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

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Message-ID: <ZdTe8LteoqR43d4q@krava>
Date: Tue, 20 Feb 2024 18:18:40 +0100
From: Jiri Olsa <olsajiri@...il.com>
To: Menglong Dong <dongmenglong.8@...edance.com>
Cc: andrii@...nel.org, ast@...nel.org, daniel@...earbox.net,
	martin.lau@...ux.dev, eddyz87@...il.com, song@...nel.org,
	yonghong.song@...ux.dev, john.fastabend@...il.com,
	kpsingh@...nel.org, sdf@...gle.com, haoluo@...gle.com,
	mykolal@...com, shuah@...nel.org, mcoquelin.stm32@...il.com,
	alexandre.torgue@...s.st.com, thinker.li@...il.com,
	zhoufeng.zf@...edance.com, davemarchevsky@...com, dxu@...uu.xyz,
	linux-kernel@...r.kernel.org, bpf@...r.kernel.org,
	linux-kselftest@...r.kernel.org,
	linux-stm32@...md-mailman.stormreply.com,
	linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH bpf-next 1/5] bpf: tracing: add support to record and
 check the accessed args

On Tue, Feb 20, 2024 at 11:51:01AM +0800, Menglong Dong wrote:

SNIP

> +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 function is similar to btf_check_func_type_match(), except that it
> + * only compare some function args of the function prototype t1 and t2.
> + */

could we reuse btf_check_func_type_match instead? perhaps just
adding extra argument with arguments bitmap to it?

jirka

> +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;
> -- 
> 2.39.2
>