From mboxrd@z Thu Jan 1 00:00:00 1970 From: AL-KERNEL To: kernel-cve@kernelcve.org Subject: [CVE-2026-46014][LOW] KVM: SVM: Add missing save/restore handling of LBR MSRs Date: Wed, 27 May 2026 16:46:11 -0400 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-AL-KERNEL-CVE: CVE-2026-46014 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: 2 X-AL-KERNEL-ActionableScore-Lower: unknown X-AL-KERNEL-Commit: 2b922a42b531a82d7881add14a7698dcdc5e1f0a List-Id: CVE: CVE-2026-46014 Priority: LOW AL-KERNEL base severity: LOW KPANIC flag: NO Patch: KVM: SVM: Add missing save/restore handling of LBR MSRs Commit: 2b922a42b531a82d7881add14a7698dcdc5e1f0a Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=2b922a42b531a82d7881add14a7698dcdc5e1f0a Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-46014 Analysis date: Wed, 27 May 2026 16:46:11 -0400 ActionableScore: 2 ActionableScore lower bound: unknown Actionable bucket: Ordinary Moderate / Low-like Manual review required: NO Summary: No one-sentence report phrase was found. ====================================================================== ABOUT THIS REPORT ====================================================================== The original Linux kernel CVE announcement for CVE-2026-46014 is available here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-46014 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-2026-46014 LOW CHECK 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:L';CWE-665;*CWE-664;CWE-703;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:L';BEST CVSS score: '4.5';DESCR 'KVM SVM did not enumerate DEBUGCTL and LBR MSRs for save\/restore and did not fully restore LBR state for nested SVM transitions. This can break VM migration or nested state restore by losing or corrupting guest LBR debug state, especially when LBR virtualization is enabled. For the CVSS the PR:L is used because triggering requires access to KVM userspace ioctls or control of VM save\/restore flow, but not full host root in deployments where VM execution is delegated. The issue is not network reachable by itself and does not provide a host memory corruption primitive. Impact is mainly guest state correctness and limited guest availability or integrity, with only limited confidentiality concern for possible guest branch history state confusion.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate / Low-like (with actual score 2) MAYBE DANGER VIRT INIT HARDWARE LINUS DECREASED_TO_MODERATE_REGULAR_FROM_MODERATE7_BASED_ON_GUESSCVSS DECREASED_TO_LOW_FROM_MODERATE_BASED_ON_ACTIONABLESCORELESSTHAN3 - - checked ====================================================================== ACTIONABLESCORE ANALYSIS ====================================================================== ActionableScore=2 1. ActionableScore * Conservative score: 2 * Paranoid score: 2 * Final recommended bucket: **Ordinary Moderate / Low-like**:: 2. Signal breakdown * Local delegated KVM control: +1. Triggering requires access to KVM userspace ioctls or control over VM save/restore or migration state. * Availability or correctness impact: +1. Broken LBR save/restore can corrupt guest debug/branch-record state and break migration or nested restore correctness. * Rare/configuration-dependent condition: -1. Meaningful impact depends on LBR virtualization, SVM or nested SVM state, and VM save/restore flows. * No memory corruption signal. The patch handles MSR enumeration and architectural state migration, not UAF, OOB write, arbitrary write, or host memory lifetime corruption. * No host privilege escalation or network trigger. The issue affects guest state correctness, not a demonstrated guest-to-host escape or host compromise path. 3. Reachability analysis A local actor with permission to manage a KVM VM, perform save/restore, or run nested virtualization can trigger the affected state transitions. In many deployments this may be a non-root user if `/dev/kvm` access is delegated, but it still requires VM control rather than ordinary local code execution. Containers matter only if they are granted KVM device access. The issue is not network reachable by itself. 4. Severity interpretation This behaves like a Low-like or ordinary Moderate KVM state correctness bug. The realistic impact is VM migration failure, nested restore misbehavior, or loss/corruption of guest LBR debug state. There is no evidence of host memory corruption, host confidentiality impact, host integrity impact, or privilege escalation. 5. One-sentence report phrase KVM SVM failed to save and restore DEBUGCTL and LBR MSRs across VM migration or nested SVM restore, causing guest branch-debug state corruption without evidence of host compromise. 6. Manual review recommendation NO MANUAL CHECK NEEDED. This is a guest state save/restore correctness issue with no supported memory corruption, security-boundary bypass, or host privilege-escalation primitive. ====================================================================== UPSTREAM PATCH SUMMARY ====================================================================== Patch: KVM: SVM: Add missing save/restore handling of LBR MSRs Commit: 2b922a42b531a82d7881add14a7698dcdc5e1f0a Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=2b922a42b531a82d7881add14a7698dcdc5e1f0a Commit description: MSR_IA32_DEBUGCTLMSR and LBR MSRs are currently not enumerated by KVM_GET_MSR_INDEX_LIST, and LBR MSRs cannot be set with KVM_SET_MSRS. So save/restore is completely broken. Fix it by adding the MSRs to msrs_to_save_base, and allowing writes to LBR MSRs from userspace only (as they are read-only MSRs) if LBR virtualization is enabled. Additionally, to correctly restore L1's LBRs while L2 is running, make sure the LBRs are copied from the captured VMCB01 save area in svm_copy_vmrun_state(). Note, for VMX, this also fixes a flaw where MSR_IA32_DEBUGCTLMSR isn't reported as an MSR to save/restore. Note #2, over-reporting MSR_IA32_LASTxxx on Intel is ok, as KVM already handles unsupported reads and writes thanks to commit b5e2fec ("KVM: Ignore DEBUGCTL MSRs with no effect") (kvm_do_msr_access() will morph the unsupported userspace write into a nop). Fixes: 24e09cb ("KVM: SVM: enable LBR virtualization") Cc: stable@vger.kernel.org Reported-by: Jim Mattson Signed-off-by: Yosry Ahmed Link: https://patch.msgid.link/20260303003421.2185681-4-yosry@kernel.org [sean: guard with lbrv checks, massage changelog] Signed-off-by: Sean Christopherson Signed-off-by: Greg Kroah-Hartman Changed files: arch/x86/kvm/svm/nested.c arch/x86/kvm/svm/svm.c arch/x86/kvm/x86.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=2b922a42b531a82d7881add14a7698dcdc5e1f0a ====================================================================== DETAILED REPORT METHODOLOGY ====================================================================== The original Linux kernel CVE announcement for CVE-2026-46014 can be found here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-46014 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:L The Best / paranoid CVSS vector: AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:L/A:L The Best / paranoid CVSS score: 4.5 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: 2 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).