Re: [PATCH bpf-next v4 07/20] bpf: Refuse exception cleanup shapes bpf_throw() cannot dispatch

[Yonghong Song <yonghong.song@linux.dev>]

On 9/22/26 2:43 PM, Eduard Zingerman wrote:
> On Mon, 2026-09-21 at 20:45 -0700, Yonghong Song wrote:
>
> ...
>
>>> Why is it necessary to hand-roll a CFG traversal and a separate pass
>>> for this check? Given that bpf verifier state already maintains
>>> `unwinding' flag, the instructions properties can be checked from
>>> do_check_insn(), e.g.:
>>> - bpf_throw()               -- reject if unwinding
>>> - call to a throwing global -- reject if unwinding
>>> - bpf_unwind_resume()       -- require unwinding and the pad-owning frame
>>> - BPF_EXIT                  -- reject in the pad-owning frame, allow in callees
>>> - LD_{ABS,IND}              -- reject if unwinding
>>>
>>> I think that would take much less code, wdyt?

This indeed reduces amount of codes by more than 2/3 for this patch.

>> This is a good idea. Let me try. Thanks!
> Also, regarding the tail calls. It appears that the following chain
> can call bpf_throw from a landing pad:
>
>    bpf_throw() -> landing pad -> global procedure call -> tail call -> bpf_throw()
>
> would this work as expected?

Yes, it works. tail_call itself is the terminator as it is the main prog,
bpf_throw() won't cross main prog boundary.