From mboxrd@z Thu Jan 1 00:00:00 1970 From: AL-KERNEL To: kernel-cve@kernelcve.org Subject: [CVE-2025-40181][LOW] x86/kvm: Force legacy PCI hole to UC when overriding MTRRs for TDX/SNP [ Upstream Date: Wed, 09 Sep 2026 02:35:03 -0400 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-AL-KERNEL-CVE: CVE-2025-40181 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: 0 X-AL-KERNEL-Commit: 34ff466f74d0fe1db8956f9c245e2bb2c67f67bf List-Id: CVE: CVE-2025-40181 Priority: LOW AL-KERNEL base severity: LOW KPANIC flag: NO Patch: x86/kvm: Force legacy PCI hole to UC when overriding MTRRs for TDX/SNP [ Upstream Commit: 34ff466f74d0fe1db8956f9c245e2bb2c67f67bf Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=34ff466f74d0fe1db8956f9c245e2bb2c67f67bf Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2025-40181 Analysis date: Wed, 09 Sep 2026 02:35:03 -0400 ActionableScore: 1 ActionableScore lower bound: 0 Actionable bucket: Ordinary Moderate Manual review required: NO Summary: No one-sentence report phrase was found. ====================================================================== ABOUT THIS REPORT ====================================================================== The original Linux kernel CVE announcement for CVE-2025-40181 is available here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2025-40181 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-2025-40181 LOW https://www.kernelcve.org/list/?q=CVE-2025-40181 CHECK WITH IMPACT FROM ORIG NN MODERATE Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:L/PR:H/UI:N/S:U/C:N/I:L/A:L';CWE-693;CWE-665;CWE-754;Other CVSS 'AV:L/AC:H/PR:H/UI:N/S:U/C:N/I:N/A:L';BEST CVSS score: '3.4';DESCR 'x86/KVM guests using TDX or SNP can get inconsistent cache type tracking for the legacy PCI hole because Linux forces default WB MTRRs while ACPI SystemMemory mappings may be created as WB before device drivers request UC or WC mappings. This can make TPM TIS or similar legacy MMIO device probe fail with an ioremap memtype conflict, leaving the device unavailable inside the guest. For the CVSS the PR:H is used because reliable triggering normally requires control over the VM platform, hypervisor supplied ACPI tables, or confidential guest launch environment, not an unprivileged local interface inside the guest. The issue is not network reachable. Impact is mainly availability loss of guest device functionality and possibly a low integrity impact if security features depending on TPM availability are not usable.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate (with actual score 1) MAYBE OOB VIRT INIT HARDWARE DECREASED_TO_MODERATE_REGULAR_FROM_MODERATE7_BASED_ON_GUESSCVSS DECREASED_TO_LOW_FROM_MODERATE_BASED_ON_ACTIONABLESCORELESSTHAN3 - - checked ====================================================================== ACTIONABLESCORE ANALYSIS ====================================================================== ActionableScore=1 ActionableScoreLower=0 PrimitiveClass=NONE RealUAF=NO HostAdminRequired=YES NamespaceScopedPrivilege=NO ImportantCandidate=NO ManualReview=NO AutoDowngradeAllowed=YES 1. ActionableScore * Raw conservative score: 0 * Conservative score: 0 * Raw paranoid score: 1 * Paranoid score: 1 * Final recommended bucket: **Ordinary Moderate**:: No floor or cap changed the score. 2. Signal breakdown Conservative positive signals: * +0. No memory corruption, UAF, OOB access, repeated release, refcount misuse, authorization bypass, or guest-to-host corruption primitive is established. * +0. The demonstrated symptom is an ioremap memtype conflict and device probe failure, not a kernel crash or host-wide DoS. Conservative negative signals: * No numeric privilege penalty was needed because the conservative score already has no attacker-useful primitive to reduce. The supplied context nevertheless supports HostAdminRequired=YES for deliberate triggering because reliable control normally requires VM platform, hypervisor ACPI, or confidential guest launch control. Paranoid positive signals: * +1. Low operational security impact is plausible because TPM TIS or similar legacy MMIO device functionality can be unavailable inside a TDX/SNP guest, which may affect guest attestation or security workflows. Non-awarded signals: * Controlled reclaim not demonstrated. * Arbitrary write not demonstrated. * Real UAF not demonstrated. * Repeated release/refcount mutation not demonstrated. * Authorization bypass not demonstrated. * Guest-to-host exploitation primitive not demonstrated. * Remote reachability not established. * Reliable kernel crash not awarded. The trace shows WARN and device probe failure, not a panic. * Extra Availability not awarded because the effect is device/functionality availability, not a supported host-wide failure. * C/I corruption impact not awarded. The paranoid +1 reflects operational integrity risk from unavailable TPM-backed workflows, not kernel memory integrity corruption. Repeated-release/refcount checklist: * First release can end lifetime: no evidence. * Exact same reference survives: no evidence. * Second lifetime/refcount mutation: no evidence. * Concrete repeated release/refcount +1 awarded: no. * Paranoid repeated-refcount leverage +1 awarded: no. * FLOOR 5 applied: no. 3. Reachability analysis The affected path runs during early x86 KVM guest platform initialization for SEV-SNP or TDX guests when Linux overrides virtual MTRR behavior. The problematic condition depends on ACPI SystemMemory mappings for legacy MMIO devices, such as TPM TIS or HPET, being established as WB before the dedicated device driver requests UC or WC mappings. A normal local user inside the guest is not shown to control the ACPI tables, the confidential guest launch mode, the virtual MTRR override policy, or the legacy PCI hole layout. The realistic actor able to deliberately shape this condition is the VM platform provider, VMM, hypervisor administrator, or equivalent launch environment controller. Therefore HostAdminRequired=YES for an adversarial trigger model. This is not namespace-scoped. No network namespace, user namespace, CAP_NET_ADMIN path, or attacker-created local namespace operation is involved. No direct network trigger is established. No special physical hardware is required beyond running as a TDX/SNP KVM guest with relevant legacy MMIO device exposure, but the attacker-relevant setup is platform controlled rather than ordinary-user controlled. There is no race or timing issue. 4. Primitive and severity interpretation The exact primitive is an inconsistent guest-side cache type tracking state for the legacy PCI hole under forced WB MTRRs in confidential KVM guests. ACPI may create WB mappings for SystemMemory regions, and later TPM or other device drivers may fail to create UC/WC mappings because the kernel memtype tracker sees an incompatible existing mapping. This is a logic/configuration correctness issue, not a memory-safety primitive. It is not active structured stale storage, not fixed stale storage, and not a cleanup UAF. No concrete repeated release/refcount operation exists. PrimitiveClass=NONE because the patch establishes no kernel corruption, lifetime violation, authorization bypass, shared-page ownership violation, or semantic reinterpretation that creates an attacker-useful security primitive. The demonstrated consequence is device unavailability inside the guest, especially TPM probe failure. A speculative consequence is degraded security functionality if the deployment relies on TPM availability for attestation or policy, but no privilege escalation, information disclosure, or guest-to-host boundary compromise is supported. ImportantCandidate=NO because there is no Important-grade primitive and no unresolved kernel corruption leverage. AutoDowngradeAllowed=YES because automatic downgrade would not discard a concrete corruption or authorization primitive. Likely operational severity is Low-like to ordinary Moderate, mainly a correctness and device availability issue in confidential guest environments. 5. One-sentence report phrase TDX or SNP KVM guests may fail to initialize TPM TIS or similar legacy MMIO devices because ACPI WB mappings can conflict with later UC or WC driver mappings, causing guest device availability loss rather than memory corruption or privilege escalation. 6. Manual review recommendation NO MANUAL CHECK NEEDED The patch does not establish memory corruption, UAF, authorization bypass, guest-to-host compromise, or a below-host-admin attacker path. Review may be product-priority driven only if TPM availability inside TDX/SNP guests is security-critical for the deployment. 7. Call-site confidence Call-site confidence: high ====================================================================== UPSTREAM PATCH SUMMARY ====================================================================== Patch: x86/kvm: Force legacy PCI hole to UC when overriding MTRRs for TDX/SNP [ Upstream Commit: 34ff466f74d0fe1db8956f9c245e2bb2c67f67bf Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=34ff466f74d0fe1db8956f9c245e2bb2c67f67bf Changed files: arch/x86/mm/pat/memtype.c arch/x86/kernel/kvm.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=34ff466f74d0fe1db8956f9c245e2bb2c67f67bf ====================================================================== DETAILED REPORT METHODOLOGY ====================================================================== The original Linux kernel CVE announcement for CVE-2025-40181 can be found here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2025-40181 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:H/UI:N/S:U/C:N/I:N/A:L The Best / paranoid CVSS vector: AV:L/AC:L/PR:H/UI:N/S:U/C:N/I:L/A:L The Best / paranoid CVSS score: 3.4 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: 0 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).