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Date:   Tue, 03 Nov 2020 22:51:30 -0800
From:   John Fastabend <john.fastabend@gmail.com>
To:     Alexei Starovoitov <alexei.starovoitov@gmail.com>,
        KP Singh <kpsingh@chromium.org>
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        bpf <bpf@vger.kernel.org>, Alexei Starovoitov <ast@kernel.org>,
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        Martin KaFai Lau <kafai@fb.com>,
        Song Liu <songliubraving@fb.com>, Paul Turner <pjt@google.com>,
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Subject: Re: [PATCH bpf-next v2 7/8] bpf: Add tests for task_local_storage
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Alexei Starovoitov wrote:
> On Tue, Nov 3, 2020 at 5:55 PM KP Singh <kpsingh@chromium.org> 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?