Re: [PATCH bpf-next v4 03/13] bpf: Collect kfuncs after resolving program resources

On Wed, Aug 5, 2026 at 2:05 PM Kumar Kartikeya Dwivedi <[email protected]> wrote:
>
> The kfunc descriptors include argument prototypes generated while calls are
> collected. Some argument classifications need program auxiliary state derived
> from referenced maps, such as the arena associated with the program.
>
> This avoids a footgun in get_kfunc_arg_type() checks where we do
> validation on whether program has prog->aux->arena and it hasn't been
> resolved yet.
>
> check_and_resolve_insns() records used maps and populates that state. It must
> remain after bpf_check_btf_info(), which applies kernel-side CO-RE relocations,
> so that instruction validation and the program tag observe the relocated
> instruction stream.
>
> Move only add_kfuncs() after instruction and resource resolution. Subprogram
> discovery and validation remain before the full BTF phase because that phase
> needs the complete subprogram layout. Add a short comment describing the
> resource resolution phase at the call site.
>
> Signed-off-by: Kumar Kartikeya Dwivedi <[email protected]>

Reviewed-by: Amery Hung <[email protected]>

> ---
>  kernel/bpf/verifier.c | 11 ++++++-----
>  1 file changed, 6 insertions(+), 5 deletions(-)
>
> diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
> index 24b163c2bd63..b62e77949542 100644
> --- a/kernel/bpf/verifier.c
> +++ b/kernel/bpf/verifier.c
> @@ -20344,11 +20344,6 @@ int bpf_check(struct bpf_prog **prog, union bpf_attr *attr, bpfptr_t uattr,
>         if (ret < 0)
>                 goto skip_full_check;
>
> -       /* Collect the kfunc descriptors used during verification. */
> -       ret = add_kfuncs(env);
> -       if (ret < 0)
> -               goto skip_full_check;
> -
>         ret = check_subprogs(env);
>         if (ret < 0)
>                 goto skip_full_check;
> @@ -20358,10 +20353,16 @@ int bpf_check(struct bpf_prog **prog, union bpf_attr *attr, bpfptr_t uattr,
>         if (ret < 0)
>                 goto skip_full_check;
>
> +       /* Validate instructions and resolve the program's referenced resources. */
>         ret = check_and_resolve_insns(env);
>         if (ret < 0)
>                 goto skip_full_check;
>
> +       /* Build kfunc prototypes after resolving program resources. */
> +       ret = add_kfuncs(env);
> +       if (ret < 0)
> +               goto skip_full_check;
> +
>         if (bpf_prog_is_offloaded(env->prog->aux)) {
>                 ret = bpf_prog_offload_verifier_prep(env->prog);
>                 if (ret)
> --
> 2.53.0
>
>