From mboxrd@z Thu Jan 1 00:00:00 1970 From: AL-KERNEL To: kernel-cve@kernelcve.org Subject: [CVE-2026-89961][MODERATE 7.0] powerpc/mm: fix wrong addr_pfn tracking in compound vmemmap population Date: Wed, 16 Sep 2026 13:20:42 -0400 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-AL-KERNEL-CVE: CVE-2026-89961 X-AL-KERNEL-Priority: MODERATE 7.0 X-AL-KERNEL-Severity: MODERATE 7.0 X-AL-KERNEL-Base-Severity: MODERATE X-AL-KERNEL-KPANIC: NO X-AL-KERNEL-ActionableScore: 5 X-AL-KERNEL-ActionableScore-Lower: 3 X-AL-KERNEL-Commit: b96be860673f9fbbf12cdadb0b25fc4d6d4d207f List-Id: CVE: CVE-2026-89961 Priority: MODERATE 7.0 AL-KERNEL base severity: MODERATE KPANIC flag: NO Patch: powerpc/mm: fix wrong addr_pfn tracking in compound vmemmap population Commit: b96be860673f9fbbf12cdadb0b25fc4d6d4d207f Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=b96be860673f9fbbf12cdadb0b25fc4d6d4d207f Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89961 Analysis date: Wed, 16 Sep 2026 13:20:42 -0400 ActionableScore: 5 ActionableScore lower bound: 3 Actionable bucket: Actionable Moderate / Strong Important candidate requiring manual review Manual review required: YES Summary: No one-sentence report phrase was found. ====================================================================== ABOUT THIS REPORT ====================================================================== The original Linux kernel CVE announcement for CVE-2026-89961 is available here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89961 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 7.0 Manual review required: YES A detailed explanation of the methodology and priority rules is included at the end of this message. ====================================================================== AL-KERNEL CLASSIFICATION RESULT ====================================================================== CVE-2026-89961 MODERATE https://www.kernelcve.org/list/?q=CVE-2026-89961 CHECK WITH IMPACT FROM ORIG NN LOW Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H';CWE-682;CWE-665;CWE-119;Other CVSS 'AV:L/AC:H/PR:H/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '7';DESCR 'Wrong addr_pfn tracking in powerpc compound vmemmap population can make the code compute pfn_offset from the wrong PFN and choose the wrong head or tail struct page mapping. This affects low level memory metadata for compound pages on powerpc Book3S64 radix systems with vmemmap optimization. The realistic trigger is local and configuration dependent, usually through privileged memory hotplug or device memory setup rather than a normal unprivileged syscall. For the CVSS the PR:L in the paranoid score reflects deployments where limited host management roles or service accounts can trigger memory add or device memory setup without full root equivalence. The issue is not network reachable. Impact is at least denial of service via kernel crash, and in the worst defensible case may affect confidentiality and integrity because incorrect struct page metadata mapping is a memory corruption candidate.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate / Strong Important candidate requiring manual review (with actual score 4) YES READ OOB SIMPLEFIX HARDWARE MEMORY DECREASED_TO_MODERATEREG_BASED_ON_FALSEPOSCHECKOFKP YES NO checked ====================================================================== ACTIONABLESCORE ANALYSIS ====================================================================== ActionableScore=5 ActionableScoreLower=3 PrimitiveClass=CLASS_B RealUAF=NO HostAdminRequired=UNKNOWN NamespaceScopedPrivilege=NO ImportantCandidate=YES ManualReview=REQUIRED AutoDowngradeAllowed=NO 1. ActionableScore * Raw conservative score: 3 * Conservative score: 3. No floor or cap applied. * Raw paranoid score: 5 * Paranoid score: 5. No floor or cap applied. * Final recommended bucket: **Actionable Moderate / Strong Important candidate requiring manual review**:: 2. Signal breakdown Conservative signals: * +2 CLASS_B active memory metadata corruption candidate. The bug can compute pfn_offset from the wrong PFN and choose the wrong head or tail struct page mapping during compound vmemmap population. * +1 Memory layout invariant restoration. The patch fixes inconsistent tracking between vmemmap address progression and data PFN progression. * +1 Reliable kernel crash / strong DoS plausible. Incorrect vmemmap metadata for compound pages can plausibly lead to kernel faults or memory-management failure when the affected metadata is later used. * -1 Specialized architecture and configuration. The affected path is powerpc Book3S64 radix vmemmap optimization, not a generic syscall path. Paranoid additional signal: * +1 Weak LPE concern. The wrong head/tail struct page mapping is a meaningful invalid structured-object interpretation in low-level page metadata, so limited integrity/confidentiality concern is defensible for manual triage, although not proven. Non-awarded signals: * RealUAF not awarded. The patch does not establish a freed object being used after lifetime end. * Concrete repeated release/refcount not awarded. No first put/free followed by a second lifetime mutation on the same dangling reference is shown. * Strong exploitation leverage not awarded. Controlled reclaim, arbitrary write, callback control, refcount takeover, or demonstrated LPE is not established. * Remote reachability not awarded. This is not packet or network triggered. * Local unprivileged trigger not awarded. Ordinary user reachability is not established. * C/I as proven impact not awarded. The paranoid score reflects unresolved memory metadata corruption concern, not demonstrated disclosure or unauthorized write. 3. Reachability analysis The vulnerable function is a low-level meminit path for powerpc Book3S64 radix vmemmap optimization. The realistic trigger appears tied to memory hotplug, device memory setup, or similar kernel memory-management initialization paths. Those operations are normally privileged, but the supplied input does not fully prove that host-admin-equivalent privilege is required for every possible affected deployment, so HostAdminRequired is UNKNOWN rather than YES. No evidence shows that the complete trigger chain is namespace-scoped. NamespaceScopedPrivilege is NO. No network trigger is present. No ordinary syscall path for an unprivileged local user is established. No race timing is required by the patch itself. The main prerequisite is affected architecture and vmemmap optimization support. 4. Primitive and severity interpretation The primitive is not a UAF. It is an active low-level memory metadata consistency violation: vmemmap_populate_compound_pages() may select the wrong head or tail struct page mapping because addr_pfn does not track the current vmemmap address correctly. This is CLASS_B because it affects active struct page metadata and compound-page representation, but the patch does not establish a CLASS_A primitive such as controlled overwrite, controlled reclaim, arbitrary read/write, refcount takeover, or demonstrated privilege escalation. Demonstrated consequence from the patch is incorrect vmemmap population logic. Practical consequence is likely crash or memory-management malfunction on affected systems. Speculative consequence is broader page metadata corruption that could affect integrity or confidentiality, but this remains unresolved and requires manual review. ImportantCandidate is YES because wrong struct page metadata mapping is a meaningful kernel memory-management corruption candidate. AutoDowngradeAllowed is NO because automatically closing it as ordinary Moderate could miss unresolved exploitation leverage in core memory metadata. 5. One-sentence report phrase Wrong addr_pfn tracking in powerpc compound vmemmap population can cause incorrect head or tail struct page metadata mappings, creating a kernel memory metadata corruption candidate with likely DoS impact and unresolved stronger security implications. 6. Manual review recommendation MANUAL CHECK REQUIRED Reason: the patch affects low-level struct page metadata mapping for compound pages, and the worst defensible interpretation is broader memory metadata corruption even though UAF, arbitrary write, and LPE are not demonstrated. 7. Call-site confidence Call-site confidence: medium ====================================================================== UPSTREAM PATCH SUMMARY ====================================================================== Patch: powerpc/mm: fix wrong addr_pfn tracking in compound vmemmap population Commit: b96be860673f9fbbf12cdadb0b25fc4d6d4d207f Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=b96be860673f9fbbf12cdadb0b25fc4d6d4d207f Commit description: vmemmap_populate_compound_pages() uses addr_pfn to determine the PFN offset within a compound page and to decide whether the current vmemmap slot should be populated as a head page mapping or should reuse a tail page mapping. However, addr_pfn is advanced manually in parallel with addr. The loop itself progresses in vmemmap address space, so each PAGE_SIZE step in addr covers PAGE_SIZE / sizeof(struct page) struct page slots. Since addr_pfn is compared against nr_pages in data-PFN units, it should advance by the same number of PFNs. The existing manual increments do not match that and therefore do not reliably track the PFN corresponding to the current addr. As a result, pfn_offset can be computed from the wrong PFN and the code can make the head/tail decision for the wrong compound-page position. Fix this by deriving addr_pfn directly from the current vmemmap address instead of carrying it as loop state. Link: https://lore.kernel.org/20260612035903.2468601-4-songmuchun@bytedance.com Fixes: f2b79c0 ("powerpc/book3s64/radix: add support for vmemmap optimization for radix") Signed-off-by: Muchun Song Acked-by: Oscar Salvador Reviewed-by: Ritesh Harjani (IBM) Cc: "Aneesh Kumar K.V" Cc: David Hildenbrand Cc: Frank van der Linden Cc: Liam R. Howlett Cc: Lorenzo Stoakes Cc: Madhavan Srinivasan Cc: Michael Ellerman Cc: Mike Rapoport (Microsoft) Cc: Nicholas Piggin Cc: Oscar Salvador (SUSE) Cc: Usama Arif Cc: Vlastimil Babka Cc: Signed-off-by: Andrew Morton Signed-off-by: Greg Kroah-Hartman Changed files: arch/powerpc/mm/book3s64/radix_pgtable.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=b96be860673f9fbbf12cdadb0b25fc4d6d4d207f ====================================================================== DETAILED REPORT METHODOLOGY ====================================================================== The original Linux kernel CVE announcement for CVE-2026-89961 can be found here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89961 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:H The Best / paranoid CVSS vector: AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H The Best / paranoid CVSS score: 7 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: 3 Paranoid ActionableScore: 5 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 7.0 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).