CODEWITHSUNDEEP
ckernelbpfebpf
Maicake
Maicake

Reputation: 1136

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

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?

Upvotes: 5

Views: 951

Answers (1)

pchaigno
pchaigno

Reputation: 13133

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).

Upvotes: 5

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