[External] Re: [PATCH bpf-next v2 1/9] bpf: tracing: add support to record and check the accessed args

[梦龙董]

On Tue, Mar 12, 2024 at 9:46 AM Alexei Starovoitov
<alexei.starovoitov at gmail.com> wrote:
>
> On Mon, Mar 11, 2024 at 2:34 AM Menglong Dong
> <dongmenglong.8 at bytedance.com> 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 at bytedance.com>
> > ---
> >  include/linux/bpf.h |   4 ++
> >  kernel/bpf/btf.c    | 108 +++++++++++++++++++++++++++++++++++++++++++-
> >  2 files changed, 110 insertions(+), 2 deletions(-)
> >
> > diff --git a/include/linux/bpf.h b/include/linux/bpf.h
> > index 95e07673cdc1..0f677fdcfcc7 100644
> > --- a/include/linux/bpf.h
> > +++ b/include/linux/bpf.h
> > @@ -1461,6 +1461,7 @@ 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;
> > @@ -2565,6 +2566,9 @@ 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 170d017e8e4a..c2a0299d4358 100644
> > --- a/kernel/bpf/btf.c
> > +++ b/kernel/bpf/btf.c
> > @@ -6125,19 +6125,24 @@ static bool is_int_ptr(struct btf *btf, const struct btf_type *t)
> >  }
> >
> >  static u32 get_ctx_arg_idx(struct btf *btf, const struct btf_type *func_proto,
> > -                          int off)
> > +                          int off, int *aligned_idx)
> >  {
> >         const struct btf_param *args;
> >         const struct btf_type *t;
> >         u32 offset = 0, nr_args;
> >         int i;
> >
> > +       if (aligned_idx)
> > +               *aligned_idx = -ENOENT;
> > +
> >         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 (aligned_idx && offset == off)
> > +                       *aligned_idx = i;
> >                 t = btf_type_skip_modifiers(btf, args[i].type, NULL);
> >                 offset += btf_type_is_ptr(t) ? 8 : roundup(t->size, 8);
> >                 if (off < offset)
> > @@ -6207,7 +6212,7 @@ bool btf_ctx_access(int off, int size, enum bpf_access_type type,
> >                         tname, off);
> >                 return false;
> >         }
> > -       arg = get_ctx_arg_idx(btf, t, off);
> > +       arg = get_ctx_arg_idx(btf, t, off, NULL);
> >         args = (const struct btf_param *)(t + 1);
> >         /* if (t == NULL) Fall back to default BPF prog with
> >          * MAX_BPF_FUNC_REG_ARGS u64 arguments.
> > @@ -6217,6 +6222,9 @@ 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);
>
> What do you need this aligned_idx for ?
> I'd expect that above "accessed_args |= (1 << arg);" is enough.
>

Which aligned_idx? No aligned_idx in the btf_ctx_access(), and
aligned_idx is only used in the btf_check_func_part_match().

In the btf_check_func_part_match(), I need to compare the
t1->args[i] and t2->args[j], which have the same offset. And
the aligned_idx is to find the "j" according to the offset of
t1->args[i].

> >         }
> >
> >         if (arg > nr_args) {
> > @@ -7024,6 +7032,102 @@ 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;
> > +}
> > +
> > +/* 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)
>
> This is way too much copy paste.
> Please share the code with btf_check_func_type_match.

Okay!

Thanks!
Menglong Dong