CVE-2026-97526
UnknownSummary
In the Linux kernel, the PMU PAI support for s390 lacked allocation of per-CPU data structures for CPUs added via hotplug. Running 'perf stat -e pai_crypto/CRYPTO_ALL/ -- <command>' while a CPU was being brought online caused pai_add() to dereference a NULL pointer and panic the kernel. CPU hotplug support (add and remove) was added to create the required per-CPU infrastructure.
Risk Assessment
The vulnerability can cause a kernel panic (denial of service) on s390 systems with PMU PAI enabled when a CPU is hotplugged online during a perf run. It requires local access and specific configuration, so the risk to a typical organization is limited.
Recommendation
Update the Linux kernel to a version containing the fix for CVE-2026-97526. If updating is not possible, avoid running perf with PMU PAI concurrently with CPU hotplug operations on s390 systems.
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Original NVD description (English source)
In the Linux kernel, the following vulnerability has been resolved: s390/pai: Support CPU hotplug for PMU PAI The command 'perf stat -e pai_crypto/CRYPTO_ALL/ -- <command>' crashes the kernel when CPUs are hotplug added during that run. Root cause is the missing allocation of per-CPU data structures for that new CPU. 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 Currently without a CPU hotplug handler, that new CPU has no per-CPU data infrastructure. The scheduler runs PMU call back function pai_add() to install the PMU support for that CPU before the task is being scheduled on that new CPU. In pai_add() instructions mp = this_cpu_ptr(pai_root[idx].mapptr); cpump = mp->mapptr; return a NULL pointer and the result is a kernel panic as variable cpump is used inside that function. Add CPU hotplug support for CPU add and delete and create the necessary per-CPU data infrastructure during CPU hotplug add processing. Same for CPU hotplug remove. This is done when the CPU is offline to ensure the data structures are available when CPU is made online and tasks are scheduled on it. [[email protected]: fixup error path in pai_init()]
Vulnerability data from NVD (NIST) · CISA KEV · EPSS