netdev - Re: [PATCH bpf-next v4 03/10] bpf: Extend kfunc with PTR_TO_CTX, PTR_TO

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Date:   Sat, 18 Dec 2021 18:17:22 -0800
From:   Alexei Starovoitov <alexei.starovoitov@...il.com>
To:     Kumar Kartikeya Dwivedi <memxor@...il.com>
Cc:     bpf@...r.kernel.org, netdev@...r.kernel.org,
        netfilter-devel@...r.kernel.org,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andrii@...nel.org>,
        Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
        John Fastabend <john.fastabend@...il.com>,
        Maxim Mikityanskiy <maximmi@...dia.com>,
        Pablo Neira Ayuso <pablo@...filter.org>,
        Florian Westphal <fw@...len.de>,
        Jesper Dangaard Brouer <brouer@...hat.com>,
        Toke Høiland-Jørgensen <toke@...hat.com>
Subject: Re: [PATCH bpf-next v4 03/10] bpf: Extend kfunc with PTR_TO_CTX,
 PTR_TO_MEM argument support

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).