From mboxrd@z Thu Jan 1 00:00:00 1970 From: AL-KERNEL To: kernel-cve@kernelcve.org Subject: [CVE-2026-64229][LOW] x86/mm: Disable broadcast TLB flush when PCID is disabled [ Upstream Date: Fri, 24 Jul 2026 12:49:01 -0400 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-AL-KERNEL-CVE: CVE-2026-64229 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: fed725cace3ab1c4f7f8182e35029a603d953187 List-Id: CVE: CVE-2026-64229 Priority: LOW AL-KERNEL base severity: LOW KPANIC flag: NO Patch: x86/mm: Disable broadcast TLB flush when PCID is disabled [ Upstream Commit: fed725cace3ab1c4f7f8182e35029a603d953187 Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=fed725cace3ab1c4f7f8182e35029a603d953187 Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64229 Analysis date: Fri, 24 Jul 2026 12:49:01 -0400 ActionableScore: 2 ActionableScore lower bound: unknown Actionable bucket: Ordinary Moderate / Low-like Manual review required: NO Summary: On AMD systems booted with `nopcid`, broadcast TLB flushing can issue `INVLPGB` with a non zero PCID while `CR4.PCIDE` is clear, allowing a local user to trigger a kernel #GP and denial of service through multi CPU memory activity. ====================================================================== ABOUT THIS REPORT ====================================================================== The original Linux kernel CVE announcement for CVE-2026-64229 is available here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64229 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-2026-64229 LOW CHECK WITH IMPACT FROM ORIG NN LOW 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-703;CWE-754;CWE-248;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '5.5';DESCR 'Broadcast TLB flushing on AMD systems with INVLPGB can remain enabled when the kernel is booted with nopcid and CR4.PCIDE is not set. Once a process mm becomes active on several CPUs, flush_tlb_mm_range may use broadcast_tlb_flush with a non zero PCID and INVLPGB raises a general protection fault in the host kernel. A local user can plausibly trigger the crash by running multi threaded memory activity that causes TLB flushes, but only on affected AMD CPUs and only when PCID was disabled at boot. For the CVSS the PR:L is selected because the attacker needs local code execution as an unprivileged user, while the insecure nopcid boot configuration is treated as an environmental precondition rather than attacker privilege. The issue is not network reachable. Impact is denial of service via kernel crash, with no evidence of UAF, OOB access, information disclosure, or privilege escalation.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate / Low-like (with actual score 2) SKIP CVE-2026-64229 UNKNOWN SKIP The Fixes patch not applied yet, so unlikely that actual: 4afeb0ed1753ebcad93ee3b45427ce85e9c8ec40 YES NO NO unknown MAYBE NULLPTR HARDWARE DECREASED_TO_MODERATE_REGULAR_FROM_MODERATE7_BASED_ON_GUESSCVSS_AND_CIANNH 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 Triggered signals: * **Local unprivileged trigger: +1** A local unprivileged process can plausibly make an mm active on multiple CPUs and trigger TLB flushes through ordinary memory activity. * **Reliable kernel crash / strong DoS: +1** The commit shows a concrete #GP in `broadcast_tlb_flush()` leading to an Oops or panic path. * **Broad core subsystem context: +1** The bug is in x86 MM / TLB management, a core kernel path. Subtracting signals: * **Legacy / non-default execution mode: -1** The issue requires booting with `nopcid`, which is not the normal/default configuration. Not triggered: * No remote reachability. * No firmware-mediated external influence. * No UAF, OOB write, double-free, refcount takeover, type confusion, or arbitrary write. * No plausible confidentiality or integrity impact. * No privilege escalation primitive. Call-site confidence: **high**. The commit includes the concrete path through `flush_tlb_mm_range()` and `broadcast_tlb_flush()`. ## 3. Reachability analysis The bug is reachable only on AMD systems supporting `INVLPGB` when the kernel is booted with `nopcid`, so `CR4.PCIDE` is not enabled while broadcast TLB invalidation remains available. A local user can plausibly trigger the crash by causing multi-CPU memory activity that reaches the global ASID and broadcast TLB flush path. Namespaces or containers do not materially change the primitive, because the required action is local memory activity rather than privileged configuration. The vulnerable configuration is non-default and hardware-dependent. ## 4. Severity interpretation This behaves like an **ordinary Moderate / Low-like availability bug**, not an Important-class vulnerability. The demonstrated failure mode is a kernel #GP / crash. There is no evidence of memory corruption beyond the fault itself, no stale lifetime object, no attacker-controlled overwrite, no information disclosure, and no privilege escalation path. The realistic impact is local DoS under a specific boot configuration. ## 5. One-sentence report phrase On AMD systems booted with `nopcid`, broadcast TLB flushing can issue `INVLPGB` with a non zero PCID while `CR4.PCIDE` is clear, allowing a local user to trigger a kernel #GP and denial of service through multi CPU memory activity. ## 6. Manual review recommendation **NO MANUAL CHECK NEEDED** This is a configuration-dependent local DoS with a clear crash mechanism and no supported memory-corruption, confidentiality, integrity, network, or privilege-escalation primitive. ====================================================================== UPSTREAM PATCH SUMMARY ====================================================================== Patch: x86/mm: Disable broadcast TLB flush when PCID is disabled [ Upstream Commit: fed725cace3ab1c4f7f8182e35029a603d953187 Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=fed725cace3ab1c4f7f8182e35029a603d953187 Changed files: arch/x86/kernel/cpu/cpuid-deps.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=fed725cace3ab1c4f7f8182e35029a603d953187 ====================================================================== DETAILED REPORT METHODOLOGY ====================================================================== The original Linux kernel CVE announcement for CVE-2026-64229 can be found here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64229 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:H 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: 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).