[CVE-2026-80895][MODERATE 7.0] mshv: Order pt_vp_array publish against irqfd assertion path [ Upstream

[CVE-2026-80895][MODERATE 7.0] mshv: Order pt_vp_array publish against irqfd assertion path [ Upstream

[AL-KERNEL]

CVE: CVE-2026-80895
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: mshv: Order pt_vp_array publish against irqfd assertion path [ Upstream
Commit: 062aa5dcc49a9ad96726a80c2a0ab0a1233bc2b9
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=062aa5dcc49a9ad96726a80c2a0ab0a1233bc2b9
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-80895
Analysis date: Fri, 04 Sep 2026 15:25:42 -0400
ActionableScore: 5
ActionableScore lower bound: 3
Actionable bucket: Actionable Moderate at minimum
Manual review required: NO

Summary:
A local mshv user can race irqfd assertion with VP creation so the irqfd fast path observes a non NULL VP pointer before initialization is fully visible, which may cause incorrect hypervisor state use or host kernel DoS on weakly ordered architectures.

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

The original Linux kernel CVE announcement for CVE-2026-80895 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-80895

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-2026-80895	MODERATE	https://www.kernelcve.org/list/?q=CVE-2026-80895 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-362;CWE-667;CWE-665;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '5.8';DESCR 'A race in the mshv irqfd fast path can allow mshv_try_assert_irq_fast() to observe a non NULL VP pointer while mshv_partition_ioctl_create_vp() is still publishing the newly initialized VP state. On weakly-ordered architectures this can expose partially initialized fields such as vp_register_page to a lockless reader and may cause incorrect interrupt delivery, VMM failure, or a host kernel denial of service. For the CVSS the PR:L value is used because triggering requires local access to /dev/mshv and the ability to create VP and irqfd state, but this may be available to a VMM process or a reduced capability service account rather than full host administrator access. The issue is not network reachable and is triggered through local mshv device operations. Impact is at least local denial of service. In the worst still-defensible case it may allow limited confidentiality or integrity impact because a partially initialized kernel object is consumed in a hypervisor fast path, so manual review is recommended.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate at minimum (with actual score 4)	YES	INIT RACE HARDWARE  INCREASED_FROM_LOW_BASED_ON_REQUIREMANUALCHECK DECREASED_TO_MODERATEREG_BASED_ON_FALSEPOSCHECKOFKP	YES	NO	checked

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

ActionableScore=5
ActionableScoreLower=3

## 1. ActionableScore

* Conservative score: 3
* Paranoid score: 5
* Final recommended bucket: **Actionable Moderate at minimum**::

## 2. Signal breakdown

Conservative signals:

* Local trigger: +1. Triggering requires local access to `/dev/mshv` and the ability to create VP and irqfd state.
* Weak or indirect corruption candidate: +1. The reader can observe a non NULL VP pointer before initialization stores are visible, causing use of a partially initialized kernel object.
* Reliable kernel crash or strong DoS concern: +1. Use of fields such as `vp_register_page` before visible initialization can plausibly cause VMM failure or host kernel DoS.
* Hard race or special timing required: -1. The bug requires concurrent `MSHV_IRQFD` assertion and `MSHV_CREATE_VP`.
* Rare or configuration dependent subsystem: +0. `mshv` is not a broad default subsystem, but it is reachable through an ordinary local device interface when enabled.

Paranoid additional signals:

* Privileged kernel or hypervisor device-management path: +1. The affected object is a VP in a hypervisor-facing kernel driver path.
* Confidentiality impact plausible: +1. Limited C impact is defensible only as a worst-case concern from consuming partially initialized hypervisor state.
* Integrity impact plausible: +1. Limited I impact is defensible only as a worst-case concern from incorrect interrupt delivery or corrupted VP state use.
* No strong LPE signal awarded. The patch does not show UAF reclaim, object replacement, write-after-free, callback control, type confusion, refcount takeover, or arbitrary write.

## 3. Reachability analysis

The bug is locally reachable by a process that can access `/dev/mshv` and create both irqfd and VP state. This is not a network reachable path. The realistic attacker is a VMM process, service account, reduced capability root, or another local actor delegated access to the MSHV interface. Full host root should not automatically be assumed because VMM service accounts may be capability separated.

The race is structurally plausible because `MSHV_IRQFD` does not require the target `lapic_apic_id` to already refer to an existing VP. A user can register an irqfd for a not yet created VP and then race eventfd wakeup against `MSHV_CREATE_VP`. The issue is mainly relevant on weakly ordered architectures. On x86 TSO the acquire and release operations compile to plain accesses, which lowers practical exposure there.

## 4. Severity interpretation

This behaves more like an Actionable Moderate than ordinary Low or auto-close Moderate. The demonstrated primitive is a memory ordering race leading to consumption of a partially initialized kernel object, not a confirmed UAF or arbitrary write. Realistic impact is local DoS or VMM failure. The paranoid score reaches 5 because the object is consumed in a hypervisor fast path and limited confidentiality or integrity impact cannot be fully excluded without deeper source review.

It is not a Strong Important candidate from the supplied patch alone because the destroy-side lifetime issue is explicitly out of scope and the patch does not demonstrate attacker-controlled reclaim, stale object reuse, write primitive, or privilege escalation.

## 5. One-sentence report phrase

A local mshv user can race irqfd assertion with VP creation so the irqfd fast path observes a non NULL VP pointer before initialization is fully visible, which may cause incorrect hypervisor state use or host kernel DoS on weakly ordered architectures.

## 6. Manual review recommendation

MANUAL CHECK RECOMMENDED

Reason: this is a race and memory ordering bug in a hypervisor device path. The current evidence supports DoS and limited worst-case C/I concern, but not confirmed privilege escalation or strong memory corruption.

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

Patch: mshv: Order pt_vp_array publish against irqfd assertion path [ Upstream
Commit: 062aa5dcc49a9ad96726a80c2a0ab0a1233bc2b9
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=062aa5dcc49a9ad96726a80c2a0ab0a1233bc2b9

Changed files:
  drivers/hv/mshv_eventfd.c
  drivers/hv/mshv_root_main.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=062aa5dcc49a9ad96726a80c2a0ab0a1233bc2b9

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

The original Linux kernel CVE announcement for CVE-2026-80895 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-80895

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: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: 3
  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: 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).