netdev - Re: [PATCH bpf-next v1 09/19] bpf: add PTR_TO_BTF_ID_OR

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Date:   Wed, 29 Apr 2020 13:46:26 -0700
From:   Andrii Nakryiko <andrii.nakryiko@...il.com>
To:     Yonghong Song <yhs@...com>
Cc:     Andrii Nakryiko <andriin@...com>, bpf <bpf@...r.kernel.org>,
        Martin KaFai Lau <kafai@...com>,
        Networking <netdev@...r.kernel.org>,
        Alexei Starovoitov <ast@...com>,
        Daniel Borkmann <daniel@...earbox.net>,
        Kernel Team <kernel-team@...com>
Subject: Re: [PATCH bpf-next v1 09/19] bpf: add PTR_TO_BTF_ID_OR_NULL support

On Mon, Apr 27, 2020 at 1:13 PM Yonghong Song <yhs@...com> wrote:
>
> Add bpf_reg_type PTR_TO_BTF_ID_OR_NULL support.
> For tracing/iter program, the bpf program context
> definition, e.g., for previous bpf_map target, looks like
>   struct bpf_iter_bpf_map {
>     struct bpf_dump_meta *meta;
>     struct bpf_map *map;
>   };
>
> The kernel guarantees that meta is not NULL, but
> map pointer maybe NULL. The NULL map indicates that all
> objects have been traversed, so bpf program can take
> proper action, e.g., do final aggregation and/or send
> final report to user space.
>
> Add btf_id_or_null_non0_off to prog->aux structure, to
> indicate that for tracing programs, if the context access
> offset is not 0, set to PTR_TO_BTF_ID_OR_NULL instead of
> PTR_TO_BTF_ID. This bit is set for tracing/iter program.
>
> Signed-off-by: Yonghong Song <yhs@...com>
> ---
>  include/linux/bpf.h   |  2 ++
>  kernel/bpf/btf.c      |  5 ++++-
>  kernel/bpf/verifier.c | 19 ++++++++++++++-----
>  3 files changed, 20 insertions(+), 6 deletions(-)
>

[...]

>
>  static bool reg_may_point_to_spin_lock(const struct bpf_reg_state *reg)
> @@ -410,7 +411,8 @@ static bool reg_type_may_be_refcounted_or_null(enum bpf_reg_type type)
>         return type == PTR_TO_SOCKET ||
>                 type == PTR_TO_SOCKET_OR_NULL ||
>                 type == PTR_TO_TCP_SOCK ||
> -               type == PTR_TO_TCP_SOCK_OR_NULL;
> +               type == PTR_TO_TCP_SOCK_OR_NULL ||
> +               type == PTR_TO_BTF_ID_OR_NULL;

BTF_ID is not considered to be refcounted for the purpose of verifier,
unless I'm missing something?

>  }
>
>  static bool arg_type_may_be_refcounted(enum bpf_arg_type type)
> @@ -462,6 +464,7 @@ static const char * const reg_type_str[] = {
>         [PTR_TO_TP_BUFFER]      = "tp_buffer",
>         [PTR_TO_XDP_SOCK]       = "xdp_sock",
>         [PTR_TO_BTF_ID]         = "ptr_",
> +       [PTR_TO_BTF_ID_OR_NULL] = "ptr_or_null_",
>  };
>

[...]