From mboxrd@z Thu Jan 1 00:00:00 1970 From: AL-KERNEL To: kernel-cve@kernelcve.org Subject: [CVE-2026-98472][LOW] KVM: SEV: Free have_run_cpus during VM destruction even if VM is no longer SEV Date: Sat, 24 Oct 2026 06:33:53 -0400 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-AL-KERNEL-CVE: CVE-2026-98472 X-AL-KERNEL-Priority: LOW X-AL-KERNEL-Severity: LOW X-AL-KERNEL-Base-Severity: LOW X-AL-KERNEL-KPANIC: NO X-AL-KERNEL-ActionableScore: 1 X-AL-KERNEL-ActionableScore-Lower: unknown X-AL-KERNEL-Commit: 6aef7cf800098749ff5d660222efaf6e01e98c09 List-Id: CVE: CVE-2026-98472 Priority: LOW AL-KERNEL base severity: LOW KPANIC flag: NO Patch: KVM: SEV: Free have_run_cpus during VM destruction even if VM is no longer SEV Commit: 6aef7cf800098749ff5d660222efaf6e01e98c09 Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=6aef7cf800098749ff5d660222efaf6e01e98c09 Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98472 Analysis date: Sat, 24 Oct 2026 06:33:53 -0400 ActionableScore: 1 ActionableScore lower bound: unknown Actionable bucket: Ordinary Moderate Manual review required: NO Summary: SEV intra-host migration can leave `have_run_cpus` permanently allocated when the converted source VM is destroyed, allowing repeated privileged VM lifecycle operations to accumulate kernel memory. ====================================================================== ABOUT THIS REPORT ====================================================================== The original Linux kernel CVE announcement for CVE-2026-98472 is available here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98472 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: LOW 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-2026-98472 LOW https://www.kernelcve.org/list/?q=CVE-2026-98472 CHECK WITH IMPACT FROM ORIG NN MODERATE | AEGIS IMPACT MODERATE AEGIS_AS=1 LEGACY=LOW RESULT=DIFF (final Legacy and Aegis differ; FINAL: LOW, Aegis: MODERATE) Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H';*CWE-401;CWE-404;*CWE-772;Other CVSS 'AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:L';BEST CVSS score: '5.5';DESCR 'An SEV VM can become a non SEV source VM after intra host migration while retaining its allocated have_run_cpus cpumask. VM destruction then returns before freeing the mask, causing a persistent kernel memory leak for each completed migration and destruction sequence. For the CVSS the PR:L value reflects that an attacker needs a local process with access to KVM VM file descriptors and control over SEV intra host migration. The issue is not directly reachable from a guest or the network. No UAF, invalid dereference, OOB access, or memory corruption primitive is demonstrated. Availability impact is normally low, although sustained repetition could eventually cause host memory pressure or exhaustion. Automated impact decision path. The original SimpleNet classifier selected MODERATE_KPANIC. The primary LLM estimated paranoid CVSS 5.5 and the production ActionableScore returned 1 with recommendation Ordinary Moderate. The production rules then evaluated CVSS thresholds and ActionableScore thresholds. Recorded rule transitions were CVSS and initial triage stage MODERATE_KPANIC to MODERATE because the CVSS score, vector or bug class threshold rule was applied. ActionableScore thresholds stage MODERATE to LOW because the ActionableScore threshold rule was applied. final reconciliation stage LOW to LOW because KP specialist did not establish a qualifying panic and the cross model evidence reconciliation rule was applied. The legacy KP specialist has no review artifact for this run. The legacy FD or DH downgrade specialist has no review artifact for this run. Exact triggered rule markers were DECREASED_TO_MODERATE_REGULAR_FROM_MODERATE7_BASED_ON_GUESSCVSS_AND_CIANNH and DECREASED_TO_LOW_FROM_MODERATE_BASED_ON_ACTIONABLESCORELESSTHAN3 and KPANIC_UNSUPPORTED_REMOVED and V64_AEGIS_UNSUPPORTED_PROMOTION_BLOCKED. The independent weaker Aegis shadow evaluated CVSS 3.3 and ActionableScore 1 with primitive class CLASS_C and manual review REQUIRED. Its independently reconciled impact was MODERATE. The models disagreed but the aggregation rules retained the production result. The final reported impact is LOW.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate (with actual score 1) MAYBE VIRT UAF HARDWARE DECREASED_TO_MODERATE_REGULAR_FROM_MODERATE7_BASED_ON_GUESSCVSS_AND_CIANNH DECREASED_TO_LOW_FROM_MODERATE_BASED_ON_ACTIONABLESCORELESSTHAN3 KPANIC_UNSUPPORTED_REMOVED V64_AEGIS_UNSUPPORTED_PROMOTION_BLOCKED - - checked ====================================================================== ACTIONABLESCORE ANALYSIS ====================================================================== ActionableScore=1 PrimitiveClass=CLASS_C RealUAF=NO HostAdminRequired=NO NamespaceScopedPrivilege=NO ImportantCandidate=NO ManualReview=NO AutoDowngradeAllowed=YES RequiresHostUID0=NO AuthorizationDecisionBypass=NO ProtectedResourceImpact=NONE B4PendingReview=NO B4PendingConfirmed=NO 1. ActionableScore * Raw base score: 1. * Conservative score: 1; no floor or cap applied. * Raw paranoid score: 1. * Paranoid score: 1; no additional proof-supported impact. * Final recommended bucket: **Ordinary Moderate**:: 2. Signal breakdown * +1 — Concrete persistent kernel resource leak: `have_run_cpus` remains allocated when a migrated source VM is no longer classified as SEV, causing `sev_vm_destroy()` to return before freeing it. * +1 — Availability plausible: repeated SEV migration-and-destruction sequences can accumulate unreclaimed kernel memory and eventually create memory pressure. * -1 — Reduced/delegated privilege: the supplied evidence requires access to KVM VM file descriptors and control of SEV intra-host migration, rather than ordinary unprivileged access. * No UAF, OOB access, invalid dereference, double release, structured-state corruption, authorization bypass, or arbitrary write is shown. * Reliable crash/strong DoS is not awarded; eventual exhaustion requires sustained repetition and is not shown as immediate or guaranteed. * NEW52/B5-R does not apply: there is no heap OOB write or retry-accumulated index. * NEW53/B3-PENDING does not apply: no shared-backing write exists. * NEW54/B4-PENDING does not apply: no DENY-to-ALLOW authorization decision changes. 3. Reachability analysis The supported attacker is a local VMM or delegated process holding relevant KVM VM file descriptors and able to perform SEV intra-host migration followed by VM destruction. This is not guest-only or network reachable. The guest does not control the required host-side migration and destruction lifecycle operations. No namespace capability path is involved. Host UID 0 and effective host-administrator powers are not required when the VM resources have been delegated, but prior access to the VM and migration control is required. AMD SEV support is a functional prerequisite, though the evidence does not justify a rare-hardware penalty. No race is required. 4. Primitive and severity reading The exact defect is a persistent cpumask allocation leak caused by cleanup being conditional on the VM's current SEV state, despite migration having changed that state. The fix moves `free_cpumask_var()` before the early return. This is CLASS_C resource-management/availability behavior, not a UAF or memory-corruption primitive. The shown consequence is incremental kernel-memory loss; host exhaustion is plausible only after sustained repetition. There is no guest-to-host corruption, protected-state change, or material unknown exploit primitive. Therefore ImportantCandidate is NO and automatic Moderate downgrade remains allowed. 5. One-sentence report phrase SEV intra-host migration can leave `have_run_cpus` permanently allocated when the converted source VM is destroyed, allowing repeated privileged VM lifecycle operations to accumulate kernel memory. 6. Manual review advice NO MANUAL CHECK NEEDED The patch establishes a bounded resource-lifetime cleanup defect without memory corruption, authorization bypass, or an unresolved Important-grade primitive. 7. Call-site confidence Call-site confidence: high ====================================================================== UPSTREAM PATCH SUMMARY ====================================================================== Patch: KVM: SEV: Free have_run_cpus during VM destruction even if VM is no longer SEV Commit: 6aef7cf800098749ff5d660222efaf6e01e98c09 Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=6aef7cf800098749ff5d660222efaf6e01e98c09 Commit description: Unconditionally free SEV's "have run CPUs" cpumask in the VM destroy path, i.e. even for what appear to be non-SEV VMs, as an SEV VM becomes a non-SEV VM if its state is intra-host migrated. Alternatively, the mask could be freed in sev_migrate_from() when "converting" the source VM, but that gets annoying because ideally KVM would nullify the mask to guard against UAF, and nullifying the mask would need be conditioned on CPUMASK_OFFSTACK=y. Freeing the mask during sev_migrate_from() is also not robust against other KVM bugs, though that's kind of a moot point since any such bugs would show up even if sev->active is never set. I.e. KVM must get that side of things correct. But, that's not a great reason to add more code just to make things marginally less robust. Fixes: 6f38f8c ("KVM: SVM: Flush cache only on CPUs running SEV guest") Cc: stable@vger.kernel.org Reported-by: Stefan Teodorescu Signed-off-by: Sean Christopherson Message-ID: <20260923163721.1584779-2-seanjc@google.com> Signed-off-by: Paolo Bonzini Signed-off-by: Greg Kroah-Hartman Changed files: arch/x86/kvm/svm/sev.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=6aef7cf800098749ff5d660222efaf6e01e98c09 ====================================================================== DETAILED REPORT METHODOLOGY ====================================================================== The original Linux kernel CVE announcement for CVE-2026-98472 can be found here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98472 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:L/PR:L/UI:N/S:U/C:N/I:N/A:L The Best / paranoid CVSS vector: AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H The Best / paranoid CVSS score: 5.5 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: unknown Paranoid ActionableScore: 1 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: LOW KPANIC detected for this report: NO Published priority for this report (same as in Subject): LOW 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).