CVE-2025-21895

/// Technical description

In the Linux kernel, the following vulnerability has been resolved:

perf/core: Order the PMU list to fix warning about unordered pmu_ctx_list

Syskaller triggers a warning due to prev_epc->pmu != next_epc->pmu in

perf_event_swap_task_ctx_data(). vmcore shows that two lists have the same

perf_event_pmu_context, but not in the same order.

The problem is that the order of pmu_ctx_list for the parent is impacted by

the time when an event/PMU is added. While the order for a child is

impacted by the event order in the pinned_groups and flexible_groups. So

the order of pmu_ctx_list in the parent and child may be different.

To fix this problem, insert the perf_event_pmu_context to its proper place

after iteration of the pmu_ctx_list.

The follow testcase can trigger above warning:

# perf record -e cycles --call-graph lbr -- taskset -c 3 ./a.out &

# perf stat -e cpu-clock,cs -p xxx // xxx is the pid of a.out

test.c

void main() {

int count = 0;

pid_t pid;

print

/// Remediation

Check the references section for vendor advisories, patches, and mitigation guidance. If immediate patching is not possible, review the CVSS vector to understand the attack surface and apply compensating controls such as network segmentation or access restrictions.

/// References