> On Nov 14, 2019, at 10:57 AM, Alexei Starovoitov <ast@xxxxxxxxxx> wrote:
>
> Allow FENTRY/FEXIT BPF programs to attach to other BPF programs of any type
> including their subprograms. This feature allows snooping on input and output
> packets in XDP, TC programs including their return values. In order to do that
> the verifier needs to track types not only of vmlinux, but types of other BPF
> programs as well. The verifier also needs to translate uapi/linux/bpf.h types
> used by networking programs into kernel internal BTF types used by FENTRY/FEXIT
> BPF programs. In some cases LLVM optimizations can remove arguments from BPF
> subprograms without adjusting BTF info that LLVM backend knows. When BTF info
> disagrees with actual types that the verifiers sees the BPF trampoline has to
> fallback to conservative and treat all arguments as u64. The FENTRY/FEXIT
> program can still attach to such subprograms, but it won't be able to recognize
> pointer types like 'struct sk_buff *' and it won't be able to pass them to
> bpf_skb_output() for dumping packets to user space. The FENTRY/FEXIT program
> would need to use bpf_probe_read_kernel() instead.
>
> The BPF_PROG_LOAD command is extended with attach_prog_fd field. When it's set
> to zero the attach_btf_id is one vmlinux BTF type ids. When attach_prog_fd
> points to previously loaded BPF program the attach_btf_id is BTF type id of
> main function or one of its subprograms.
>
> Signed-off-by: Alexei Starovoitov <ast@xxxxxxxxxx>
Acked-by: Song Liu <songliubraving@xxxxxx>
[...]
> diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c
> index 4620267b186e..40efde5eedcb 100644
> --- a/kernel/bpf/btf.c
> +++ b/kernel/bpf/btf.c
> @@ -3530,6 +3530,20 @@ btf_get_prog_ctx_type(struct bpf_verifier_log *log, struct btf *btf,
> return ctx_type;
> }
>
nit: maybe add a comment here or where we call btf_translate_to_vmlinux().
> +static int btf_translate_to_vmlinux(struct bpf_verifier_log *log,
> + struct btf *btf,
> + const struct btf_type *t,
> + enum bpf_prog_type prog_type)
> +{
