selftests/bpf: Add kprobe session verifier test for return value

Making sure kprobe.session program can return only [0,1] values.

Signed-off-by: Jiri Olsa <[e-mail]>
Signed-off-by: Andrii Nakryiko <[e-mail]>
Acked-by: Andrii Nakryiko <[e-mail]>
Link: https://lore.kernel.org/bpf/[e-mail]

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

···
 #include "kprobe_multi_override.skel.h"
 #include "kprobe_multi_session.skel.h"
 #include "kprobe_multi_session_cookie.skel.h"
+#include "kprobe_multi_verifier.skel.h"
 #include "bpf/libbpf_internal.h"
 #include "bpf/hashmap.h"
 
···
 		test_session_skel_api();
 	if (test__start_subtest("session_cookie"))
 		test_session_cookie_skel_api();
+	RUN_TESTS(kprobe_multi_verifier);
 }

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

···
+// SPDX-License-Identifier: GPL-2.0
+#include "vmlinux.h"
+#include <bpf/bpf_helpers.h>
+#include <bpf/bpf_tracing.h>
+#include <bpf/usdt.bpf.h>
+#include "bpf_misc.h"
+
+char _license[] SEC("license") = "GPL";
+
+
+SEC("kprobe.session")
+__success
+int kprobe_session_return_0(struct pt_regs *ctx)
+{
+	return 0;
+}
+
+SEC("kprobe.session")
+__success
+int kprobe_session_return_1(struct pt_regs *ctx)
+{
+	return 1;
+}
+
+SEC("kprobe.session")
+__failure
+__msg("At program exit the register R0 has smin=2 smax=2 should have been in [0, 1]")
+int kprobe_session_return_2(struct pt_regs *ctx)
+{
+	return 2;
+}