Re: [PATCH dwarves v6 1/6] bpf, x86: Generate trampolines from bpf_tramp_links

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

On Fri, Apr 15, 2022 at 9:30 PM Kui-Feng Lee <kuifeng@fb.com> wrote:
>
> Replace struct bpf_tramp_progs with struct bpf_tramp_links to collect
> struct bpf_tramp_link(s) for a trampoline.  struct bpf_tramp_link
> extends bpf_link to act as a linked list node.
>
> arch_prepare_bpf_trampoline() accepts a struct bpf_tramp_links to
> collects all bpf_tramp_link(s) that a trampoline should call.
>
> Change BPF trampoline and bpf_struct_ops to pass bpf_tramp_links
> instead of bpf_tramp_progs.
>
> Signed-off-by: Kui-Feng Lee <kuifeng@fb.com>
> ---
>  arch/x86/net/bpf_jit_comp.c    | 36 +++++++++--------
>  include/linux/bpf.h            | 36 +++++++++++------
>  include/linux/bpf_types.h      |  1 +
>  include/uapi/linux/bpf.h       |  1 +
>  kernel/bpf/bpf_struct_ops.c    | 69 ++++++++++++++++++++++----------
>  kernel/bpf/syscall.c           | 23 ++++-------
>  kernel/bpf/trampoline.c        | 73 +++++++++++++++++++---------------
>  net/bpf/bpf_dummy_struct_ops.c | 37 ++++++++++++++---
>  tools/bpf/bpftool/link.c       |  1 +
>  tools/include/uapi/linux/bpf.h |  1 +
>  10 files changed, 175 insertions(+), 103 deletions(-)
>

[...]

> @@ -385,6 +399,7 @@ static int bpf_struct_ops_map_update_elem(struct bpf_map *map, void *key,
>         for_each_member(i, t, member) {
>                 const struct btf_type *mtype, *ptype;
>                 struct bpf_prog *prog;
> +               struct bpf_tramp_link *link;
>                 u32 moff;
>
>                 moff = __btf_member_bit_offset(t, member) / 8;
> @@ -438,16 +453,26 @@ static int bpf_struct_ops_map_update_elem(struct bpf_map *map, void *key,
>                         err = PTR_ERR(prog);
>                         goto reset_unlock;
>                 }
> -               st_map->progs[i] = prog;
>
>                 if (prog->type != BPF_PROG_TYPE_STRUCT_OPS ||
>                     prog->aux->attach_btf_id != st_ops->type_id ||
>                     prog->expected_attach_type != i) {
> +                       bpf_prog_put(prog);
>                         err = -EINVAL;
>                         goto reset_unlock;
>                 }
>
> -               err = bpf_struct_ops_prepare_trampoline(tprogs, prog,
> +               link = kzalloc(sizeof(*link), GFP_USER);

seems like you are leaking this link and all the links allocated in
previous successful iterations of this loop?

> +               if (!link) {
> +                       bpf_prog_put(prog);
> +                       err = -ENOMEM;
> +                       goto reset_unlock;
> +               }
> +               bpf_link_init(&link->link, BPF_LINK_TYPE_STRUCT_OPS,
> +                             &bpf_struct_ops_link_lops, prog);
> +               st_map->links[i] = &link->link;
> +
> +               err = bpf_struct_ops_prepare_trampoline(tlinks, link,
>                                                         &st_ops->func_models[i],
>                                                         image, image_end);
>                 if (err < 0)
> @@ -490,7 +515,7 @@ static int bpf_struct_ops_map_update_elem(struct bpf_map *map, void *key,
>         memset(uvalue, 0, map->value_size);
>         memset(kvalue, 0, map->value_size);
>  unlock:
> -       kfree(tprogs);
> +       kfree(tlinks);

so you'll need to free those links inside tlinks (or wherever else
they are stored)

>         mutex_unlock(&st_map->lock);
>         return err;
>  }
> @@ -545,9 +570,9 @@ static void bpf_struct_ops_map_free(struct bpf_map *map)
>  {
>         struct bpf_struct_ops_map *st_map = (struct bpf_struct_ops_map *)map;
>
> -       if (st_map->progs)
> +       if (st_map->links)
>                 bpf_struct_ops_map_put_progs(st_map);
> -       bpf_map_area_free(st_map->progs);
> +       bpf_map_area_free(st_map->links);
>         bpf_jit_free_exec(st_map->image);
>         bpf_map_area_free(st_map->uvalue);
>         bpf_map_area_free(st_map);

[...]

> @@ -105,10 +120,20 @@ int bpf_struct_ops_test_run(struct bpf_prog *prog, const union bpf_attr *kattr,
>         }
>         set_vm_flush_reset_perms(image);
>
> +       link = kzalloc(sizeof(*link), GFP_USER);
> +       if (!link) {
> +               err = -ENOMEM;
> +               goto out;
> +       }
> +       /* prog doesn't take the ownership of the reference from caller */
> +       bpf_prog_inc(prog);
> +       bpf_link_init(&link->link, BPF_LINK_TYPE_STRUCT_OPS, &bpf_struct_ops_link_lops, prog);
> +
>         op_idx = prog->expected_attach_type;
> -       err = bpf_struct_ops_prepare_trampoline(tprogs, prog,
> +       err = bpf_struct_ops_prepare_trampoline(tlinks, link,
>                                                 &st_ops->func_models[op_idx],
>                                                 image, image + PAGE_SIZE);
> +

nit: no need for extra empty line here

>         if (err < 0)
>                 goto out;
>
> @@ -124,7 +149,9 @@ int bpf_struct_ops_test_run(struct bpf_prog *prog, const union bpf_attr *kattr,
>  out:
>         kfree(args);
>         bpf_jit_free_exec(image);
> -       kfree(tprogs);
> +       if (link)
> +               bpf_link_put(&link->link);

you never to bpf_link_prime() and bpf_link_settle() for these "pseudo
links" for struct_ops, so there is no need for bpf_link_put(), it can
be just bpf_link_free(), right?

> +       kfree(tlinks);
>         return err;
>  }
>
> diff --git a/tools/bpf/bpftool/link.c b/tools/bpf/bpftool/link.c
> index 8fb0116f9136..6353a789322b 100644
> --- a/tools/bpf/bpftool/link.c
> +++ b/tools/bpf/bpftool/link.c
> @@ -23,6 +23,7 @@ static const char * const link_type_name[] = {
>         [BPF_LINK_TYPE_XDP]                     = "xdp",
>         [BPF_LINK_TYPE_PERF_EVENT]              = "perf_event",
>         [BPF_LINK_TYPE_KPROBE_MULTI]            = "kprobe_multi",
> +       [BPF_LINK_TYPE_STRUCT_OPS]               = "struct_ops",
>  };
>
>  static struct hashmap *link_table;
> diff --git a/tools/include/uapi/linux/bpf.h b/tools/include/uapi/linux/bpf.h
> index d14b10b85e51..a4f557338af7 100644
> --- a/tools/include/uapi/linux/bpf.h
> +++ b/tools/include/uapi/linux/bpf.h
> @@ -1013,6 +1013,7 @@ enum bpf_link_type {
>         BPF_LINK_TYPE_XDP = 6,
>         BPF_LINK_TYPE_PERF_EVENT = 7,
>         BPF_LINK_TYPE_KPROBE_MULTI = 8,
> +       BPF_LINK_TYPE_STRUCT_OPS = 9,
>
>         MAX_BPF_LINK_TYPE,
>  };
> --
> 2.30.2
>