CVE-2026-97526 s390/pai: Support CPU hotplug for PMU PAI
A local attacker can cause a kernel panic via null pointer dereference in the s390 PAI PMU driver during CPU hotplug events.
- Exploited in the wild
- Not known
- Login needed
- Any signed-in user
- Attackable
- Local or same network only
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-97526?
CVE-2026-97526 is a vulnerability in Linux, published on 25 Sep 2026. It can only be exploited from the same machine or local network, with no action from the victim.
Official description
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()]
Which versions are affected by CVE-2026-97526?
How do I fix CVE-2026-97526?
Apply the vendor's patch.
Is CVE-2026-97526 being exploited?
There is no known exploitation of CVE-2026-97526 in the wild and no public exploit code.
Sources
Also known as BELL-CVE-2026-97526, DEBIAN-CVE-2026-97526, GHSA-4mg4-96g4-2j54, UBUNTU-CVE-2026-97526.