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

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

On Sat, Dec 18, 2021 at 8:38 PM Kumar Kartikeya Dwivedi
<memxor@gmail.com> wrote:
>
> On Sun, Dec 19, 2021 at 09:24:37AM IST, Alexei Starovoitov wrote:
> > On Sat, Dec 18, 2021 at 7:01 PM Kumar Kartikeya Dwivedi
> > <memxor@gmail.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".
> >
>
> Nice idea, I think this is better than what I am doing (it also prevents
> constant researching into the list).
>
> But IIUC I think this btf_ids array needs to go into struct btf instead,
> since if module is compiled as built-in, we will not have any struct module for
> it.
>
> Then we can concatenate all sets of same type (check/acquire/release etc.) and
> sort them to directly search using a single btf_id_set_contains call, the code
> becomes same for btf_vmlinux or module btf. struct module is not needed anymore.
>
> WDYT?

You mean that btf_parse_module() will do this?
That would work for vmlinux's BTF too then?
Makes sense to me!