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From:   KP Singh <kpsingh@chromium.org>
Date:   Wed, 4 Nov 2020 02:55:25 +0100
Message-ID: <CACYkzJ6uc4fbRMNmj3kFeSu=V2JqWruJLFjMnPet_HXW-EdRng@mail.gmail.com>
Subject: Re: [PATCH bpf-next v2 7/8] bpf: Add tests for task_local_storage
To:     Alexei Starovoitov <alexei.starovoitov@gmail.com>
Cc:     open list <linux-kernel@vger.kernel.org>,
        bpf <bpf@vger.kernel.org>, Alexei Starovoitov <ast@kernel.org>,
        Daniel Borkmann <daniel@iogearbox.net>,
        Martin KaFai Lau <kafai@fb.com>,
        Song Liu <songliubraving@fb.com>, Paul Turner <pjt@google.com>,
        Jann Horn <jannh@google.com>, Hao Luo <haoluo@google.com>
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[...]

> >
> > 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;
        default:
                return tracing_prog_func_proto(func_id, prog);
        }