From mboxrd@z Thu Jan 1 00:00:00 1970 From: AL-KERNEL To: kernel-cve@kernelcve.org Subject: [CVE-2026-93259][MODERATE REGULAR] powerpc/irq: Fix missing r2 clobber in PCREL inline assembly [ Upstream Date: Thu, 24 Sep 2026 21:29:25 -0400 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-AL-KERNEL-CVE: CVE-2026-93259 X-AL-KERNEL-Priority: MODERATE REGULAR X-AL-KERNEL-Severity: MODERATE REGULAR X-AL-KERNEL-Base-Severity: MODERATE X-AL-KERNEL-KPANIC: NO X-AL-KERNEL-ActionableScore: 2 X-AL-KERNEL-ActionableScore-Lower: unknown X-AL-KERNEL-Commit: dcc442a49c0f540193910dacdca7506bcadc7ec5 List-Id: CVE: CVE-2026-93259 Priority: MODERATE REGULAR AL-KERNEL base severity: MODERATE KPANIC flag: NO Patch: powerpc/irq: Fix missing r2 clobber in PCREL inline assembly [ Upstream Commit: dcc442a49c0f540193910dacdca7506bcadc7ec5 Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=dcc442a49c0f540193910dacdca7506bcadc7ec5 Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-93259 Analysis date: Thu, 24 Sep 2026 21:29:25 -0400 ActionableScore: 2 ActionableScore lower bound: unknown 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-2026-93259 is available here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-93259 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 REGULAR 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-2026-93259 MODERATE https://www.kernelcve.org/list/?q=CVE-2026-93259 CHECK WITH IMPACT FROM ORIG NN MODERATE 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:H';CWE-758;*CWE-787;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '5.8';DESCR 'A missing r2 clobber in PowerPC PCREL inline assembly allows the compiler to keep a live value in r2 across calls to __do_irq or __do_softirq even though the called code may overwrite that register. Later kernel code can use the corrupted value to calculate a write address, resulting in a bad area write, an Oops, and failure to boot or continue interrupt processing. The issue requires CONFIG_PPC_KERNEL_PCREL and a compiler register allocation that keeps a live value in r2, as observed with GCC 14, so AC:H reflects the build and runtime conditions. For the CVSS the PR:L value represents a conservative local triggering model in which a user process can generate activity that leads to interrupt or softirq handling, although the underlying fault may also occur without a deliberate attacker. The issue is not directly network reachable. Network traffic may indirectly generate interrupts or softirqs, but the available evidence does not show reliable remote control of the corrupted register or write target. Impact is confirmed as denial of service. Limited confidentiality or integrity impact remains a worst case possibility if the corrupted address resolves to writable kernel memory, but no controlled arbitrary write or privilege escalation path is demonstrated.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate (with actual score 2) SKIP CVE-2026-93259 UNKNOWN SKIP The Fixes patch not applied yet, so unlikely that actual: url YES NO NO unknown MAYBE DANGER HARDWARE LINUS DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN4 - - checked ====================================================================== ACTIONABLESCORE ANALYSIS ====================================================================== ActionableScore=2 PrimitiveClass=CLASS_C RealUAF=NO HostAdminRequired=NO NamespaceScopedPrivilege=NO ImportantCandidate=NO ManualReview=RECOMMENDED AutoDowngradeAllowed=YES 1. ActionableScore * Raw conservative score: 2 * Conservative score: 2 * Raw paranoid score: 2 * Paranoid score: 2 * No floor or cap applied. * Final recommended bucket: **Ordinary Moderate**:: 2. Signal breakdown Positive signals: * +1 Weak or indirect corruption candidate. The missing inline-assembly clobber allows a live compiler-managed value in `r2` to be overwritten and later used in address calculation. This establishes register corruption and an attempted write through an invalid address, but not a controlled or successful kernel overwrite. * +1 Reliable kernel crash or strong DoS. The supplied trace demonstrates a kernel bad-area write fault and Oops during interrupt handling, and the affected build fails to boot. Negative signals: * No negative points applied. `CONFIG_PPC_KERNEL_PCREL` and GCC 14 are prerequisites, but the evidence does not establish that they constitute a rare hardware requirement or sufficiently unusual execution mode for a penalty. * No host-administrator penalty. Interrupt and softirq processing itself does not require an attacker to possess administrative privileges. Material non-awarded signals: * Local unprivileged trigger +1 was not awarded because ordinary users may generate activity that causes interrupts, but reliable attacker control over the relevant interrupt execution and corrupted `r2` value is not established. * Remote reachability +2 was not awarded. Network traffic may indirectly cause IRQ or softirq processing, but this does not establish a reliable direct network trigger. * Strong or constrained overwrite points were not awarded because the trace shows a faulting write attempt rather than a successful overwrite of mapped kernel memory. * Integrity impact was not awarded because no successful unauthorized modification is demonstrated. * Confidentiality impact was not awarded because there is no read-back or disclosure path. * Weak or strong LPE leverage was not awarded because the attacker cannot select the corrupted register value, write target, or payload. * Extra Availability was not awarded because the boot failure and kernel Oops are the same crash consequence. * Controlled reclaim, arbitrary write, callback influence, authorization bypass, and privilege escalation are not demonstrated. 3. Reachability analysis The defect affects PowerPC kernels built with `CONFIG_PPC_KERNEL_PCREL` when compiler register allocation keeps a live value in caller-saved `r2` across the inline assembly call. GCC 14 is shown to produce such code, while older GCC versions happened to avoid the defect. No administrative operation is required to enter IRQ or softirq handling, so host-admin-equivalent privilege is not required. However, the evidence does not establish that an ordinary local attacker can reliably control the exact execution state, the value left in `r2`, or the resulting write address. The kernel may fail naturally during boot or routine interrupt processing without any adversarial action. No namespace capability is involved, and namespace creation does not change reachability. There is no prior privileged runtime setup beyond installing or booting an affected kernel build. No special peripheral is identified, although the issue is architecture and build-configuration specific. This is not a timing race. 4. Primitive and severity interpretation The exact primitive is compiler-visible register-state corruption caused by an incomplete inline-assembly clobber list. A called function may overwrite `r2`, while the compiler incorrectly assumes that a value held there survives. Subsequent code can use the corrupted value in an address calculation and attempt a kernel write. This is not a UAF, lifetime violation, repeated release, or stale structured-object use. The demonstrated result is an invalid write attempt that faults immediately and causes an Oops or boot failure. A successful write to mapped kernel memory is theoretically possible for another register allocation or runtime value, but the supplied evidence does not establish attacker influence over the destination or value. The issue is therefore CLASS_C rather than CLASS_A or CLASS_B. ImportantCandidate is NO because no independently useful corruption, disclosure, authorization bypass, or privilege-escalation primitive is established. AutoDowngradeAllowed is YES because the demonstrated security effect is constrained to crash and availability loss, while stronger consequences remain unsupported. Likely operational severity is Low-like to ordinary Moderate. The practical priority is higher for distributors shipping affected PowerPC PCREL kernels compiled with toolchains that expose the missing clobber. 5. One-sentence report phrase A missing r2 clobber in PowerPC PCREL interrupt assembly can corrupt a compiler-managed address value and cause an invalid kernel write attempt, resulting in an Oops or boot failure without a demonstrated attacker-controlled overwrite. 6. Manual review recommendation MANUAL CHECK RECOMMENDED Review generated code across supported PowerPC compiler versions to confirm whether any affected build can produce a successful write into mapped kernel memory rather than the demonstrated immediate fault. 7. Call-site confidence Call-site confidence: high ====================================================================== UPSTREAM PATCH SUMMARY ====================================================================== Patch: powerpc/irq: Fix missing r2 clobber in PCREL inline assembly [ Upstream Commit: dcc442a49c0f540193910dacdca7506bcadc7ec5 Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=dcc442a49c0f540193910dacdca7506bcadc7ec5 Changed files: arch/powerpc/kernel/irq.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=dcc442a49c0f540193910dacdca7506bcadc7ec5 ====================================================================== DETAILED REPORT METHODOLOGY ====================================================================== The original Linux kernel CVE announcement for CVE-2026-93259 can be found here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-93259 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:H/PR:L/UI:N/S:U/C:L/I:L/A:H The Best / paranoid CVSS score: 5.8 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: 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: MODERATE KPANIC detected for this report: NO Published priority for this report (same as in Subject): MODERATE REGULAR 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).