrained kernel memory corruption candidate: +1. The bug causes out-of-bounds GAIT table access, but the exact overwritten fields and payload appear constrained by kernel-side GAIT metadata operations.
* Privileged kernel/device-management memory corruption path: +1. The corruption occurs in KVM host-side PCI interrupt forwarding code.
* Reliable kernel crash / strong DoS: +1. Out-of-bounds access in host kernel memory can plausibly crash the host.
* Integrity impact plausible: +1. At least one affected path modifies the selected GAIT entry, so an out-of-bounds write is plausible.
* Rare/difficult-to-reach subsystem/configuration: -1. Requires s390 KVM with zPCI and adapter interrupt forwarding/AEN conditions.

Paranoid additions/interpretation:

* Generic memory corruption: +2 instead of constrained +1. The patch explicitly fixes out-of-bounds accesses, including write-like operations on host kernel memory.
* Weak LPE concern: +1. Host-side KVM memory corruption could theoretically become more than DoS, although no controlled overwrite or reclaim primitive is shown.
* Confidentiality impact plausible: +1. OOB reads of adjacent kernel memory are possible in principle, but no disclosure path is demonstrated.
* Integrity impact plausible: +1. OOB writes to adjacent kernel memory are directly plausible.

## 3. Reachability analysis

The bug is not remotely network reachable. Realistic triggering requires an s390 KVM environment with zPCI devices and interrupt forwarding or Adapter Event Notification paths in use. A full host root user is not necessarily required in the practical risk model if a guest or VM owner can exercise the assigned zPCI device path, but host configuration must first expose the relevant device functionality. Namespaces do not materially lower reachability for ordinary local users because this is a KVM and hardware-assisted PCI virtualization path, not a generic namespaced syscall surface. Exposure is therefore narrow, but the affected code runs in the host kernel and crosses a guest-to-host trust boundary.

## 4. Severity interpretation

This is more than an ordinary Moderate because the patch fixes concrete out-of-bounds accesses in KVM host-side code. Conservative handling treats it as Actionable Moderate due to constrained corruption and rare s390 zPCI exposure. Paranoid handling reaches Strong Important candidate because host kernel OOB access in a virtualization boundary can have confidentiality, integrity, and availability consequences even when a practical privilege-escalation primitive is not demonstrated. Theoretical memory corruption potential is real. Realistic exploitation evidence beyond crash or host memory corruption is not shown in the patch.

## 5. One-sentence report phrase

A double-scaled GAIT table index in KVM s390 PCI interrupt forwarding can cause host kernel out-of-bounds access when zPCI adapter interrupt forwarding is used, making this at least a host DoS risk and a manual-review memory corruption candidate.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED

This should not be auto-closed because it is an out-of-bounds access in KVM host-side code across a guest or VM boundary, even though practical exploitation depends on s390 zPCI configuration and the overwrite primitive appears constrained.

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

Patch: KVM: s390: pci: fix GAIT table indexing due to double-scaling pointer arithmetic
Commit: 31a9d9f9942885aae356a1a57c79e82c5b5b0828
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=31a9d9f9942885aae356a1a57c79e82c5b5b0828

Commit description:

kvm_s390_pci_aif_enable(), kvm_s390_pci_aif_disable(), and
aen_host_forward() index the GAIT by manually multiplying the index
with sizeof(struct zpci_gaite).

Since aift->gait is already a struct zpci_gaite pointer, this
double-scales the offset, accessing element aisb*16 instead of aisb.

This causes out-of-bounds accesses when aisb >= 32 (with
ZPCI_NR_DEVICES=512)

Fix by removing the erroneous sizeof multiplication.

Fixes: 3c5a1b6 ("KVM: s390: pci: provide routines for enabling/disabling interrupt forwarding")
Fixes: 73f91b0 ("KVM: s390: pci: enable host forwarding of Adapter Event Notifications")
Reported-by: Yuhao Jiang <danisjiang@gmail.com>
Cc: stable@vger.kernel.org
Signed-off-by: Junrui Luo <moonafterrain@outlook.com>
Reviewed-by: Christian Borntraeger <borntraeger@linux.ibm.com>
Reviewed-by: Matthew Rosato <mjrosato@linux.ibm.com>
Tested-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/interrupt.c
  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=31a9d9f9942885aae356a1a57c79e82c5b5b0828

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

The original Linux kernel CVE announcement for CVE-2026-52968 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-52968

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:U/C:L/I:L/A:H
  The Best / paranoid CVSS vector: AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H
  The Best / paranoid CVSS score: 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: 5
  Paranoid ActionableScore: 7

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: IMPORTANT
KPANIC detected for this report: YES
Published priority for this report (same as in Subject): IMPORTANT

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).