Linux Kernel RISC-V PMU Flag Check Removal Vulnerability

A vulnerability exists in the Linux kernel's RISC-V performance monitoring unit (PMU) driver, specifically in the handling of performance events. The issue arises because the PMU driver fails to properly manage the PERF_HES_STOPPED flag after a performance event overflow, leading to unnecessary warnings. This problem was introduced in a previous commit that added throttling for performance events on RISC-V. When the PMU driver does not update the stopped flag, it can cause conflicts with the performance event handling, particularly during timer interrupts, which can trigger warnings about the PMU state. Other PMU drivers do not have this issue, indicating that the RISC-V PMU driver requires adjustment to align with standard practices.

Impact

The vulnerability causes a warning to be issued during performance event handling, indicating a mismanagement of the PMU state. This could potentially lead to incorrect performance event reporting or handling on RISC-V systems.

Reproduction

The vulnerability can be reproduced by allowing performance events to overflow on a RISC-V system. When the overflow occurs, the PMU driver does not update the PERF_HES_STOPPED flag, which can be verified by observing the absence of a stopped flag update after a performance event overflow. This mismanagement will trigger a warning the next time the PMU start function is called, such as during a timer interrupt.

Remediation

The vulnerability has been addressed in the Linux kernel. Users should upgrade to the latest version where this issue has been fixed.