selftests/bpf: Add selftest for attaching tracing programs to functions in deny list

The result:

 $ tools/testing/selftests/bpf/test_progs -t tracing_failure/tracing_deny
 torvalds#468/3   tracing_failure/tracing_deny:OK
 torvalds#468     tracing_failure:OK
 Summary: 1/1 PASSED, 0 SKIPPED, 0 FAILED

Signed-off-by: KaFai Wan <[email protected]>
Acked-by: Yonghong Song <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Alexei Starovoitov <[email protected]>

Author: mannkafai

tools/testing/selftests/bpf/prog_tests/tracing_failure.c

@@ -28,10 +28,43 @@ static void test_bpf_spin_lock(bool is_spin_lock)
 	tracing_failure__destroy(skel);
 }
 
+static void test_tracing_deny(void)
+{
+	struct tracing_failure *skel;
+	char log_buf[256];
+	int btf_id, err;
+
+	/* __rcu_read_lock depends on CONFIG_PREEMPT_RCU */
+	btf_id = libbpf_find_vmlinux_btf_id("__rcu_read_lock", BPF_TRACE_FENTRY);
+	if (btf_id <= 0) {
+		test__skip();
+		return;
+	}
+
+	skel = tracing_failure__open();
+	if (!ASSERT_OK_PTR(skel, "tracing_failure__open"))
+		return;
+
+	bpf_program__set_autoload(skel->progs.tracing_deny, true);
+	bpf_program__set_log_buf(skel->progs.tracing_deny, log_buf, sizeof(log_buf));
+
+	err = tracing_failure__load(skel);
+	if (!ASSERT_ERR(err, "tracing_failure__load"))
+		goto out;
+
+	ASSERT_HAS_SUBSTR(log_buf,
+			  "Attaching tracing programs to function '__rcu_read_lock' is rejected.",
+			  "log_buf");
+out:
+	tracing_failure__destroy(skel);
+}
+
 void test_tracing_failure(void)
 {
 	if (test__start_subtest("bpf_spin_lock"))
 		test_bpf_spin_lock(true);
 	if (test__start_subtest("bpf_spin_unlock"))
 		test_bpf_spin_lock(false);
+	if (test__start_subtest("tracing_deny"))
+		test_tracing_deny();
 }

tools/testing/selftests/bpf/progs/tracing_failure.c

@@ -18,3 +18,9 @@ int BPF_PROG(test_spin_unlock, struct bpf_spin_lock *lock)
 {
 	return 0;
 }
+
+SEC("?fentry/__rcu_read_lock")
+int BPF_PROG(tracing_deny)
+{
+	return 0;
+}