bounded loops in ebpf. Does now the verifier check if the program is a DAG?

Question

Since bounded loop are now allowed in ebpf programs https://git.kernel.org/pub/scm/linux/kernel/git/davem/net-next.git/commit/?id=2589726d12a1b12eaaa93c7f1ea64287e383c7a5 does the verifier still check in the first pass if the program control flow is a Direct Acyclic Graph?

pchaigno pchaigno · Accepted Answer · 2019-09-07T12:14:17

Yes, it still does, and rejects programs with back-edges in two cases:

If the program is loaded by an unprivileged user. The env->allow_ptr_leaks boolean indicates a privileged user.
If the back-edge is performed using a call. Only normal jumps can make bounded loops (which doesn't mean you can't do a bpf-to-bpf call inside a bounded loop).