Re: [RFC PATCH v9 05/11] bpf: net_sched: Support implementation of Qdisc_ops in bpf

[Amery Hung <ameryhung@gmail.com>]

On Thu, Jul 25, 2024 at 2:25 PM Martin KaFai Lau <martin.lau@linux.dev> wrote:
>
> On 7/14/24 10:51 AM, Amery Hung wrote:
> > +static const struct bpf_func_proto *
> > +bpf_qdisc_get_func_proto(enum bpf_func_id func_id,
> > +                      const struct bpf_prog *prog)
> > +{
> > +     switch (func_id) {
>
> Instead of an empty switch, it should be useful to provide the skb->data related
> helper. It can start with read only dynptr first, the BPF_FUNC_dynptr_read
> helper here.
>
> Also, the kfuncs: bpf_dynptr_slice and bpf_dynptr_from_skb_rdonly.
>

I will add the helper and kfuncs and try them out.

> > +     default:
> > +             return bpf_base_func_proto(func_id, prog);
>
> [ ... ]
>
> > +     }
> > +}
> > +
> > +BTF_ID_LIST_SINGLE(bpf_sk_buff_ids, struct, sk_buff)
> > +BTF_ID_LIST_SINGLE(bpf_sk_buff_ptr_ids, struct, bpf_sk_buff_ptr)
> > +
> > +static bool bpf_qdisc_is_valid_access(int off, int size,
> > +                                   enum bpf_access_type type,
> > +                                   const struct bpf_prog *prog,
> > +                                   struct bpf_insn_access_aux *info)
> > +{
> > +     struct btf *btf = prog->aux->attach_btf;
> > +     u32 arg;
> > +
> > +     arg = get_ctx_arg_idx(btf, prog->aux->attach_func_proto, off);
> > +     if (!strcmp(prog->aux->attach_func_name, "enqueue")) {
> > +             if (arg == 2) {
> > +                     info->reg_type = PTR_TO_BTF_ID | PTR_TRUSTED;
> > +                     info->btf = btf;
> > +                     info->btf_id = bpf_sk_buff_ptr_ids[0];
> > +                     return true;
>
> This will allow type == BPF_WRITE to ctx which should be rejected. The below
> bpf_tracing_btf_ctx_access() could have rejected it.
>

Right. I will check the access type of the "to_free" argument in .enqueue.

> > +             }
> > +     }
> > +
> > +     return bpf_tracing_btf_ctx_access(off, size, type, prog, info);
> > +}
> > +
>
> [ ... ]
>
> > +
> > +static bool is_unsupported(u32 member_offset)
> > +{
> > +     unsigned int i;
> > +
> > +     for (i = 0; i < ARRAY_SIZE(unsupported_ops); i++) {
> > +             if (member_offset == unsupported_ops[i])
> > +                     return true;
> > +     }
> > +
> > +     return false;
> > +}
> > +
> > +static int bpf_qdisc_check_member(const struct btf_type *t,
> > +                               const struct btf_member *member,
> > +                               const struct bpf_prog *prog)
> > +{
> > +     if (is_unsupported(__btf_member_bit_offset(t, member) / 8))
>
> Note that the ".check_member" and the "is_unsupported" can be removed as you
> also noticed on the recent unsupported ops cleanup patches.

Thanks for looping me in. I removed them when testing the series.

>
> > +             return -ENOTSUPP;
> > +     return 0;
> > +}
>
> [ ... ]
>
> > +static struct Qdisc_ops __bpf_ops_qdisc_ops = {
> > +     .enqueue = Qdisc_ops__enqueue,
> > +     .dequeue = Qdisc_ops__dequeue,
> > +     .peek = Qdisc_ops__peek,
> > +     .init = Qdisc_ops__init,
> > +     .reset = Qdisc_ops__reset,
> > +     .destroy = Qdisc_ops__destroy,
> > +     .change = Qdisc_ops__change,
> > +     .attach = Qdisc_ops__attach,
> > +     .change_tx_queue_len = Qdisc_ops__change_tx_queue_len,
> > +     .change_real_num_tx = Qdisc_ops__change_real_num_tx,
> > +     .dump = Qdisc_ops__dump,
> > +     .dump_stats = Qdisc_ops__dump_stats,
>
> Similar to the above is_unsupported comment. The unsupported ops should be
> removed from the cfi_stubs.
>
> > +     .ingress_block_set = Qdisc_ops__ingress_block_set,
> > +     .egress_block_set = Qdisc_ops__egress_block_set,
> > +     .ingress_block_get = Qdisc_ops__ingress_block_get,
> > +     .egress_block_get = Qdisc_ops__egress_block_get,
> > +};
> > +
> > +static struct bpf_struct_ops bpf_Qdisc_ops = {
> > +     .verifier_ops = &bpf_qdisc_verifier_ops,
> > +     .reg = bpf_qdisc_reg,
> > +     .unreg = bpf_qdisc_unreg,
> > +     .check_member = bpf_qdisc_check_member,
> > +     .init_member = bpf_qdisc_init_member,
> > +     .init = bpf_qdisc_init,
> > +     .validate = bpf_qdisc_validate,
>
> ".validate" is optional. The empty "bpf_qdisc_validate" can be removed.
>

Got it.


> > +     .name = "Qdisc_ops",
> > +     .cfi_stubs = &__bpf_ops_qdisc_ops,
> > +     .owner = THIS_MODULE,
> > +};
>
>