linux-kernel - Re: [PATCH bpf-next v2 7/8] bpf: Add tests for task_local

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Date:   Tue, 3 Nov 2020 17:57:32 -0800
From:   Alexei Starovoitov <alexei.starovoitov@...il.com>
To:     KP Singh <kpsingh@...omium.org>
Cc:     open list <linux-kernel@...r.kernel.org>,
        bpf <bpf@...r.kernel.org>, Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>, Paul Turner <pjt@...gle.com>,
        Jann Horn <jannh@...gle.com>, Hao Luo <haoluo@...gle.com>
Subject: Re: [PATCH bpf-next v2 7/8] bpf: Add tests for task_local_storage

On Tue, Nov 3, 2020 at 5:55 PM KP Singh <kpsingh@...omium.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.