s390/pai: Handle multiple PMU stop callback invocations

Overview

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().

Affected

• Linux >= 9f66572f2889a5e72a9d7e17787e52f03b1f7bd8 < cf348ec613f75b9774291e47b804fd7010835a6c
• Linux >= 9f66572f2889a5e72a9d7e17787e52f03b1f7bd8 < f3110e969ad226ffbb2d9b4bf5387e68d0d9ef40
• Linux 6.11

Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.