From mboxrd@z Thu Jan 1 00:00:00 1970 From: AL-KERNEL To: kernel-cve@kernelcve.org Subject: [CVE-2026-46316][MODERATE 7.0] KVM: arm64: vgic-its: Drop the translation cache reference only for the erased entry Date: Tue, 09 Jun 2026 08:53:33 -0400 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-AL-KERNEL-CVE: CVE-2026-46316 X-AL-KERNEL-Priority: MODERATE 7.0 X-AL-KERNEL-Severity: MODERATE 7.0 X-AL-KERNEL-Base-Severity: MODERATE X-AL-KERNEL-KPANIC: YES X-AL-KERNEL-ActionableScore: 5 X-AL-KERNEL-ActionableScore-Lower: 4 X-AL-KERNEL-Commit: b7b72e88046328c9fdc638fe887d4240257dd5dc List-Id: 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. ====================================================================== 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. ====================================================================== 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 ====================================================================== 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 Reviewed-by: Oliver Upton Link: https://patch.msgid.link/ah2c5lu4JbUg7dj-@v4bel Signed-off-by: Marc Zyngier Cc: stable@vger.kernel.org Signed-off-by: Greg Kroah-Hartman 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).