Show the rejected function name when attaching tracing programs to
functions in deny list.

With this change, we know why tracing programs can't attach to functions
like migrate_disable() from log.

$ ./fentry
libbpf: prog 'migrate_disable': BPF program load failed: -EINVAL
libbpf: prog 'migrate_disable': -- BEGIN PROG LOAD LOG --
Attaching tracing programs to function 'migrate_disable' is rejected.

Suggested-by: Leon Hwang <leon.hwang@linux.dev>
Signed-off-by: KaFai Wan <kafai.wan@linux.dev>
---
 kernel/bpf/verifier.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 00d287814f12..c24c0d57e595 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -23942,6 +23942,8 @@ static int check_attach_btf_id(struct bpf_verifier_env *env)
 			return ret;
 	} else if (prog->type == BPF_PROG_TYPE_TRACING &&
 		   btf_id_set_contains(&btf_id_deny, btf_id)) {
+		verbose(env, "Attaching tracing programs to function '%s' is rejected.\n",
+			tgt_info.tgt_name);
 		return -EINVAL;
 	} else if ((prog->expected_attach_type == BPF_TRACE_FEXIT ||
 		   prog->expected_attach_type == BPF_MODIFY_RETURN) &&
-- 
2.43.0

On 7/22/25 8:34 AM, KaFai Wan wrote:
> Show the rejected function name when attaching tracing programs to
> functions in deny list.
>
> With this change, we know why tracing programs can't attach to functions
> like migrate_disable() from log.
>
> $ ./fentry
> libbpf: prog 'migrate_disable': BPF program load failed: -EINVAL
> libbpf: prog 'migrate_disable': -- BEGIN PROG LOAD LOG --
> Attaching tracing programs to function 'migrate_disable' is rejected.
>
> Suggested-by: Leon Hwang <leon.hwang@linux.dev>
> Signed-off-by: KaFai Wan <kafai.wan@linux.dev>

Acked-by: Yonghong Song <yonghong.song@linux.dev>

On Tue, Jul 22, 2025 at 11:35 PM KaFai Wan <kafai.wan@linux.dev> wrote:
>
> Show the rejected function name when attaching tracing programs to
> functions in deny list.
>
> With this change, we know why tracing programs can't attach to functions
> like migrate_disable() from log.
>
> $ ./fentry
> libbpf: prog 'migrate_disable': BPF program load failed: -EINVAL
> libbpf: prog 'migrate_disable': -- BEGIN PROG LOAD LOG --
> Attaching tracing programs to function 'migrate_disable' is rejected.
>
> Suggested-by: Leon Hwang <leon.hwang@linux.dev>
> Signed-off-by: KaFai Wan <kafai.wan@linux.dev>

Acked-by: Yafang Shao <laoar.shao@gmail.com>

> ---
>  kernel/bpf/verifier.c | 2 ++
>  1 file changed, 2 insertions(+)
>
> diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
> index 00d287814f12..c24c0d57e595 100644
> --- a/kernel/bpf/verifier.c
> +++ b/kernel/bpf/verifier.c
> @@ -23942,6 +23942,8 @@ static int check_attach_btf_id(struct bpf_verifier_env *env)
>                         return ret;
>         } else if (prog->type == BPF_PROG_TYPE_TRACING &&
>                    btf_id_set_contains(&btf_id_deny, btf_id)) {
> +               verbose(env, "Attaching tracing programs to function '%s' is rejected.\n",
> +                       tgt_info.tgt_name);
>                 return -EINVAL;
>         } else if ((prog->expected_attach_type == BPF_TRACE_FEXIT ||
>                    prog->expected_attach_type == BPF_MODIFY_RETURN) &&
> --
> 2.43.0
>


-- 
Regards
Yafang