Re: [External] Re: [PATCH bpf-next 1/5] bpf: tracing: add support to record and check the accessed args

[梦龙董 <dongmenglong.8@bytedance.com>]

On Wed, Feb 21, 2024 at 2:22 AM Kui-Feng Lee <sinquersw@gmail.com> wrote:
>
>
>
> On 2/19/24 19:51, Menglong Dong wrote:
> > In this commit, we add the 'accessed_args' field to struct bpf_prog_aux,
> > which is used to record the accessed index of the function args in
> > btf_ctx_access().
> >
> > Meanwhile, we add the function btf_check_func_part_match() to compare the
> > accessed function args of two function prototype. This function will be
> > used in the following commit.
> >
> > Signed-off-by: Menglong Dong <dongmenglong.8@bytedance.com>
> > ---
> >   include/linux/bpf.h |   4 ++
> >   kernel/bpf/btf.c    | 121 ++++++++++++++++++++++++++++++++++++++++++++
> >   2 files changed, 125 insertions(+)
> >
> > diff --git a/include/linux/bpf.h b/include/linux/bpf.h
> > index c7aa99b44dbd..0225b8dbdd9d 100644
> > --- a/include/linux/bpf.h
> > +++ b/include/linux/bpf.h
> > @@ -1464,6 +1464,7 @@ struct bpf_prog_aux {
> >       const struct btf_type *attach_func_proto;
> >       /* function name for valid attach_btf_id */
> >       const char *attach_func_name;
> > +     u64 accessed_args;
> >       struct bpf_prog **func;
> >       void *jit_data; /* JIT specific data. arch dependent */
> >       struct bpf_jit_poke_descriptor *poke_tab;
> > @@ -2566,6 +2567,9 @@ struct bpf_reg_state;
> >   int btf_prepare_func_args(struct bpf_verifier_env *env, int subprog);
> >   int btf_check_type_match(struct bpf_verifier_log *log, const struct bpf_prog *prog,
> >                        struct btf *btf, const struct btf_type *t);
> > +int btf_check_func_part_match(struct btf *btf1, const struct btf_type *t1,
> > +                           struct btf *btf2, const struct btf_type *t2,
> > +                           u64 func_args);
> >   const char *btf_find_decl_tag_value(const struct btf *btf, const struct btf_type *pt,
> >                                   int comp_idx, const char *tag_key);
> >   int btf_find_next_decl_tag(const struct btf *btf, const struct btf_type *pt,
> > diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c
> > index 6ff0bd1a91d5..3a6931402fe4 100644
> > --- a/kernel/bpf/btf.c
> > +++ b/kernel/bpf/btf.c
> > @@ -6203,6 +6203,9 @@ bool btf_ctx_access(int off, int size, enum bpf_access_type type,
> >               /* skip first 'void *__data' argument in btf_trace_##name typedef */
> >               args++;
> >               nr_args--;
> > +             prog->aux->accessed_args |= (1 << (arg + 1));
> > +     } else {
> > +             prog->aux->accessed_args |= (1 << arg);
> >       }
> >
> >       if (arg > nr_args) {
> > @@ -7010,6 +7013,124 @@ int btf_check_type_match(struct bpf_verifier_log *log, const struct bpf_prog *pr
> >       return btf_check_func_type_match(log, btf1, t1, btf2, t2);
> >   }
> >
> > +static u32 get_ctx_arg_total_size(struct btf *btf, const struct btf_type *t)
> > +{
> > +     const struct btf_param *args;
> > +     u32 size = 0, nr_args;
> > +     int i;
> > +
> > +     nr_args = btf_type_vlen(t);
> > +     args = (const struct btf_param *)(t + 1);
> > +     for (i = 0; i < nr_args; i++) {
> > +             t = btf_type_skip_modifiers(btf, args[i].type, NULL);
> > +             size += btf_type_is_ptr(t) ? 8 : roundup(t->size, 8);
> > +     }
> > +
> > +     return size;
> > +}
> > +
> > +static int get_ctx_arg_idx_aligned(struct btf *btf, const struct btf_type *t,
> > +                                int off)
> > +{
> > +     const struct btf_param *args;
> > +     u32 offset = 0, nr_args;
> > +     int i;
> > +
> > +     nr_args = btf_type_vlen(t);
> > +     args = (const struct btf_param *)(t + 1);
> > +     for (i = 0; i < nr_args; i++) {
> > +             if (offset == off)
> > +                     return i;
> > +
> > +             t = btf_type_skip_modifiers(btf, args[i].type, NULL);
> > +             offset += btf_type_is_ptr(t) ? 8 : roundup(t->size, 8);
> > +             if (offset > off)
> > +                     return -1;
> > +     }
> > +     return -1;
> > +}
>
> This one is very similar to get_ctx_arg_idx().
> How about to refactor get_ctx_arg_idx() and share the code
> between get_ctx_arg_idx() and get_ctx_arg_idx_aligned().
>

This seems to work, I'll combine them in the next version.

Thanks for the example code!
Menglong Dong

> For example,
>
> -static u32 get_ctx_arg_idx(struct btf *btf, const struct btf_type
> *func_proto,
> -                          int off)
> +static u32 _get_ctx_arg_idx(struct btf *btf, const struct btf_type
> *func_proto,
> +                          int off, u32 *arg_off)
>   {
>          const struct btf_param *args;
>          const struct btf_type *t;
>          u32 offset = 0, nr_args;
>          int i;
>
>          if (!func_proto)
>                  return off / 8;
>
>          nr_args = btf_type_vlen(func_proto);
>          args = (const struct btf_param *)(func_proto + 1);
>          for (i = 0; i < nr_args; i++) {
> +               if (arg_off)
> +                       *arg_off = offset;
>                  t = btf_type_skip_modifiers(btf, args[i].type, NULL);
>                  offset += btf_type_is_ptr(t) ? 8 : roundup(t->size, 8);
>                  if (off < offset)
>                          return i;
>          }
>
> +       if (arg_off)
> +               *arg_off = offset;
>          t = btf_type_skip_modifiers(btf, func_proto->type, NULL);
>          offset += btf_type_is_ptr(t) ? 8 : roundup(t->size, 8);
>          if (off < offset)
>                  return nr_args;
>
>          return nr_args + 1;
>   }
>
> +static u32 get_ctx_arg_idx(struct btf *btf, const struct btf_type
> *func_proto,
> +                          int off)
> +{
> +       return _get_ctx_arg_idx(btf, func_proto, off, NULL);
> +}
> +
> +static u32 get_ctx_arg_idx_aligned(struct btf *btf,
> +                                  const struct btf_type *func_proto,
> +                                  int off)
> +{
> +       u32 arg_off;
> +       u32 arg_idx = _get_ctx_arg_idx(btf, func_proto, off, &arg_off);
> +       return arg_off == off ? arg_idx : -1;
> +}
> +
>
> > +
> > +/* This function is similar to btf_check_func_type_match(), except that it
> > + * only compare some function args of the function prototype t1 and t2.
> > + */
> > +int btf_check_func_part_match(struct btf *btf1, const struct btf_type *func1,
> > +                           struct btf *btf2, const struct btf_type *func2,
> > +                           u64 func_args)
> > +{
> > +     const struct btf_param *args1, *args2;
> > +     u32 nargs1, i, offset = 0;
> > +     const char *s1, *s2;
> > +
> > +     if (!btf_type_is_func_proto(func1) || !btf_type_is_func_proto(func2))
> > +             return -EINVAL;
> > +
> > +     args1 = (const struct btf_param *)(func1 + 1);
> > +     args2 = (const struct btf_param *)(func2 + 1);
> > +     nargs1 = btf_type_vlen(func1);
> > +
> > +     for (i = 0; i <= nargs1; i++) {
> > +             const struct btf_type *t1, *t2;
> > +
> > +             if (!(func_args & (1 << i)))
> > +                     goto next;
> > +
> > +             if (i < nargs1) {
> > +                     int t2_index;
> > +
> > +                     /* get the index of the arg corresponding to args1[i]
> > +                      * by the offset.
> > +                      */
> > +                     t2_index = get_ctx_arg_idx_aligned(btf2, func2,
> > +                                                        offset);
> > +                     if (t2_index < 0)
> > +                             return -EINVAL;
> > +
> > +                     t1 = btf_type_skip_modifiers(btf1, args1[i].type, NULL);
> > +                     t2 = btf_type_skip_modifiers(btf2, args2[t2_index].type,
> > +                                                  NULL);
> > +             } else {
> > +                     /* i == nargs1, this is the index of return value of t1 */
> > +                     if (get_ctx_arg_total_size(btf1, func1) !=
> > +                         get_ctx_arg_total_size(btf2, func2))
> > +                             return -EINVAL;
> > +
> > +                     /* check the return type of t1 and t2 */
> > +                     t1 = btf_type_skip_modifiers(btf1, func1->type, NULL);
> > +                     t2 = btf_type_skip_modifiers(btf2, func2->type, NULL);
> > +             }
> > +
> > +             if (t1->info != t2->info ||
> > +                 (btf_type_has_size(t1) && t1->size != t2->size))
> > +                     return -EINVAL;
> > +             if (btf_type_is_int(t1) || btf_is_any_enum(t1))
> > +                     goto next;
> > +
> > +             if (btf_type_is_struct(t1))
> > +                     goto on_struct;
> > +
> > +             if (!btf_type_is_ptr(t1))
> > +                     return -EINVAL;
> > +
> > +             t1 = btf_type_skip_modifiers(btf1, t1->type, NULL);
> > +             t2 = btf_type_skip_modifiers(btf2, t2->type, NULL);
> > +             if (!btf_type_is_struct(t1) || !btf_type_is_struct(t2))
> > +                     return -EINVAL;
> > +
> > +on_struct:
> > +             s1 = btf_name_by_offset(btf1, t1->name_off);
> > +             s2 = btf_name_by_offset(btf2, t2->name_off);
> > +             if (strcmp(s1, s2))
> > +                     return -EINVAL;
> > +next:
> > +             if (i < nargs1) {
> > +                     t1 = btf_type_skip_modifiers(btf1, args1[i].type, NULL);
> > +                     offset += btf_type_is_ptr(t1) ? 8 : roundup(t1->size, 8);
> > +             }
> > +     }
> > +
> > +     return 0;
> > +}
> > +
> >   static bool btf_is_dynptr_ptr(const struct btf *btf, const struct btf_type *t)
> >   {
> >       const char *name;