In the Linux kernel, the following vulnerability has been resolved: s390/cpum_cf: Handle CPU hotplug via prepare/dead callbacks The command 'perf stat -e cycles -- <command>' crashes the kernel when CPUs are hotplug added during that run. Root cause is the allocation of struct cpu_cf_events at first event initialization. The allocation is dynamic and the first event that has task context creates such a structure for each online CPU. This is not sufficient. CPUs may be offline during event creation and can be set online during the perf run time. For example commands # echo 0 > /sys/devices/system/cpu/cpu1/online # perf stat -e cycles -i -- stress-ng -t10s --matrix X # sleep 1 # echo 1 > /sys/devices/system/cpu/cpu1/online create an event for CPUs 0,2-X. Since the events are created with task-context, the scheduler will eventually schedule the program on CPU1. This CPU has not created and initialized any per CPU event infrastructure as that CPU was not online at the time of the perf invocation. Thus when the scheduler runs stress-ng on CPU1, the function cpumf_pmu_add() refers to a NULL pointer: struct cpu_cf_events *cpuhw = this_cpu_cfhw(); This function call is invoked after the task stress-ng has been made runnable on CPU1. And this_cpu_cfhw() returns NULL. The result is a panic: Unable to handle kernel pointer dereference in virtual kernel address space Failing address: 0000000000000000 TEID: 0000000000000483 .... Krnl PSW : 0404d00180000000 000003ef8291fd0c (cpumf_pmu_add+0x3c/0x80) .... Call Trace: [<000003ef8291fd0c>] cpumf_pmu_add+0x3c/0x80 [<000003ef82bb5e3e>] event_sched_in+0xae/0x190 [<000003ef82bb60d6>] merge_sched_in+0x1b6/0x390 [<000003ef82bb65b8>] visit_groups_merge.constprop.0.isra.0+0x308/0x5b0 [<000003ef82bb689a>] pmu_groups_sched_in+0x3a/0x50 [<000003ef82bb6a30>] ctx_sched_in+0x180/0x260 [<000003ef82bb780c>] perf_event_context_sched_in+0x11c/0x2d0 [<000003ef82bb79ee>] __perf_event_task_sched_in+0x2e/0xc0 [<000003ef82994834>] finish_task_switch.isra.0+0x1a4/0x250 .... Last Breaking-Event-Address: [<000003ef8291f1d8>] this_cpu_cfhw+0x38/0x40 The issue arises only in per-task context when the CPUMF facility is used and the scheduler picks a random CPU for such a process to run on. The scheduler enables the CPUMF infrastructure via PMU callback functions pmu::add() and pmu::del(). Introduce a CPU hotplug prepare/dead callback pair which creates and removes the per CPU counter data while the CPU is offline. Count the users which track every CPU (cpu == -1), that is perf_event_open() events with task context and /dev/hwctr device sessions, in the new counter cpu_cf_root::tskcnt, protected by pmc_reserve_mutex. This ensures the infrastructure is available when new CPU is selected to run the per-task context process. In cpum_cf_free_root() and cpum_cf_free_cpu() ensure the reference pointer to data structures is set to NULL before the data is freed to prevent interrupt handlers to access stale data. [gor@linux.ibm.com: change commit message]

The Linux/Unix host has one or more packages installed that are impacted by a vulnerability without a vendor supplied patch available.

  - s390/cpum_cf: Handle CPU hotplug via prepare/dead callbacks The command 'perf stat -e cycles -- <command>'     crashes the kernel when CPUs are hotplug added during that run. Root cause is the allocation of struct     cpu_cf_events at first event initialization. The allocation is dynamic and the first event that has task     context creates such a structure for each online CPU. This is not sufficient. CPUs may be offline during     event creation and can be set online during the perf run time. For example commands # echo 0 >     /sys/devices/system/cpu/cpu1/online # perf stat -e cycles -i -- stress-ng -t10s --matrix X # sleep 1 #     echo 1 > /sys/devices/system/cpu/cpu1/online create an event for CPUs 0,2-X. Since the events are created     with task-context, the scheduler will eventually schedule the program on CPU1. This CPU has not created     and initialized any per CPU event infrastructure as that CPU was not online at the time of the perf     invocation. Thus when the scheduler runs stress-ng on CPU1, the function cpumf_pmu_add() refers to a NULL     pointer: struct cpu_cf_events *cpuhw = this_cpu_cfhw(); This function call is invoked after the task     stress-ng has been made runnable on CPU1. And this_cpu_cfhw() returns NULL. The result is a panic: Unable     to handle kernel pointer dereference in virtual kernel address space Failing address: 0000000000000000     TEID: 0000000000000483 .... Krnl PSW : 0404d00180000000 000003ef8291fd0c (cpumf_pmu_add+0x3c/0x80) ....
    Call Trace: [<000003ef8291fd0c>] cpumf_pmu_add+0x3c/0x80 [<000003ef82bb5e3e>] event_sched_in+0xae/0x190     [<000003ef82bb60d6>] merge_sched_in+0x1b6/0x390 [<000003ef82bb65b8>]     visit_groups_merge.constprop.0.isra.0+0x308/0x5b0 [<000003ef82bb689a>] pmu_groups_sched_in+0x3a/0x50     [<000003ef82bb6a30>] ctx_sched_in+0x180/0x260 [<000003ef82bb780c>] perf_event_context_sched_in+0x11c/0x2d0     [<000003ef82bb79ee>] __perf_event_task_sched_in+0x2e/0xc0 [<000003ef82994834>]     finish_task_switch.isra.0+0x1a4/0x250 .... Last Breaking-Event-Address: [<000003ef8291f1d8>]     this_cpu_cfhw+0x38/0x40 The issue arises only in per-task context when the CPUMF facility is used and the     scheduler picks a random CPU for such a process to run on. The scheduler enables the CPUMF infrastructure     via PMU callback functions pmu::add() and pmu::del(). Introduce a CPU hotplug prepare/dead callback pair     which creates and removes the per CPU counter data while the CPU is offline. Count the users which track     every CPU (cpu == -1), that is perf_event_open() events with task context and /dev/hwctr device sessions,     in the new counter cpu_cf_root::tskcnt, protected by pmc_reserve_mutex. This ensures the infrastructure is     available when new CPU is selected to run the per-task context process. In cpum_cf_free_root() and     cpum_cf_free_cpu() ensure the reference pointer to data structures is set to NULL before the data is freed     to prevent interrupt handlers to access stale data. [gor@linux.ibm.com: change commit message]     (CVE-2026-89460)

Note that Nessus relies on the presence of the package as reported by the vendor.

ID	Name	Product	Family	Type	Severity
365525	Ubuntu 24.04 LTS : Linux kernel (Azure) vulnerabilities (USN-8918-1)	Nessus	Ubuntu Local Security Checks	Local	medium
365522	Ubuntu 24.04 LTS : Linux kernel vulnerabilities (USN-8917-1)	Nessus	Ubuntu Local Security Checks	Local	medium
362907	Debian dla-4817 : ata-modules-6.12.107+deb12-armmp-di - security update	Nessus	Debian Local Security Checks	Local	high
351155	Debian dsa-6528 : ata-modules-6.12.111+deb13-armmp-di - security update	Nessus	Debian Local Security Checks	Local	high
345061	Linux Distros Unpatched Vulnerability : CVE-2026-89460	Nessus	Misc.	Local	medium

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