netdev - Re: [PATCH 05/11] bpf: Remove btf

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Message-ID: <CAEf4BzYw0VciF-7CS164Nk8LLnZ4odtdYQyX1MS4eWDN5WbcSg@mail.gmail.com>
Date:   Thu, 18 Jun 2020 18:10:29 -0700
From:   Andrii Nakryiko <andrii.nakryiko@...il.com>
To:     Jiri Olsa <jolsa@...nel.org>
Cc:     Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Networking <netdev@...r.kernel.org>, bpf <bpf@...r.kernel.org>,
        Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
        Martin KaFai Lau <kafai@...com>,
        David Miller <davem@...hat.com>,
        John Fastabend <john.fastabend@...il.com>,
        Wenbo Zhang <ethercflow@...il.com>,
        KP Singh <kpsingh@...omium.org>,
        Andrii Nakryiko <andriin@...com>,
        Brendan Gregg <bgregg@...flix.com>,
        Florent Revest <revest@...omium.org>,
        Al Viro <viro@...iv.linux.org.uk>
Subject: Re: [PATCH 05/11] bpf: Remove btf_id helpers resolving

On Tue, Jun 16, 2020 at 3:06 AM Jiri Olsa <jolsa@...nel.org> wrote:
>
> Now when we moved the helpers btf_id into .BTF_ids section,
> we can remove the code that resolve those IDs in runtime.
>
> Signed-off-by: Jiri Olsa <jolsa@...nel.org>
> ---

Nice! :)

BTW, have you looked at bpf_ctx_convert stuff? Would we be able to
replace it with your btfids thing as well?


>  kernel/bpf/btf.c | 88 +++---------------------------------------------
>  1 file changed, 4 insertions(+), 84 deletions(-)
>
> diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c
> index 58c9af1d4808..aea7b2cc8d26 100644
> --- a/kernel/bpf/btf.c
> +++ b/kernel/bpf/btf.c
> @@ -4049,96 +4049,16 @@ int btf_struct_access(struct bpf_verifier_log *log,
>         return -EINVAL;
>  }
>

[...]

>  int btf_resolve_helper_id(struct bpf_verifier_log *log,
>                           const struct bpf_func_proto *fn, int arg)
>  {
> -       int *btf_id = &fn->btf_id[arg];
> -       int ret;
> -
>         if (fn->arg_type[arg] != ARG_PTR_TO_BTF_ID)
>                 return -EINVAL;
>
> -       ret = READ_ONCE(*btf_id);
> -       if (ret)
> -               return ret;
> -       /* ok to race the search. The result is the same */
> -       ret = __btf_resolve_helper_id(log, fn->func, arg);
> -       if (!ret) {
> -               /* Function argument cannot be type 'void' */
> -               bpf_log(log, "BTF resolution bug\n");
> -               return -EFAULT;
> -       }
> -       WRITE_ONCE(*btf_id, ret);
> -       return ret;
> +       if (WARN_ON_ONCE(!fn->btf_id))
> +               return -EINVAL;
> +
> +       return fn->btf_id[arg];

It probably would be a good idea to add some sanity checking here,
making sure that btf_id is >0 (void is never a right type) and <=
nr_types in vmlinux_btf?

>  }
>
>  static int __get_type_size(struct btf *btf, u32 btf_id,
> --
> 2.25.4
>