CVE-2024-57951 Information

Description

In the Linux kernel the following vulnerability has been resolved:

hrtimers: Handle CPU state correctly on hotplug

Consider a scenario where a CPU transitions from CPUHP_ONLINE to halfway through a CPU hotunplug down to CPUHP_HRTIMERS_PREPARE and then back to CPUHP_ONLINE:

Since hrtimers_prepare_cpu() does not run cpu_base.hres_active remains set to 1 throughout. However during a CPU unplug operation the tick and the clockevents are shut down at CPUHP_AP_TICK_DYING. On return to the online state for instance CFS incorrectly assumes that the hrtick is already active and the chance of the clockevent device to transition to oneshot mode is also lost forever for the CPU unless it goes back to a lower state than CPUHP_HRTIMERS_PREPARE once.

This round-trip reveals another issue; cpu_base.online is not set to 1 after the transition which appears as a WARN_ON_ONCE in enqueue_hrtimer().

Aside of that the bulk of the per CPU state is not reset either which means there are dangling pointers in the worst case.

Address this by adding a corresponding startup() callback which resets the stale per CPU state and sets the online flag.

[ tglx: Make the new callback unconditionally available remove the online modification in the prepare() callback and clear the remaining state in the starting callback instead of the prepare callback ]

Reference

https://git.kernel.org/stable/c/14984139f1f2768883332965db566ef26db609e7 https://git.kernel.org/stable/c/15b453db41d36184cf0ccc21e7df624014ab6a1a https://git.kernel.org/stable/c/2f8dea1692eef2b7ba6a256246ed82c365fdc686 https://git.kernel.org/stable/c/38492f6ee883c7b1d33338bf531a62cff69b4b28 https://git.kernel.org/stable/c/3d41dbf82e10c44e53ea602398ab002baec27e75 https://git.kernel.org/stable/c/95e4f62df23f4df1ce6ef897d44b8e23c260921a https://git.kernel.org/stable/c/a5cbbea145b400e40540c34816d16d36e0374fbc