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

Kui-Feng Lee
2024-02-20T18:22:46Z

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().

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;