From mboxrd@z Thu Jan 1 00:00:00 1970 From: AL-KERNEL To: kernel-cve@kernelcve.org Subject: [CVE-2026-89919][MODERATE 7.0] KVM: s390: keyop: use mmu_lock to read gmap->asce Date: Wed, 16 Sep 2026 15:12:30 -0400 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-AL-KERNEL-CVE: CVE-2026-89919 X-AL-KERNEL-Priority: MODERATE 7.0 X-AL-KERNEL-Severity: MODERATE 7.0 X-AL-KERNEL-Base-Severity: MODERATE X-AL-KERNEL-KPANIC: YES X-AL-KERNEL-ActionableScore: 6 X-AL-KERNEL-ActionableScore-Lower: 5 X-AL-KERNEL-Commit: ae452b990e0544425f77045351c56e77158858e7 List-Id: CVE: CVE-2026-89919 Priority: MODERATE 7.0 AL-KERNEL base severity: MODERATE KPANIC flag: YES Patch: KVM: s390: keyop: use mmu_lock to read gmap->asce Commit: ae452b990e0544425f77045351c56e77158858e7 Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=ae452b990e0544425f77045351c56e77158858e7 Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89919 Analysis date: Wed, 16 Sep 2026 15:12:30 -0400 ActionableScore: 6 ActionableScore lower bound: 5 Actionable bucket: Actionable Moderate / Strong Important candidate requiring manual review Manual review required: YES Summary: KVM s390 keyop can race with VM memory limit updates and use a stale gmap ASCE for host-side memory walking, creating a local VMM-triggerable host memory corruption risk that requires manual review. ====================================================================== ABOUT THIS REPORT ====================================================================== The original Linux kernel CVE announcement for CVE-2026-89919 is available here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89919 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-2026-89919 MODERATE https://www.kernelcve.org/list/?q=CVE-2026-89919 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:H/I:H/A:H';CWE-362;CWE-667;*CWE-787;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:L/A:H';BEST CVSS score: '7';DESCR 'KVM s390 keyop can read gmap asce outside the mmu_lock read side while a concurrent KVM_S390_VM_MEM_LIMIT_SIZE operation updates the same value under the write side of the lock. This race can make KVM_S390_KEYOP walk memory using a stale address space control value and the upstream description states that this can result in memory corruption. For the CVSS the PR:L is selected because reliable triggering requires local access to KVM ioctls from a user or service that can run or control a VM, but it does not require full host root in many deployments. The issue is not directly network reachable and applies to s390 KVM hosts where these ioctls are available. Impact is at least a local denial of service via memory corruption and in worst case may allow confidentiality or integrity impact or privilege escalation, so it should be reviewed manually.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate / Strong Important candidate requiring manual review (with actual score 6) SKIP CVE-2026-89919 UNKNOWN SKIP The Fixes patch not applied yet, so unlikely that actual: url YES NO NO unknown MAYBE DANGER VIRT SIMPLEFIX HARDWARE LINUS KPANIC INCREASED_TO_HIGH_BASED_ON_GUESSCVSS DECREASED_TO_MODERATE7_BASED_ON_FALSEPOSCHECKOFDH - - checked ====================================================================== ACTIONABLESCORE ANALYSIS ====================================================================== ActionableScore=6 ActionableScoreLower=5 PrimitiveClass=CLASS_B RealUAF=NO HostAdminRequired=NO NamespaceScopedPrivilege=NO ImportantCandidate=YES ManualReview=REQUIRED AutoDowngradeAllowed=NO ## 1. ActionableScore * Raw conservative score: 5 * Conservative score: 5 * Raw paranoid score: 6 * Paranoid score: 6 * Final recommended bucket: **Actionable Moderate / Strong Important candidate requiring manual review**:: No floor or cap was applied. ## 2. Signal breakdown Conservative signals: * +2: Patch-established active kernel memory corruption primitive. `kvm_s390_keyop()` could use a stale `gmap->asce` value for address-space walking while `gmap_set_limit()` updates it under `mmu_lock`, and the commit explicitly states this can result in memory corruption. * +1: Active translation synchronization violation. The normal invariant is that `gmap->asce` is read under the `mmu_lock` read side, while writers update it under the write side. * +1: Host-wide DoS or serious host instability is realistic because the corruption occurs in host KVM memory-translation or storage-key handling. * +1: The same local VMM or `/dev/kvm` process can plausibly drive both `KVM_S390_KEYOP` and `KVM_S390_VM_MEM_LIMIT_SIZE`, making the vulnerable concurrent state transition meaningfully triggerable below full host-admin in many KVM deployments. Paranoid additional signal: * +1: Unresolved exploitation leverage in active KVM translation state. The stale ASCE is not merely passive metadata, because it is consumed for a memory walk in a host KVM path. This does not prove arbitrary read/write or guest-to-host escape, but it is enough to prevent automatic downgrade. Non-awarded signals: * RealUAF not awarded: no freed object or post-lifetime object use is directly established. * CLASS_A not awarded: no controlled reclaim, arbitrary write, directed host-memory write, callback control, or demonstrated LPE is shown. * Remote reachability not awarded: this is not directly network-triggerable. * Guest-only trigger not awarded: the supplied evidence shows KVM ioctls, not a pure malicious guest path. * KVM strong guest-to-host leverage +2 not awarded: the patch establishes host KVM memory corruption risk, but not a concrete guest-controlled host read/write or escape primitive. * Race penalty not applied: concurrency is required, but the two relevant ioctls can plausibly be driven repeatedly by the local VMM process. The evidence does not prove a narrow one-shot timing window. * Hardware rarity penalty not applied: the issue is s390-specific, but for affected s390 KVM hosts the feature is intrinsic to the platform rather than an exotic optional peripheral. * Extra Availability not awarded: host instability is already counted once. * Confidentiality and Integrity impact are not separately scored as proven consequences because the patch does not establish a concrete disclosure path or controlled integrity modification target. ## 3. Reachability analysis The evaluated attacker is a local host userspace VMM or management process with access to the relevant KVM VM file descriptor and s390 KVM ioctls. The two operations named in the commit are `KVM_S390_KEYOP` and `KVM_S390_VM_MEM_LIMIT_SIZE`. Host administrator privilege is not positively required by the supplied evidence. KVM device access is often delegated to non-root VMM users or service accounts, so `HostAdminRequired=NO` is used for the practical KVM attacker model. This is not ordinary network reachability and not namespace-scoped privilege. A malicious guest alone is not established as sufficient, because the supplied evidence does not show that guest code can directly issue `KVM_S390_VM_MEM_LIMIT_SIZE` or `KVM_S390_KEYOP`. If guest behavior can induce the VMM to perform one of these operations, that would be a compound guest plus VMM trigger, but that chain is not supplied here. Prior setup is an s390 KVM VM with the relevant ioctls available. The race is between local control-plane operations, not packet traffic. The race is not treated as a hard timing penalty because the same VMM-side actor can plausibly repeat the operations. ## 4. Primitive and severity interpretation The primitive is a race-protected-state violation in KVM s390 address translation state. `gmap->asce` is an active address-space control value used for walking guest mappings or storage-key related state. Reading it outside `mmu_lock` allows `keyop` to operate with a stale ASCE while another ioctl updates the memory limit under the write side of the same lock. This is active structured translation state, not fixed stale storage. It is not a demonstrated UAF. It is also not merely a warning or passive bookkeeping bug, because the stale value is consumed in a host KVM memory-walk path and the commit explicitly says memory corruption can result. PrimitiveClass is `CLASS_B`: a real kernel corruption primitive exists and exploitation-leverage analysis is required, but no CLASS_A primitive such as arbitrary write, controlled replacement, demonstrated LPE, or concrete guest-to-host escape is established. ImportantCandidate is `YES` because host KVM memory corruption in active translation state is too strong to auto-close as ordinary Moderate without manual analysis. AutoDowngradeAllowed is `NO` because automatic downgrade would discard a concrete unresolved kernel-corruption primitive. Likely operational severity is Actionable Moderate at minimum, with Strong Important candidacy depending on whether further review can establish attacker-controlled corruption target, guest-only reachability, or a stronger host memory access primitive. ## 5. One-sentence report phrase KVM s390 keyop can race with VM memory limit updates and use a stale gmap ASCE for host-side memory walking, creating a local VMM-triggerable host memory corruption risk that requires manual review. ## 6. Manual review recommendation MANUAL CHECK REQUIRED Reason: the patch explicitly establishes memory corruption in active KVM translation state, and the unresolved question is whether the stale ASCE walk can be shaped into a stronger host corruption or privilege-impact primitive. ## 7. Call-site confidence Call-site confidence: medium ====================================================================== UPSTREAM PATCH SUMMARY ====================================================================== Patch: KVM: s390: keyop: use mmu_lock to read gmap->asce Commit: ae452b990e0544425f77045351c56e77158858e7 Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=ae452b990e0544425f77045351c56e77158858e7 Commit description: Every other dat_* consumer in this file (kvm_s390_get_skeys, set_skeys, get_cmma_bits, set_cmma_bits, MEM_CLR_CMMA, kvm_s390_fixup_prefix, kvm_test_age_gfn, kvm_age_gfn) reads kvm->arch.gmap->asce *inside* the mmu_lock read-side. keyop is the only outlier. gmap->asce is mutated under write_lock(mmu_lock) by gmap_set_limit() and keyop might use a stale asce value for walking as KVM_S390_KEYOP and KVM_S390_VM_MEM_LIMIT_SIZE can run concurrently. This can result in memory corruption. Fixes: 0ee4ddc ("KVM: s390: Storage key manipulation IOCTL") Cc: stable@vger.kernel.org Signed-off-by: Christian Borntraeger Reviewed-by: Claudio Imbrenda Signed-off-by: Claudio Imbrenda Message-ID: <20260811153738.206885-2-borntraeger@linux.ibm.com> Signed-off-by: Greg Kroah-Hartman Changed files: arch/s390/kvm/kvm-s390.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=ae452b990e0544425f77045351c56e77158858e7 ====================================================================== DETAILED REPORT METHODOLOGY ====================================================================== The original Linux kernel CVE announcement for CVE-2026-89919 can be found here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89919 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:L/I:L/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: 5 Paranoid ActionableScore: 6 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: YES 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).