CVE-2023-53563

A reference leak flaw was found in the Linux kernel's AMD P-state unit test driver in the CPU policy access logic. A local user can trigger this issue by loading the amd-pstate-ut driver, which acquires CPU policy references via cpufreq_cpu_get without releasing them via cpufreq_cpu_put. This causes other processes attempting to access the policy to block indefinitely, resulting in hung tasks and denial of service through system unresponsiveness.

The amd_pstate_ut_check_perf and amd_pstate_ut_check_freq functions in the unit test driver call cpufreq_cpu_get to obtain and mark the CPU policy as busy. However, these functions fail to call the corresponding cpufreq_cpu_put to release the reference. This violates the cpufreq reference counting protocol and causes any subsequent attempt to access the policy—such as during mode changes or driver unload—to wait indefinitely for the reference to be released. The most visible manifestation is when changing amd_pstate modes, where processes hang for over 120 seconds waiting for completion. Since this is a unit test driver rather than production code, the practical impact is limited to testing scenarios, though the hang can affect system stability when the driver is loaded.

The CVSS score(s) listed for this vulnerability do not reflect the associated product's status, and are included for informational purposes to better understand the severity of this vulnerability.

To mitigate this issue, prevent the amd_pstate_ut module from being loaded. See https://access.redhat.com/solutions/41278 for instructions on blacklisting kernel modules.