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

Alexei Starovoitov
2024-03-12T01:46:33Z

On Mon, Mar 11, 2024 at 2:34 AM Menglong Dong
<dongmenglong.8@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@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.

> }
>
> 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.