Alexei Starovoitov wrote:
> On Tue, Nov 3, 2020 at 5:55 PM KP Singh <kpsingh@xxxxxxxxxxxx> wrote:
> >
> > [...]
> >
> > > >
> > > > I saw the docs mention that these are not exposed to tracing programs due to
> > > > insufficient preemption checks. Do you think it would be okay to allow them
> > > > for LSM programs?
> > >
> > > hmm. Isn't it allowed already?
> > > The verifier does:
> > > if ((is_tracing_prog_type(prog_type) ||
> > > prog_type == BPF_PROG_TYPE_SOCKET_FILTER) &&
> > > map_value_has_spin_lock(map)) {
> > > verbose(env, "tracing progs cannot use bpf_spin_lock yet\n");
> > > return -EINVAL;
> > > }
> > >
> > > BPF_PROG_TYPE_LSM is not in this list.
> >
> > The verifier does not have any problem, it's just that the helpers are not
> > exposed to LSM programs via bpf_lsm_func_proto.
> >
> > So all we need is:
> >
> > diff --git a/kernel/bpf/bpf_lsm.c b/kernel/bpf/bpf_lsm.c
> > index 61f8cc52fd5b..93383df2140b 100644
> > --- a/kernel/bpf/bpf_lsm.c
> > +++ b/kernel/bpf/bpf_lsm.c
> > @@ -63,6 +63,10 @@ bpf_lsm_func_proto(enum bpf_func_id func_id, const
> > struct bpf_prog *prog)
> > return &bpf_task_storage_get_proto;
> > case BPF_FUNC_task_storage_delete:
> > return &bpf_task_storage_delete_proto;
> > + case BPF_FUNC_spin_lock:
> > + return &bpf_spin_lock_proto;
> > + case BPF_FUNC_spin_unlock:
> > + return &bpf_spin_unlock_proto;
>
> Ahh. Yes. That should do it. Right now I don't see concerns with safety
> of the bpf_spin_lock in bpf_lsm progs.
What about sleepable lsm hooks? Normally we wouldn't expect to sleep with
a spinlock held. Should we have a check to ensure programs bpf_spin_lock
are not also sleepable?
