[PATCH bpf-next v5 1/9] bpf: Allow LSM programs to use bpf spin locks

[KP Singh <kpsingh@xxxxxxxxxxxx>]

From: KP Singh <kpsingh@xxxxxxxxxx>

Usage of spin locks was not allowed for tracing programs due to
insufficient preemption checks. The verifier does not currently prevent
LSM programs from using spin locks, but the helpers are not exposed
via bpf_lsm_func_proto.

Based on the discussion in [1], non-sleepable LSM programs should be
able to use bpf_spin_{lock, unlock}.

Sleepable LSM programs can be preempted which means that allowng spin
locks will need more work (disabling preemption and the verifier
ensuring that no sleepable helpers are called when a spin lock is held).

[1]: https://lore.kernel.org/bpf/20201103153132.2717326-1-kpsingh@xxxxxxxxxxxx/T/#md601a053229287659071600d3483523f752cd2fb

Acked-by: Song Liu <songliubraving@xxxxxx>
Acked-by: Martin KaFai Lau <kafai@xxxxxx>
Signed-off-by: KP Singh <kpsingh@xxxxxxxxxx>
---
 kernel/bpf/bpf_lsm.c  |  4 ++++
 kernel/bpf/verifier.c | 20 +++++++++++++++-----
 2 files changed, 19 insertions(+), 5 deletions(-)

diff --git a/kernel/bpf/bpf_lsm.c b/kernel/bpf/bpf_lsm.c
index 78ea8a7bd27f..cd8a617f2109 100644
--- a/kernel/bpf/bpf_lsm.c
+++ b/kernel/bpf/bpf_lsm.c
@@ -59,6 +59,10 @@ bpf_lsm_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog)
 		return &bpf_sk_storage_get_proto;
 	case BPF_FUNC_sk_storage_delete:
 		return &bpf_sk_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);
 	}
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 6200519582a6..f863aa84d0a2 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -9719,11 +9719,21 @@ static int check_map_prog_compatibility(struct bpf_verifier_env *env,
 		verbose(env, "trace type programs with run-time allocated hash maps are unsafe. Switch to preallocated hash maps.\n");
 	}
 
-	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;
+	if (map_value_has_spin_lock(map)) {
+		if (prog_type == BPF_PROG_TYPE_SOCKET_FILTER) {
+			verbose(env, "socket filter progs cannot use bpf_spin_lock yet\n");
+			return -EINVAL;
+		}
+
+		if (is_tracing_prog_type(prog_type)) {
+			verbose(env, "tracing progs cannot use bpf_spin_lock yet\n");
+			return -EINVAL;
+		}
+
+		if (prog->aux->sleepable) {
+			verbose(env, "sleepable progs cannot use bpf_spin_lock yet\n");
+			return -EINVAL;
+		}
 	}
 
 	if ((bpf_prog_is_dev_bound(prog->aux) || bpf_map_is_dev_bound(map)) &&
-- 
2.29.1.341.ge80a0c044ae-goog