From mboxrd@z Thu Jan 1 00:00:00 1970 From: AL-KERNEL To: kernel-cve@kernelcve.org Subject: [CVE-2026-98505][LOW] mm/damon/vaddr: avoid hw-driven pte updates during damon_hugetlb_mkold() [ Upstream Date: Sat, 24 Oct 2026 10:46:31 -0400 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-AL-KERNEL-CVE: CVE-2026-98505 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: 0 X-AL-KERNEL-ActionableScore-Lower: unknown X-AL-KERNEL-Commit: 00457981327c80bcc56e07d4714fe189337a19fa List-Id: CVE: CVE-2026-98505 Priority: LOW AL-KERNEL base severity: LOW KPANIC flag: NO Patch: mm/damon/vaddr: avoid hw-driven pte updates during damon_hugetlb_mkold() [ Upstream Commit: 00457981327c80bcc56e07d4714fe189337a19fa Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=00457981327c80bcc56e07d4714fe189337a19fa Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98505 Analysis date: Sat, 24 Oct 2026 10:46:31 -0400 ActionableScore: 0 ActionableScore lower bound: unknown Actionable bucket: Ordinary Moderate Manual review required: NO Summary: A narrow DAMON/hugetlb PTE race can lose a hardware dirty-bit update, but no memory-corruption, authorization, crash, or cross-boundary primitive is demonstrated. ====================================================================== ABOUT THIS REPORT ====================================================================== The original Linux kernel CVE announcement for CVE-2026-98505 is available here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98505 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-2026-98505 LOW https://www.kernelcve.org/list/?q=CVE-2026-98505 CHECK WITH IMPACT FROM ORIG NN MODERATE | AEGIS IMPACT MODERATE AEGIS_AS=0 LEGACY=LOW RESULT=DIFF (final Legacy and Aegis differ; FINAL: LOW, Aegis: 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:N/I:L/A:L';CWE-362;CWE-367;CWE-662;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:L/A:N';BEST CVSS score: '3.6';DESCR 'A race in damon_hugetlb_mkold can lose a hardware updated dirty bit because the function reads a huge PTE into a local value and later writes that value back after clearing the accessed bit. Triggering requires DAMON monitoring of a hugetlb mapping and a concurrent local write during the narrow PTE update window, so AC:H is appropriate and the issue is not network reachable. For the CVSS the PR:L value reflects that a local process and access to the affected mapping are required for attacker controlled writes, while DAMON monitoring normally must already be enabled by an administrator. The demonstrated primitive is a lost PTE metadata update rather than UAF, OOB access, or arbitrary memory corruption. Integrity impact is low and no direct confidentiality loss, privilege escalation, or reliable host wide denial of service is established. Automated impact decision path. The original SimpleNet classifier selected MODERATE_KPANIC. The primary LLM estimated paranoid CVSS 3.6 and the production ActionableScore returned 0 with recommendation Ordinary Moderate. The production rules then evaluated CVSS thresholds and ActionableScore thresholds. Recorded rule transitions were CVSS and initial triage stage MODERATE_KPANIC to MODERATE because the CVSS score, vector or bug class threshold rule was applied. ActionableScore thresholds stage MODERATE to LOW because the ActionableScore threshold rule was applied. final reconciliation stage LOW to LOW because KP specialist did not establish a qualifying panic and the cross model evidence reconciliation rule was applied. The legacy KP specialist has no review artifact for this run. The legacy FD or DH downgrade specialist has no review artifact for this run. Exact triggered rule markers were DECREASED_TO_MODERATE_REGULAR_FROM_MODERATE7_BASED_ON_GUESSCVSS and DECREASED_TO_LOW_FROM_MODERATE_BASED_ON_ACTIONABLESCORELESSTHAN3 and KPANIC_UNSUPPORTED_REMOVED and V64_AEGIS_UNSUPPORTED_PROMOTION_BLOCKED. The independent weaker Aegis shadow evaluated CVSS 2.5 and ActionableScore 0 with primitive class CLASS_C and manual review REQUIRED. Its independently reconciled impact was MODERATE. The models disagreed but the aggregation rules retained the production result. The final reported impact is LOW.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate (with actual score 0) MAYBE INIT SIMPLEFIX HARDWARE LINUS MEMORY DECREASED_TO_MODERATE_REGULAR_FROM_MODERATE7_BASED_ON_GUESSCVSS DECREASED_TO_LOW_FROM_MODERATE_BASED_ON_ACTIONABLESCORELESSTHAN3 KPANIC_UNSUPPORTED_REMOVED V64_AEGIS_UNSUPPORTED_PROMOTION_BLOCKED - - checked ====================================================================== ACTIONABLESCORE ANALYSIS ====================================================================== ActionableScore=0 PrimitiveClass=CLASS_C RealUAF=NO HostAdminRequired=UNKNOWN NamespaceScopedPrivilege=UNKNOWN ImportantCandidate=NO ManualReview=NO AutoDowngradeAllowed=YES RequiresHostUID0=UNKNOWN AuthorizationDecisionBypass=NO ProtectedResourceImpact=NONE B4PendingReview=NO B4PendingConfirmed=NO 1. ActionableScore * Raw base score: 0. * Conservative score: 0. * Raw paranoid score: 0. * Paranoid score: 0. * Final recommended bucket: **Ordinary Moderate**:: 2. Signal breakdown * +1 concrete active-metadata inconsistency: the stale read-modify-write can overwrite a hardware-updated huge-PTE dirty bit. * -1 hard timing requirement: triggering requires a concurrent hardware PTE update within the narrow interval between `huge_ptep_get()` and `set_huge_pte_at()`. * No OOB write, UAF, arbitrary write, stale object, authorization bypass, disclosure, or reliable crash is shown. * No Integrity point: loss of a hugetlb dirty bit is real metadata damage, but unauthorized modification of another principal’s protected state or persistent storage is not established. * No Important-preserving active-state signal: the patch does not show bypassed mapping retirement, semantic-domain transition, stale reverse mapping, or a specific guest/namespace-to-host boundary. * B5-R and B3-PENDING do not apply: there is neither retry-accumulated heap overwrite nor shared-backing payload write. 3. Reachability analysis A local process can generate hardware dirty-bit updates by writing an affected hugetlb mapping, but DAMON monitoring generally requires separate administrator setup. The evidence does not establish whether one below-host-admin actor can perform the complete setup and trigger, so host-admin and namespace privilege remain unknown. No network path, special hardware requirement, or repeatable attacker-controlled race mechanism is shown. 4. Primitive and severity reading The primitive is a race-induced lost update to active huge-PTE metadata. It is passive state corruption, classified CLASS_C, rather than kernel-memory corruption or a lifetime violation. The fix atomically clears and retrieves the PTE so concurrent writers fault and serialize under the page-table lock. The shown consequence is loss of a dirty-bit update; hugetlbfs is memory-backed and hugetlb pages are not reclaimable, limiting demonstrated downstream impact. Stronger data loss, panic, privilege escalation, or cross-boundary effects remain unsupported. ImportantCandidate=NO because no material exploit or trust-boundary primitive is shown. AutoDowngradeAllowed=YES because the effect is constrained metadata inconsistency with no unresolved concrete corruption chain. 5. One-sentence report phrase A narrow DAMON/hugetlb PTE race can lose a hardware dirty-bit update, but no memory-corruption, authorization, crash, or cross-boundary primitive is demonstrated. 6. Manual review advice NO MANUAL CHECK NEEDED The patch supports a constrained metadata race with no Important-preserving primitive. 7. Call-site confidence Call-site confidence: high ====================================================================== UPSTREAM PATCH SUMMARY ====================================================================== Patch: mm/damon/vaddr: avoid hw-driven pte updates during damon_hugetlb_mkold() [ Upstream Commit: 00457981327c80bcc56e07d4714fe189337a19fa Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=00457981327c80bcc56e07d4714fe189337a19fa Changed files: mm/damon/vaddr.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=00457981327c80bcc56e07d4714fe189337a19fa ====================================================================== DETAILED REPORT METHODOLOGY ====================================================================== The original Linux kernel CVE announcement for CVE-2026-98505 can be found here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98505 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:L/A:N The Best / paranoid CVSS vector: AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:L/A:L The Best / paranoid CVSS score: 3.6 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: 0 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).