[CVE-2026-46316][MODERATE 7.0] KVM: arm64: vgic-its: Drop the translation cache reference only for the erased entry

[CVE-2026-46316][MODERATE 7.0] KVM: arm64: vgic-its: Drop the translation cache reference only for the erased entry

[AL-KERNEL]

CVE: CVE-2026-46316
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: KVM: arm64: vgic-its: Drop the translation cache reference only for the erased entry
Commit: b7b72e88046328c9fdc638fe887d4240257dd5dc
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=b7b72e88046328c9fdc638fe887d4240257dd5dc
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-46316
Analysis date: Tue, 09 Jun 2026 08:53:33 -0400
ActionableScore: 5
ActionableScore lower bound: 4
Actionable bucket: Strong Important candidate / Actionable Moderate at minimum
Manual review required: YES

Summary:
A race in KVM arm64 VGIC ITS translation cache invalidation can double-drop a cache reference and leave an ITE pointing to a freed `vgic_irq` object, creating a guest-reachable host-kernel UAF with at least DoS impact and possible guest-to-host security impact.

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

The original Linux kernel CVE announcement for CVE-2026-46316 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-46316

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
======================================================================

CVE-2026-46316	MODERATE	CHECK	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-362;*CWE-416;CWE-415;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:C/C:L/I:L/A:H';BEST CVSS score: '7.8';DESCR 'A race in KVM/arm64 VGIC ITS translation cache invalidation can drop the same cache reference more than once when concurrent invalidation paths observe the same xarray entry. This can free a vgic IRQ object while an ITE still maps it, creating a host kernel use-after-free condition. For the CVSS the PR:L value is used because a malicious guest or VM tenant needs access to a KVM arm64 VM with vGIC ITS enabled, but no host administrator privileges are required. The issue is not directly network reachable and is triggered through guest controlled virtual interrupt controller state rather than packet traffic. Impact is at least a local denial of service via host kernel crash and in worst case may allow confidentiality or integrity impact due to host memory corruption. For the paranoid score, choose the highest still defensible interpretation supported by the bug class and patch context, with preference for manual-review sensitivity over autoclosed false negatives.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Strong Important candidate / Actionable Moderate at minimum (with actual score 5)	YES	VIRT UAF HARDWARE LINUS KPANIC  KPANIC INCREASED_TO_HIGH_BASED_ON_GUESSCVSS KPANIC DECREASED_TO_MODERATE70_BASED_ON_ACTIONABLESCORELOWERTHAN7	YES	NO	guess

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

ActionableScore=5
ActionableScoreLower=4

## 1. ActionableScore

* Conservative score: **4**
* Paranoid score: **5**
* Final recommended bucket: **Strong Important candidate / Actionable Moderate at minimum**::

## 2. Signal breakdown

Conservative signals:

* **Local unprivileged trigger: +1**
  A malicious guest or VM tenant with access to a KVM arm64 VM can plausibly influence VGIC ITS state without host administrator privileges.

* **Memory corruption, weak primitive: +1**
  The patch describes a race that can drop the same cache reference more than once, allowing a `vgic_irq` object to be freed while still referenced by an ITE. This is a real UAF candidate, but the patch does not show attacker-controlled reclaim, overwrite, callback control, or object replacement.

* **Real lifetime corruption: +1**
  This is a reference lifetime bug: the same cache reference can be released multiple times under concurrent invalidation.

* **Reliable kernel crash / strong DoS: +1**
  A freed IRQ object still reachable from VGIC ITS mappings can plausibly cause host kernel crash or KVM failure.

* **Hard or unreliable race: -1**
  Triggering requires concurrent cache invalidation paths, so timing is non-trivial.

* **KVM virtualization boundary exposure: +1**
  The bug is in host KVM code reachable from guest-controlled virtual interrupt controller behavior. This is not network-reachable, but it crosses an important guest-to-host trust boundary.

Conservative total: **4**

Paranoid adjustment:

* **Weak LPE concern: +1**
  Because the UAF occurs in host KVM memory and the stale object can remain mapped through an ITE, guest-to-host impact deserves manual review even though no concrete reclaim or write primitive is demonstrated.

Paranoid total: **5**

## 3. Reachability analysis

The issue is not directly network reachable. It is reachable through KVM on arm64 when a guest uses VGIC ITS functionality and can cause concurrent invalidation paths to act on the same per-ITS translation cache entry.

The practical attacker is a local VM tenant, malicious guest, or local user with access to create or control a KVM VM. This should not be treated as PR:H in practical triage, because host administrator privileges are not required once KVM access is granted. Namespaces do not directly make this bug reachable, but containerized or delegated virtualization setups can lower the practical barrier if `/dev/kvm` is exposed.

The path is configuration-dependent on arm64 KVM with VGIC ITS, but this is a normal virtualization feature rather than an obscure debug-only path.

## 4. Severity interpretation

This is stronger than an ordinary Moderate because it is a real host-kernel lifetime bug in a guest-reachable KVM path. The realistic demonstrated impact is likely host crash or KVM DoS. The theoretical risk is higher because a double put can create a UAF while another ITS mapping still references the freed object.

However, the patch does not demonstrate attacker-controlled reclaim, write-after-free, type confusion, callback dispatch, or arbitrary write. Therefore the conservative score should remain below Important by default, while the paranoid score should be treated as **Actionable Moderate** and manually reviewed for guest-to-host escalation potential.

## 5. One-sentence report phrase

A race in KVM arm64 VGIC ITS translation cache invalidation can double-drop a cache reference and leave an ITE pointing to a freed `vgic_irq` object, creating a guest-reachable host-kernel UAF with at least DoS impact and possible guest-to-host security impact.

## 6. Manual review recommendation

**MANUAL CHECK REQUIRED**

This is a KVM guest-to-host lifetime corruption issue with a plausible UAF in host kernel memory. Even though no concrete exploit primitive is shown, the affected trust boundary and object lifetime pattern are important enough to avoid auto-closure.

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

Patch: KVM: arm64: vgic-its: Drop the translation cache reference only for the erased entry
Commit: b7b72e88046328c9fdc638fe887d4240257dd5dc
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=b7b72e88046328c9fdc638fe887d4240257dd5dc

Commit description:

vgic_its_invalidate_cache() walks the per-ITS translation cache with
xa_for_each() and drops the cache's reference on each entry with
vgic_put_irq(). It puts the iterated pointer, though, rather than the
value returned by xa_erase().

The function is called from contexts that do not exclude one another: the
ITS command handlers hold its_lock, the GITS_CTLR write path holds
cmd_lock, and the path that clears EnableLPIs in a redistributor's
GICR_CTLR holds neither. Two or more of them can drain the same cache
concurrently, and if each one observes the same entry, erases it and then
puts it, the single reference the cache holds on that entry is dropped
more than once. The entry can then be freed while an ITE still maps it.

xa_erase() is atomic and returns the previous entry, so put only the entry
that this context actually removed. The cache reference is then dropped
exactly once per entry even when the invalidations run concurrently, and
the behavior is unchanged when only one context runs.

Fixes: 8201d10 ("KVM: arm64: vgic-its: Maintain a translation cache per ITS")
Signed-off-by: Hyunwoo Kim <imv4bel@gmail.com>
Reviewed-by: Oliver Upton <oupton@kernel.org>
Link: https://patch.msgid.link/ah2c5lu4JbUg7dj-@v4bel
Signed-off-by: Marc Zyngier <maz@kernel.org>
Cc: stable@vger.kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  arch/arm64/kvm/vgic/vgic-its.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=b7b72e88046328c9fdc638fe887d4240257dd5dc

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

The original Linux kernel CVE announcement for CVE-2026-46316 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-46316

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:L/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: 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: YES
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).