netdev - Re: [PATCH bpf-next] bpf: explicitly size compatible_reg

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Date:   Wed, 23 Sep 2020 09:05:38 -0700
From:   Andrii Nakryiko <andrii.nakryiko@...il.com>
To:     Lorenz Bauer <lmb@...udflare.com>
Cc:     Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        kernel-team <kernel-team@...udflare.com>,
        Networking <netdev@...r.kernel.org>, bpf <bpf@...r.kernel.org>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH bpf-next] bpf: explicitly size compatible_reg_types

On Wed, Sep 23, 2020 at 9:03 AM Lorenz Bauer <lmb@...udflare.com> wrote:
>
> Arrays with designated initializers have an implicit length of the highest
> initialized value plus one. I used this to ensure that newly added entries
> in enum bpf_reg_type get a NULL entry in compatible_reg_types.
>
> This is difficult to understand since it requires knowledge of the
> peculiarities of designated initializers. Use __BPF_ARG_TYPE_MAX to size
> the array instead.
>
> Signed-off-by: Lorenz Bauer <lmb@...udflare.com>
> Suggested-by: Alexei Starovoitov <ast@...nel.org>
> ---

I like this more as well.

Acked-by: Andrii Nakryiko <andriin@...com>

>  kernel/bpf/verifier.c | 3 +--
>  1 file changed, 1 insertion(+), 2 deletions(-)
>
> diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
> index 15ab889b0a3f..d7c993ded26a 100644
> --- a/kernel/bpf/verifier.c
> +++ b/kernel/bpf/verifier.c
> @@ -4002,7 +4002,7 @@ static const struct bpf_reg_types const_map_ptr_types = { .types = { CONST_PTR_T
>  static const struct bpf_reg_types btf_ptr_types = { .types = { PTR_TO_BTF_ID } };
>  static const struct bpf_reg_types spin_lock_types = { .types = { PTR_TO_MAP_VALUE } };
>
> -static const struct bpf_reg_types *compatible_reg_types[] = {
> +static const struct bpf_reg_types *compatible_reg_types[__BPF_ARG_TYPE_MAX] = {
>         [ARG_PTR_TO_MAP_KEY]            = &map_key_value_types,
>         [ARG_PTR_TO_MAP_VALUE]          = &map_key_value_types,
>         [ARG_PTR_TO_UNINIT_MAP_VALUE]   = &map_key_value_types,
> @@ -4025,7 +4025,6 @@ static const struct bpf_reg_types *compatible_reg_types[] = {
>         [ARG_PTR_TO_ALLOC_MEM_OR_NULL]  = &alloc_mem_types,
>         [ARG_PTR_TO_INT]                = &int_ptr_types,
>         [ARG_PTR_TO_LONG]               = &int_ptr_types,
> -       [__BPF_ARG_TYPE_MAX]            = NULL,
>  };
>
>  static int check_reg_type(struct bpf_verifier_env *env, u32 regno,
> --
> 2.25.1
>