Re: [PATCH v2 bpf-next 4/9] btf: support kernel parsing of BTF with kind layout

[Andrii Nakryiko <andrii.nakryiko@gmail.com>]

On Fri, Jun 16, 2023 at 10:18 AM Alan Maguire <alan.maguire@oracle.com> wrote:
>
> Use kind layout to parse BTF with unknown kinds that have a
> kind layout representation.
>
> Validate kind layout if present, and use it to parse BTF with
> unrecognized kinds. Reject BTF that contains a type
> of a kind that is not optional.
>
> Signed-off-by: Alan Maguire <alan.maguire@oracle.com>
> ---
>  kernel/bpf/btf.c | 102 +++++++++++++++++++++++++++++++++++++----------
>  1 file changed, 82 insertions(+), 20 deletions(-)
>
> diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c
> index bd2cac057928..ffe3926ea051 100644
> --- a/kernel/bpf/btf.c
> +++ b/kernel/bpf/btf.c
> @@ -257,6 +257,7 @@ struct btf {
>         struct btf_kfunc_set_tab *kfunc_set_tab;
>         struct btf_id_dtor_kfunc_tab *dtor_kfunc_tab;
>         struct btf_struct_metas *struct_meta_tab;
> +       struct btf_kind_layout *kind_layout;
>
>         /* split BTF support */
>         struct btf *base_btf;
> @@ -4965,22 +4966,41 @@ static s32 btf_check_meta(struct btf_verifier_env *env,
>                 return -EINVAL;
>         }
>
> -       if (BTF_INFO_KIND(t->info) > BTF_KIND_MAX ||
> -           BTF_INFO_KIND(t->info) == BTF_KIND_UNKN) {
> -               btf_verifier_log(env, "[%u] Invalid kind:%u",
> -                                env->log_type_id, BTF_INFO_KIND(t->info));
> -               return -EINVAL;
> -       }
> -
>         if (!btf_name_offset_valid(env->btf, t->name_off)) {
>                 btf_verifier_log(env, "[%u] Invalid name_offset:%u",
>                                  env->log_type_id, t->name_off);
>                 return -EINVAL;
>         }
>
> -       var_meta_size = btf_type_ops(t)->check_meta(env, t, meta_left);
> -       if (var_meta_size < 0)
> -               return var_meta_size;
> +       if (BTF_INFO_KIND(t->info) == BTF_KIND_UNKN) {
> +               btf_verifier_log(env, "[%u] Invalid kind:%u",
> +                                env->log_type_id, BTF_INFO_KIND(t->info));
> +               return -EINVAL;
> +       }
> +
> +       if (BTF_INFO_KIND(t->info) > BTF_KIND_MAX && env->btf->kind_layout &&
> +           (BTF_INFO_KIND(t->info) * sizeof(struct btf_kind_layout)) <
> +            env->btf->hdr.kind_layout_len) {
> +               struct btf_kind_layout *k = &env->btf->kind_layout[BTF_INFO_KIND(t->info)];
> +
> +               if (!(k->flags & BTF_KIND_LAYOUT_OPTIONAL)) {

same question as on previous patch, should kernel trust and handle
OPTIONAL flag?

I'd say let's drop it for now, doesn't seem worth the trouble

> +                       btf_verifier_log(env, "[%u] unknown but required kind %u",
> +                                        env->log_type_id,
> +                                        BTF_INFO_KIND(t->info));
> +                       return -EINVAL;
> +               }
> +               var_meta_size = sizeof(struct btf_type);
> +               var_meta_size += k->info_sz + (btf_type_vlen(t) * k->elem_sz);
> +       } else {
> +               if (BTF_INFO_KIND(t->info) > BTF_KIND_MAX) {
> +                       btf_verifier_log(env, "[%u] Invalid kind:%u",
> +                                        env->log_type_id, BTF_INFO_KIND(t->info));
> +                       return -EINVAL;
> +               }
> +               var_meta_size = btf_type_ops(t)->check_meta(env, t, meta_left);
> +               if (var_meta_size < 0)
> +                       return var_meta_size;
> +       }
>
>         meta_left -= var_meta_size;
>
> @@ -5155,7 +5175,8 @@ static int btf_parse_str_sec(struct btf_verifier_env *env)
>         start = btf->nohdr_data + hdr->str_off;
>         end = start + hdr->str_len;
>
> -       if (end != btf->data + btf->data_size) {
> +       if (hdr->hdr_len < sizeof(struct btf_header) &&
> +           end != btf->data + btf->data_size) {
>                 btf_verifier_log(env, "String section is not at the end");
>                 return -EINVAL;
>         }
> @@ -5176,9 +5197,41 @@ static int btf_parse_str_sec(struct btf_verifier_env *env)
>         return 0;
>  }
>
> +static int btf_parse_kind_layout_sec(struct btf_verifier_env *env)
> +{
> +       const struct btf_header *hdr = &env->btf->hdr;
> +       struct btf *btf = env->btf;
> +       void *start, *end;
> +
> +       if (hdr->hdr_len < sizeof(struct btf_header) ||
> +           hdr->kind_layout_len == 0)

let's make sure that kind_layout_off is zero in this case as well

> +               return 0;
> +
> +       /* Kind layout section must align to 4 bytes */
> +       if (hdr->kind_layout_off & (sizeof(u32) - 1)) {
> +               btf_verifier_log(env, "Unaligned kind_layout_off");
> +               return -EINVAL;
> +       }
> +       start = btf->nohdr_data + hdr->kind_layout_off;
> +       end = start + hdr->kind_layout_len;
> +
> +       if (hdr->kind_layout_len < sizeof(struct btf_kind_layout)) {

same as on libbpf side, more generally kind_layout_len should be a
multiple of sizeof(struct btf_kind_layout)

> +               btf_verifier_log(env, "Kind layout section is too small");
> +               return -EINVAL;
> +       }
> +       if (end != btf->data + btf->data_size) {
> +               btf_verifier_log(env, "Kind layout section is not at the end");
> +               return -EINVAL;
> +       }
> +       btf->kind_layout = start;
> +
> +       return 0;
> +}
> +

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