Re: [PATCH bpf-next v2 00/26] Resilient Queued Spin Lock

Peter Zijlstra
2025-02-10T09:31:35Z

On Thu, Feb 06, 2025 at 02:54:08AM -0800, Kumar Kartikeya Dwivedi wrote:

> Additionally, eBPF programs attached to different parts of the kernel
> can introduce new control flow into the kernel, which increases the
> likelihood of deadlocks in code not written to handle reentrancy. There
> have been multiple syzbot reports surfacing deadlocks in internal kernel
> code due to the diverse ways in which eBPF programs can be attached to
> different parts of the kernel. By switching the BPF subsystem’s lock
> usage to rqspinlock, all of these issues can be mitigated at runtime.

Only if the called stuff is using this new lock. IIRC we've had a number
of cases where eBPF was used to tie together 'normal' kernel functions
in a way that wasn't sound. You can't help there.

As an example, eBPF calling strncpy_from_user(), which ends up in fault
injection and badness happens -- this has been since fixed, but still.