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

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;