---
id: "CVE-2026-99125"
kind: "vulnerability"
aliases: ["CVE-2026-99125"]
title: "Linux kernel s390 PAI perf: double PMU stop call corrupts sampling state"
severity: "unknown"
cvss: null
epss: null
exploited: false
status: "open"
category: "infrastructure"
products: []
ecosystems: []
tags: ["ibm-z", "infrastructure", "linux-kernel", "s390"]
not_affected_if: ["non-s390-architecture"]
published_at: "2026-10-28T11:17:32+00:00"
first_seen_at: "2026-10-28T11:32:35+00:00"
updated_at: "2026-10-28T11:37:29+00:00"
sources: [{"source": "nvd", "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-99125", "first_seen_at": "2026-10-28T11:32:35+00:00"}]
---

# Linux kernel s390 PAI perf: double PMU stop call corrupts sampling state

The s390 PAI performance monitoring driver in the Linux kernel could receive two back-to-back PMU stop callbacks when sampling was throttled and a task was then removed from the CPU. The sources do not describe an attacker outcome beyond a kernel driver state fix.

_Summary, check and fix written by a model from the sources; labelled as such._

## How to check

- unknown

## Fix

- Update to a Linux kernel release that includes the upstream commit for s390/pai multiple PMU stop handling (the sources do not name a version).

## Timeline

- 2026-10-28T11:32:35+00:00 nvd https://nvd.nist.gov/vuln/detail/CVE-2026-99125

## From the sources

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

s390/pai: Handle multiple PMU stop callback invocations

Handle the following scenario:
The kernel protects itself against a very high sampling load and
throttles the sampling using:

  perf_event_throttle() --> PMU->stop()

Shortly later the scheduler may terminate the task and removes it from the
CPU. It again calls

  PMU->stop()

which results in two invocations of PMU->stop() called back to back.
Protect against this and check the PERF_HES_STOPPED bit on function
entry.  If it is already set return.
Clear bit PERF_HES_STOPPED in PMU->start().

Prohibit ioctl(fd, PERF_EVENT_IOC_PERIOD, ...) call for this event.
It sets perf_event::event_limit to a positive value and causes
perf_event_overflow() to invoke pai_stop() call back function when
perf_event::event_limit hits zero. This is not supported because the
sample events CRYPTO_ALL and NNPA_ALL are only taken at schedule out
of a task.

Use list_for_each_entry_safe() for safe iteration over syswide_list
in pai_have_samples().

---

_Free to read at a human pace. An API with keys and an MCP server are in preparation; early access: hello@infrastack.ai_