On Mon, Feb 5, 2024 at 7:02 AM Kumar Kartikeya Dwivedi <memxor@xxxxxxxxx> wrote:
>
> Allow transferring an imbalanced RCU lock state between subprog calls
> during verification. This allows patterns where a subprog call returns
> with an RCU lock held, or a subprog call releases an RCU lock held by
> the caller. Currently, the verifier would end up complaining if the RCU
> lock is not released when processing an exit from a subprog, which is
> non-ideal if its execution is supposed to be enclosed in an RCU read
> section of the caller.
>
> Instead, simply only check whether we are processing exit for frame#0
> and do not complain on an active RCU lock otherwise. We only need to
> update the check when processing BPF_EXIT insn, as copy_verifier_state
> is already set up to do the right thing.
>
> Suggested-by: David Vernet <void@xxxxxxxxxxxxx>
> Signed-off-by: Kumar Kartikeya Dwivedi <memxor@xxxxxxxxx>
Tested-by: Yafang Shao <laoar.shao@xxxxxxxxx>
> ---
> kernel/bpf/verifier.c | 3 +--
> 1 file changed, 1 insertion(+), 2 deletions(-)
>
> diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
> index 64fa188d00ad..993712b9996b 100644
> --- a/kernel/bpf/verifier.c
> +++ b/kernel/bpf/verifier.c
> @@ -17698,8 +17698,7 @@ static int do_check(struct bpf_verifier_env *env)
> return -EINVAL;
> }
>
> - if (env->cur_state->active_rcu_lock &&
> - !in_rbtree_lock_required_cb(env)) {
> + if (env->cur_state->active_rcu_lock && !env->cur_state->curframe) {
> verbose(env, "bpf_rcu_read_unlock is missing\n");
> return -EINVAL;
> }
> --
> 2.40.1
>
>
--
Regards
Yafang
