[PATCH bpf-next 8/8] selftests/bpf: Add a test to verify session-kfunc compatibility enforcement

[Leon Hwang <leon.hwang@linux.dev>]

Add prog_array coverage for tracing programs that differ in
bpf_session_cookie() / bpf_session_is_return() usage.

The test verifies one-way enforcement: !call_session_* programs
cannot tail-call call_session_* programs.

Assisted-by: Codex:gpt-5.3-codex
Signed-off-by: Leon Hwang <leon.hwang@linux.dev>
---
 .../selftests/bpf/prog_tests/fsession_test.c  | 47 +++++++++++++++++++
 .../selftests/bpf/progs/fsession_test.c       |  6 +++
 2 files changed, 53 insertions(+)

diff --git a/tools/testing/selftests/bpf/prog_tests/fsession_test.c b/tools/testing/selftests/bpf/prog_tests/fsession_test.c
index a299aeb8cc2e..304986544a8d 100644
--- a/tools/testing/selftests/bpf/prog_tests/fsession_test.c
+++ b/tools/testing/selftests/bpf/prog_tests/fsession_test.c
@@ -129,6 +129,51 @@ static void test_fsession_cookie(void)
 	fsession_test__destroy(skel);
 }
 
+static void test_fsession_prog_array_session_kfunc_compat(void)
+{
+	struct fsession_test *skel = NULL;
+	__u32 key = 0, session_kfunc_prog_fd, no_session_kfunc_prog_fd;
+	int map_fd = -1, err;
+
+	skel = fsession_test__open();
+	if (!ASSERT_OK_PTR(skel, "fsession_test__open"))
+		goto cleanup;
+
+	err = fsession_test__load(skel);
+	if (err == -EOPNOTSUPP) {
+		test__skip();
+		goto cleanup;
+	}
+	if (!ASSERT_OK(err, "fsession_test__load"))
+		goto cleanup;
+
+	session_kfunc_prog_fd = bpf_program__fd(skel->progs.test9);
+	no_session_kfunc_prog_fd = bpf_program__fd(skel->progs.test12);
+	if (!ASSERT_GE(session_kfunc_prog_fd, 0, "session_kfunc_prog_fd"))
+		goto cleanup;
+	if (!ASSERT_GE(no_session_kfunc_prog_fd, 0, "no_session_kfunc_prog_fd"))
+		goto cleanup;
+
+	map_fd = bpf_map_create(BPF_MAP_TYPE_PROG_ARRAY, NULL, sizeof(key),
+				sizeof(__u32), 1, NULL);
+	if (!ASSERT_GE(map_fd, 0, "bpf_map_create"))
+		goto cleanup;
+
+	err = bpf_map_update_elem(map_fd, &key, &no_session_kfunc_prog_fd, BPF_ANY);
+	if (!ASSERT_OK(err, "bpf_map_update_elem success"))
+		goto cleanup;
+
+	err = bpf_map_update_elem(map_fd, &key, &session_kfunc_prog_fd, BPF_ANY);
+	if (!ASSERT_ERR(err, "bpf_map_update_elem failure"))
+		goto cleanup;
+	ASSERT_EQ(errno, EINVAL, "bpf_map_update_elem errno");
+
+cleanup:
+	if (map_fd >= 0)
+		close(map_fd);
+	fsession_test__destroy(skel);
+}
+
 void test_fsession_test(void)
 {
 	if (test__start_subtest("fsession_test"))
@@ -137,4 +182,6 @@ void test_fsession_test(void)
 		test_fsession_reattach();
 	if (test__start_subtest("fsession_cookie"))
 		test_fsession_cookie();
+	if (test__start_subtest("fsession_prog_array_session_kfunc_compat"))
+		test_fsession_prog_array_session_kfunc_compat();
 }
diff --git a/tools/testing/selftests/bpf/progs/fsession_test.c b/tools/testing/selftests/bpf/progs/fsession_test.c
index 86e8a2fe467e..1e6be28bcc3d 100644
--- a/tools/testing/selftests/bpf/progs/fsession_test.c
+++ b/tools/testing/selftests/bpf/progs/fsession_test.c
@@ -177,3 +177,9 @@ int BPF_PROG(test11, int a)
 	test11_result = a == 1;
 	return 0;
 }
+
+SEC("fsession/bpf_fentry_test1")
+int BPF_PROG(test12, int a, int ret)
+{
+	return 0;
+}
-- 
2.52.0