netdev - Re: [PATCH bpf-next v2] libbpf: Add getter for pointer to data area for internal maps

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <CAEf4BzbEyYQeLEsw0tzYYHeKi+q7a+vxavya9O3jykwsH3ki9g@mail.gmail.com>
Date:   Fri, 27 Mar 2020 12:17:56 -0700
From:   Andrii Nakryiko <andrii.nakryiko@...il.com>
To:     Toke Høiland-Jørgensen <toke@...hat.com>
Cc:     Daniel Borkmann <daniel@...earbox.net>,
        Alexei Starovoitov <ast@...com>, bpf <bpf@...r.kernel.org>,
        Networking <netdev@...r.kernel.org>
Subject: Re: [PATCH bpf-next v2] libbpf: Add getter for pointer to data area
 for internal maps

On Fri, Mar 27, 2020 at 5:58 AM Toke Høiland-Jørgensen <toke@...hat.com> wrote:
>
> For internal maps (most notably the maps backing global variables), libbpf
> uses an internal mmaped area to store the data after opening the object.
> This data is subsequently copied into the kernel map when the object is
> loaded.
>
> This adds a getter for the pointer to that internal data store. This can be
> used to modify the data before it is loaded into the kernel, which is
> especially relevant for RODATA, which is frozen on load. This same pointer
> is already exposed to the auto-generated skeletons, so access to it is
> already API; this just adds a way to get at it without pulling in the full
> skeleton infrastructure.
>
> Signed-off-by: Toke Høiland-Jørgensen <toke@...hat.com>
> ---
> v2:
>   - Add per-map getter for data area instead of a global rodata getter for bpf_obj
>
> tools/lib/bpf/libbpf.c   | 9 +++++++++
>  tools/lib/bpf/libbpf.h   | 1 +
>  tools/lib/bpf/libbpf.map | 1 +
>  3 files changed, 11 insertions(+)
>
> diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
> index 085e41f9b68e..a0055f8908fd 100644
> --- a/tools/lib/bpf/libbpf.c
> +++ b/tools/lib/bpf/libbpf.c
> @@ -6756,6 +6756,15 @@ void *bpf_map__priv(const struct bpf_map *map)
>         return map ? map->priv : ERR_PTR(-EINVAL);
>  }
>
> +void *bpf_map__data_area(const struct bpf_map *map, size_t *size)

I'm not entirely thrilled about "data_area" name. This is entirely for
providing initial value for maps, so maybe something like
bpf_map__init_value() or something along those lines?

Actually, how about a different API altogether:

bpf_map__set_init_value(struct bpf_map *map, void *data, size_t size)?

Application will have to prepare data of correct size, which will be
copied to libbpf's internal storage. It also doesn't expose any of
internal pointer. I don't think extra memcopy is a big deal here.
Thoughts?


> +{
> +       if (map->mmaped && map->libbpf_type != LIBBPF_MAP_KCONFIG) {
> +               *size = map->def.value_size;
> +               return map->mmaped;
> +       }
> +       return NULL;
> +}
> +
>  bool bpf_map__is_offload_neutral(const struct bpf_map *map)
>  {
>         return map->def.type == BPF_MAP_TYPE_PERF_EVENT_ARRAY;
> diff --git a/tools/lib/bpf/libbpf.h b/tools/lib/bpf/libbpf.h
> index d38d7a629417..baef0d2f3205 100644
> --- a/tools/lib/bpf/libbpf.h
> +++ b/tools/lib/bpf/libbpf.h
> @@ -407,6 +407,7 @@ typedef void (*bpf_map_clear_priv_t)(struct bpf_map *, void *);
>  LIBBPF_API int bpf_map__set_priv(struct bpf_map *map, void *priv,
>                                  bpf_map_clear_priv_t clear_priv);
>  LIBBPF_API void *bpf_map__priv(const struct bpf_map *map);
> +LIBBPF_API void *bpf_map__data_area(const struct bpf_map *map, size_t *size);
>  LIBBPF_API int bpf_map__reuse_fd(struct bpf_map *map, int fd);
>  LIBBPF_API int bpf_map__resize(struct bpf_map *map, __u32 max_entries);
>  LIBBPF_API bool bpf_map__is_offload_neutral(const struct bpf_map *map);
> diff --git a/tools/lib/bpf/libbpf.map b/tools/lib/bpf/libbpf.map
> index 5129283c0284..258528045a85 100644
> --- a/tools/lib/bpf/libbpf.map
> +++ b/tools/lib/bpf/libbpf.map
> @@ -243,5 +243,6 @@ LIBBPF_0.0.8 {
>                 bpf_link__pin;
>                 bpf_link__pin_path;
>                 bpf_link__unpin;
> +               bpf_map__data_area;
>                 bpf_program__set_attach_target;
>  } LIBBPF_0.0.7;
> --
> 2.26.0
>