Re: [PATCH bpf-next v4 03/10] bpf: Extend kfunc with PTR_TO_CTX, PTR_TO_MEM argument support

[Alexei Starovoitov <alexei.starovoitov@gmail.com>]

On Fri, Dec 17, 2021 at 07:20:24AM +0530, Kumar Kartikeya Dwivedi wrote:
>  
> +/* Returns true if struct is composed of scalars, 4 levels of nesting allowed */
> +static bool __btf_type_is_scalar_struct(struct bpf_verifier_log *log,
> +					const struct btf *btf,
> +					const struct btf_type *t, int rec)
> +{
> +	const struct btf_type *member_type;
> +	const struct btf_member *member;
> +	u16 i;
> +
> +	if (rec == 4) {
> +		bpf_log(log, "max struct nesting depth 4 exceeded\n");
> +		return false;
> +	}

As Matteo found out that saves stack with gcc only,
so I moved this check few lines below, just before recursive call.

> +			if (is_kfunc) {
> +				/* Permit pointer to mem, but only when argument
> +				 * type is pointer to scalar, or struct composed
> +				 * (recursively) of scalars.
> +				 */
> +				if (!btf_type_is_scalar(ref_t) && !__btf_type_is_scalar_struct(log, btf, ref_t, 0)) {

... and reformatted this line to fit screen width.

... and applied.

Please add individual selftest for this feature
(not tied into refcnted kfuncs and CT).