Re: [PATCH bpf-next] bpf: Emit verbose message when prog-specific btf_struct_access rejects a write

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

On 6/15/26 4:21 PM, Alexei Starovoitov wrote:
> From: Alexei Starovoitov <ast@kernel.org>
>
> When BPF_WRITE goes through a PTR_TO_BTF_ID register, check_ptr_to_btf_access()
> delegates to env->ops->btf_struct_access(). Most implementations
> (bpf_scx_btf_struct_access, tc_cls_act_btf_struct_access, etc.) return
> -EACCES for disallowed fields without logging anything, so the verifier
> rejects the program with an empty message. For example a scx program doing
>
>    1: R1=trusted_ptr_task_struct()
>    ...
>    4: (7b) *(u64 *)(r1 +0) = r2
>    verification time 83 usec
>    the program is rejected
>
> leaves the user guessing which field is off-limits.
> Emit verbose message.
>
> Signed-off-by: Alexei Starovoitov <ast@kernel.org>

Indeed, e.g. bpf_scx_btf_struct_access() does not emit any verifier log
for failure. So it makes sense to have a generic verifier log after
env->ops->btf_struct_access().

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