netdev - Re: [PATCH bpf-next v4 05/10] bpf: Add reference tracking support to kfunc

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Date:   Sat, 18 Dec 2021 19:54:37 -0800
From:   Alexei Starovoitov <alexei.starovoitov@...il.com>
To:     Kumar Kartikeya Dwivedi <memxor@...il.com>
Cc:     bpf <bpf@...r.kernel.org>,
        Network Development <netdev@...r.kernel.org>,
        netfilter-devel <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 05/10] bpf: Add reference tracking support to kfunc

On Sat, Dec 18, 2021 at 7:01 PM Kumar Kartikeya Dwivedi
<memxor@...il.com> wrote:
>
> On Sun, Dec 19, 2021 at 07:52:48AM IST, Alexei Starovoitov wrote:
> > On Fri, Dec 17, 2021 at 07:20:26AM +0530, Kumar Kartikeya Dwivedi wrote:
> > >
> > > diff --git a/include/linux/bpf.h b/include/linux/bpf.h
> > > index 965fffaf0308..015cb633838b 100644
> > > --- a/include/linux/bpf.h
> > > +++ b/include/linux/bpf.h
> > > @@ -521,6 +521,9 @@ struct bpf_verifier_ops {
> > >                              enum bpf_access_type atype,
> > >                              u32 *next_btf_id);
> > >     bool (*check_kfunc_call)(u32 kfunc_btf_id, struct module *owner);
> > > +   bool (*is_acquire_kfunc)(u32 kfunc_btf_id, struct module *owner);
> > > +   bool (*is_release_kfunc)(u32 kfunc_btf_id, struct module *owner);
> > > +   bool (*is_kfunc_ret_type_null)(u32 kfunc_btf_id, struct module *owner);
> >
> > Same feedback as before...
> >
> > Those callbacks are not necessary.
> > The existing check_kfunc_call() is just as inconvenient.
> > When module's BTF comes in could you add it to mod's info instead of
> > introducing callbacks for every kind of data the module has.
> > Those callbacks don't server any purpose other than passing the particular
> > data set back. The verifier side should access those data sets directly.
>
> Ok, interesting idea. So these then go into the ".modinfo" section?

It doesn't need to be a special section.
The btf_module_notify() parses BTF.
At the same time it can add a kfunc whitelist to "struct module".
The btf_ids[ACQUIRE/RELEASE][] arrays will be a part of
the "struct module" too.
If we can do a btf name convention then this job can be
performed generically by btf_module_notify().
Otherwise __init of the module can populate arrays in "struct module".

> I think then
> we can also drop the check_kfunc_call callback?

Right. Would be great to remove that callback too.