netdev - Re: [PATCH 3/9] bpf: Add bpfwl tool to construct bpf whitelists

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Date:   Thu, 14 May 2020 15:20:19 -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>,
        Yonghong Song <yhs@...com>, Martin KaFai Lau <kafai@...com>,
        David Miller <davem@...hat.com>,
        John Fastabend <john.fastabend@...il.com>,
        Jesper Dangaard Brouer <hawk@...nel.org>,
        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 3/9] bpf: Add bpfwl tool to construct bpf whitelists

On Wed, May 6, 2020 at 6:30 AM Jiri Olsa <jolsa@...nel.org> wrote:
>
> This tool takes vmlinux object and whitelist directory on input
> and produces C source object with BPF whitelist data.
>
> The vmlinux object needs to have a BTF information compiled in.
>
> The whitelist directory is expected to contain files with helper
> names, where each file contains list of functions/probes that
> helper is allowed to be called from - whitelist.
>
> The bpfwl tool has following output:
>
>   $ bpfwl vmlinux dir
>   unsigned long d_path[] __attribute__((section(".BTF_whitelist_d_path"))) = \
>   { 24507, 24511, 24537, 24539, 24545, 24588, 24602, 24920 };

why long instead of int? btf_id is 4-byte one.

>
> Each array are sorted BTF ids of the functions provided in the
> helper file.
>
> Each array will be compiled into kernel and used during the helper
> check in verifier.
>
> Signed-off-by: Jiri Olsa <jolsa@...nel.org>
> ---
>  tools/bpf/bpfwl/Build    |  11 ++
>  tools/bpf/bpfwl/Makefile |  60 +++++++++
>  tools/bpf/bpfwl/bpfwl.c  | 285 +++++++++++++++++++++++++++++++++++++++
>  3 files changed, 356 insertions(+)
>  create mode 100644 tools/bpf/bpfwl/Build
>  create mode 100644 tools/bpf/bpfwl/Makefile
>  create mode 100644 tools/bpf/bpfwl/bpfwl.c

Sorry, I didn't want to nitpick on naming, honestly, but I think this
is actually harmful in the long run. bpfwl is incomprehensible name,
anyone reading link script would be like "what the hell is bpfwl?" Why
not bpf_build_whitelist or something with "whitelist" spelled out in
full?

>
> diff --git a/tools/bpf/bpfwl/Build b/tools/bpf/bpfwl/Build
> new file mode 100644
> index 000000000000..667e30d6ce79
> --- /dev/null
> +++ b/tools/bpf/bpfwl/Build
> @@ -0,0 +1,11 @@
> +bpfwl-y += bpfwl.o
> +bpfwl-y += rbtree.o
> +bpfwl-y += zalloc.o
> +

[...]

> +
> +struct func {
> +       char                    *name;
> +       unsigned long            id;

as mentioned above, btf_id is 4 byte

> +       struct rb_node           rb_node;
> +       struct list_head         list[];
> +};
> +

[...]

> +       btf = btf__parse_elf(vmlinux, NULL);
> +       err = libbpf_get_error(btf);
> +       if (err) {
> +               fprintf(stderr, "FAILED: load BTF from %s: %s",
> +                       vmlinux, strerror(err));
> +               return -1;
> +       }
> +
> +       nr = btf__get_nr_types(btf);
> +
> +       /* Iterate all the BTF types and resolve all the function IDs. */
> +       for (id = 0; id < nr; id++) {

It has to be `for (id = 1; id <= nr; id++)`. 0 is VOID type and not
included into nr_types. I know it's confusing, but.. life :)

> +               const struct btf_type *type;
> +               struct func *func;
> +               const char *str;
> +
> +               type = btf__type_by_id(btf, id);
> +               if (!type)
> +                       continue;
> +

[...]