Re: [PATCH bpf-next v2 05/14] bpf: Add support for custom exception callbacks

[Martin KaFai Lau <martin.lau@linux.dev>]

On 8/9/23 4:41 AM, Kumar Kartikeya Dwivedi wrote:
> diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
> index d0f6c984272b..9d67d0633c59 100644
> --- a/kernel/bpf/verifier.c
> +++ b/kernel/bpf/verifier.c
> @@ -2457,6 +2457,73 @@ static int add_subprog(struct bpf_verifier_env *env, int off)
>   	return env->subprog_cnt - 1;
>   }
>   
> +static int bpf_find_exception_callback_insn_off(struct bpf_verifier_env *env)
> +{
> +	struct bpf_prog_aux *aux = env->prog->aux;
> +	struct btf *btf = aux->btf;
> +	const struct btf_type *t;
> +	const char *name;
> +	u32 main_btf_id;
> +	int ret, i, j;
> +
> +	/* Non-zero func_info_cnt implies valid btf */
> +	if (!aux->func_info_cnt)
> +		return 0;
> +	main_btf_id = aux->func_info[0].type_id;
> +
> +	t = btf_type_by_id(btf, main_btf_id);
> +	if (!t) {
> +		verbose(env, "invalid btf id for main subprog in func_info\n");
> +		return -EINVAL;
> +	}
> +
> +	name = btf_find_decl_tag_value(btf, t, -1, "exception_callback:");
> +	if (IS_ERR(name)) {
> +		ret = PTR_ERR(name);
> +		/* If there is no tag present, there is no exception callback */
> +		if (ret == -ENOENT)
> +			ret = 0;
> +		else if (ret == -EEXIST)
> +			verbose(env, "multiple exception callback tags for main subprog\n");
> +		return ret;
> +	}
> +
> +	ret = -ENOENT;
> +	for (i = 0; i < btf_nr_types(btf); i++) {
> +		t = btf_type_by_id(btf, i);
> +		if (!btf_type_is_func(t))
> +			continue;
> +		if (strcmp(name, btf_name_by_offset(btf, t->name_off)))
> +			continue;

nit. btf_find_by_name_kind() could be used here.


> +		if (btf_func_linkage(t) != BTF_FUNC_GLOBAL) {
> +			verbose(env, "exception callback '%s' must have global linkage\n", name);
> +			return -EINVAL;
> +		} > +
> +		ret = 0;
> +		for (j = 0; j < aux->func_info_cnt; j++) {
> +			if (aux->func_info[j].type_id != i)
> +				continue;
> +			ret = aux->func_info[j].insn_off;
> +			/* Further func_info and subprog checks will also happen
> +			 * later, so assume this is the right insn_off for now.
> +			 */
> +			if (!ret) {
> +				verbose(env, "invalid exception callback insn_off in func_info: 0\n");
> +				ret = -EINVAL;
> +			}
> +		}
> +		if (!ret) {
> +			verbose(env, "exception callback type id not found in func_info\n");
> +			ret = -EINVAL;
> +		}
> +		break;
> +	}
> +	if (ret == -ENOENT)
> +		verbose(env, "exception callback '%s' could not be found in BTF\n", name);
> +	return ret;
> +}