[CVE-2026-80699][MODERATE REGULAR] KVM: arm64: vgic: Avoid double-deactivate of IRQs in the nested context

[CVE-2026-80699][MODERATE REGULAR] KVM: arm64: vgic: Avoid double-deactivate of IRQs in the nested context

[AL-KERNEL]

CVE: CVE-2026-80699
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: KVM: arm64: vgic: Avoid double-deactivate of IRQs in the nested context
Commit: f78f08b38a7f121c7d6b3e41002d9de7fd3c9189
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=f78f08b38a7f121c7d6b3e41002d9de7fd3c9189
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-80699
Analysis date: Fri, 28 Aug 2026 06:49:15 -0400
ActionableScore: 4
ActionableScore lower bound: 3
Actionable bucket: Borderline manual review recommended / Actionable Moderate at minimum
Manual review required: YES

Summary:
A guest-influenced nested KVM VGIC path on affected AmpereOne CPUs can double deactivate a physical interrupt and trigger an erratum that loses pending interrupt state, causing host or CPU availability degradation without evidence of memory corruption or privilege escalation.

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ABOUT THIS REPORT
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The original Linux kernel CVE announcement for CVE-2026-80699 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-80699

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
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CVE-2026-80699	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:N/I:N/A:H';CWE-754;CWE-703;*CWE-664;BEST CVSS score: '5.6';DESCR 'KVM arm64 VGICv3 can double deactivate a physical interrupt in nested virtualization state because the interrupt was already deactivated through the HW bit in the LR. On affected AmpereOne CPUs this can hit an erratum where deactivating a non active interrupt that is still the highest priority pending interrupt can lose the pending state and prevent future interrupt delivery. For the CVSS the PR:L is used because practical triggering requires access to run or influence a guest workload rather than full host administrator privileges. The issue is not directly network reachable and depends on KVM arm64 nested virtualization on affected AmpereOne hardware. Impact is denial of service through broken interrupt delivery or host responsiveness degradation, with no supported evidence of memory corruption, information disclosure, or privilege escalation.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Borderline manual review recommended / Actionable Moderate at minimum (with actual score 4)  SKIP CVE-2026-80699 UNKNOWN SKIP The Fixes patch not applied yet, so unlikely that actual: url YES  NO NO unknown 	MAYBE	DANGER VIRT SIMPLEFIX HARDWARE LINUS  DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN5	-	-	checked

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ACTIONABLESCORE ANALYSIS
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ActionableScore=4
ActionableScoreLower=3

## 1. ActionableScore

* Conservative score: 3
* Paranoid score: 4
* Final recommended bucket: **Borderline manual review recommended / Actionable Moderate at minimum**

## 2. Signal breakdown

Triggered signals:

* Local unprivileged trigger: +1. A guest or tenant-controlled workload can plausibly influence virtual interrupt state without full host-root privileges.
* Reliable kernel crash / strong DoS: +1. The erratum can cause interrupt pending state loss and prevent future interrupt delivery.
* Availability impact realistic: +1. The impact can extend beyond a transient warning because interrupt delivery may remain broken.
* Cross-boundary isolation/policy concern: +1 in paranoid scoring. The effect crosses from guest-controlled execution into host CPU interrupt delivery behavior.
* Broad/default/common subsystem: +1 in paranoid scoring. KVM is a common virtualization subsystem, though this specific path is narrower.

Negative signals:

* Physical-only or rare hardware-only condition: -2. The issue depends on AmpereOne errata AC03_CPU_57 or AC04_CPU_29.
* Legacy / non-default execution mode: -1. The affected behavior requires nested KVM VGIC state, which is not the most common virtualization mode.

No memory corruption, UAF, arbitrary write, info leak, or privilege escalation primitive is supported by the patch.

## 3. Reachability analysis

The likely trigger is a guest-controlled or tenant-controlled KVM workload on arm64 with nested virtualization enabled. Full host administrator privileges are not necessarily required in virtualized hosting models, so PR:L is reasonable for CVSS-style reasoning. The issue is not directly network reachable. Network activity could only matter indirectly if it influences guest interrupt behavior.

The affected configuration is narrow. It requires AmpereOne hardware affected by the documented errata and the nested VGIC path. This makes broad exposure limited, but the guest-to-host availability boundary makes the issue unsuitable for automatic closure without review.

## 4. Severity interpretation

This behaves more like a hardware-specific KVM availability issue than a generic kernel memory corruption vulnerability. The realistic demonstrated impact is DoS through broken interrupt delivery or host responsiveness degradation. There is no evidence of confidentiality impact, integrity impact, UAF, object reuse, type confusion, or LPE.

Because the bug crosses a virtualization boundary and affects interrupt delivery on specific CPUs, it is stronger than an ordinary low-risk compatibility fix. It is best treated as borderline to actionable Moderate, not an Important memory-corruption candidate.

## 5. One-sentence report phrase

A guest-influenced nested KVM VGIC path on affected AmpereOne CPUs can double deactivate a physical interrupt and trigger an erratum that loses pending interrupt state, causing host or CPU availability degradation without evidence of memory corruption or privilege escalation.

## 6. Manual review recommendation

YES REQUIRES MANUAL CHECK

MANUAL CHECK RECOMMENDED. The issue is hardware-specific and DoS-only, but it crosses the KVM guest-to-host boundary and can affect host interrupt delivery, so it should not be auto-closed purely as a low-risk erratum workaround.

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

Patch: KVM: arm64: vgic: Avoid double-deactivate of IRQs in the nested context
Commit: f78f08b38a7f121c7d6b3e41002d9de7fd3c9189
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=f78f08b38a7f121c7d6b3e41002d9de7fd3c9189

Commit description:

In the nested state, the physical interrupt has already been
deactivated through the HW bit in the LR. The extra deactivation
would be harmless but can hit an errata case on AmpereOne, so
avoid it here.

On AmpereOne, deactivating a physical interrupt through
ICC_DIR_EL1 or ICC_EOIR1_EL1 (depending on EOImode) which is not
active, but is the highest priority pending interrupt causes the
cpu to lose the interrupt pending state and also prevents the
delivery of future interrupts.

Fixes: 6dd333c ("KVM: arm64: GICv3: nv: Plug L1 LR sync into deactivation primitive")
Signed-off-by: D Scott Phillips <scott@os.amperecomputing.com>
Cc: stable@vger.kernel.org
Link: https://lore.kernel.org/linux-arm-kernel/20260710222128.416581-1-scott@os.amperecomputing.com/
Link: https://patch.msgid.link/20260714231158.496808-1-scott@os.amperecomputing.com
Signed-off-by: Marc Zyngier <maz@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  kernel/20260710222128.416581-1-scott
  arch/arm64/silicon-errata.rst
  arch/arm64/kvm/vgic/vgic-v3.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=f78f08b38a7f121c7d6b3e41002d9de7fd3c9189

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

The original Linux kernel CVE announcement for CVE-2026-80699 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-80699

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: Not available
  The Best / paranoid CVSS vector: AV:L/AC:H/PR:L/UI:N/S:C/C:N/I:N/A:H
  The Best / paranoid CVSS score: 5.6

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: 3
  Paranoid ActionableScore: 4

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).