selftests/bpf: Add kprobe session test

Adding kprobe session test and testing that the entry program
return value controls execution of the return probe program.
Signed-off-by: Jiri Olsa <jolsa@kernel.org>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20240430112830.1184228-7-jolsa@kernel.org

tools/testing/selftests/bpf/bpf_kfuncs.h

@@ -75,4 +75,6 @@ extern void bpf_key_put(struct bpf_key *key) __ksym;
 extern int bpf_verify_pkcs7_signature(struct bpf_dynptr *data_ptr,
 				      struct bpf_dynptr *sig_ptr,
 				      struct bpf_key *trusted_keyring) __ksym;
+
+extern bool bpf_session_is_return(void) __ksym __weak;
 #endif

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

@@ -4,6 +4,7 @@
 #include "trace_helpers.h"
 #include "kprobe_multi_empty.skel.h"
 #include "kprobe_multi_override.skel.h"
+#include "kprobe_multi_session.skel.h"
 #include "bpf/libbpf_internal.h"
 #include "bpf/hashmap.h"
 
@@ -326,6 +327,42 @@ static void test_attach_api_fails(void)
 	kprobe_multi__destroy(skel);
 }
 
+static void test_session_skel_api(void)
+{
+	struct kprobe_multi_session *skel = NULL;
+	LIBBPF_OPTS(bpf_kprobe_multi_opts, opts);
+	LIBBPF_OPTS(bpf_test_run_opts, topts);
+	struct bpf_link *link = NULL;
+	int i, err, prog_fd;
+
+	skel = kprobe_multi_session__open_and_load();
+	if (!ASSERT_OK_PTR(skel, "kprobe_multi_session__open_and_load"))
+		return;
+
+	skel->bss->pid = getpid();
+
+	err = kprobe_multi_session__attach(skel);
+	if (!ASSERT_OK(err, " kprobe_multi_session__attach"))
+		goto cleanup;
+
+	prog_fd = bpf_program__fd(skel->progs.trigger);
+	err = bpf_prog_test_run_opts(prog_fd, &topts);
+	ASSERT_OK(err, "test_run");
+	ASSERT_EQ(topts.retval, 0, "test_run");
+
+	/* bpf_fentry_test1-4 trigger return probe, result is 2 */
+	for (i = 0; i < 4; i++)
+		ASSERT_EQ(skel->bss->kprobe_session_result[i], 2, "kprobe_session_result");
+
+	/* bpf_fentry_test5-8 trigger only entry probe, result is 1 */
+	for (i = 4; i < 8; i++)
+		ASSERT_EQ(skel->bss->kprobe_session_result[i], 1, "kprobe_session_result");
+
+cleanup:
+	bpf_link__destroy(link);
+	kprobe_multi_session__destroy(skel);
+}
+
 static size_t symbol_hash(long key, void *ctx __maybe_unused)
 {
 	return str_hash((const char *) key);
@@ -690,4 +727,6 @@ void test_kprobe_multi_test(void)
 		test_attach_api_fails();
 	if (test__start_subtest("attach_override"))
 		test_attach_override();
+	if (test__start_subtest("session"))
+		test_session_skel_api();
 }

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

+// SPDX-License-Identifier: GPL-2.0
+#include <linux/bpf.h>
+#include <bpf/bpf_helpers.h>
+#include <bpf/bpf_tracing.h>
+#include <stdbool.h>
+#include "bpf_kfuncs.h"
+
+#define ARRAY_SIZE(x) (int)(sizeof(x) / sizeof((x)[0]))
+
+char _license[] SEC("license") = "GPL";
+
+extern const void bpf_fentry_test1 __ksym;
+extern const void bpf_fentry_test2 __ksym;
+extern const void bpf_fentry_test3 __ksym;
+extern const void bpf_fentry_test4 __ksym;
+extern const void bpf_fentry_test5 __ksym;
+extern const void bpf_fentry_test6 __ksym;
+extern const void bpf_fentry_test7 __ksym;
+extern const void bpf_fentry_test8 __ksym;
+
+int pid = 0;
+
+__u64 kprobe_session_result[8];
+
+static int session_check(void *ctx)
+{
+	unsigned int i;
+	__u64 addr;
+	const void *kfuncs[] = {
+		&bpf_fentry_test1,
+		&bpf_fentry_test2,
+		&bpf_fentry_test3,
+		&bpf_fentry_test4,
+		&bpf_fentry_test5,
+		&bpf_fentry_test6,
+		&bpf_fentry_test7,
+		&bpf_fentry_test8,
+	};
+
+	if (bpf_get_current_pid_tgid() >> 32 != pid)
+		return 1;
+
+	addr = bpf_get_func_ip(ctx);
+
+	for (i = 0; i < ARRAY_SIZE(kfuncs); i++) {
+		if (kfuncs[i] == (void *) addr) {
+			kprobe_session_result[i]++;
+			break;
+		}
+	}
+
+	/*
+	 * Force probes for function bpf_fentry_test[5-8] not to
+	 * install and execute the return probe
+	 */
+	if (((const void *) addr == &bpf_fentry_test5) ||
+	    ((const void *) addr == &bpf_fentry_test6) ||
+	    ((const void *) addr == &bpf_fentry_test7) ||
+	    ((const void *) addr == &bpf_fentry_test8))
+		return 1;
+
+	return 0;
+}
+
+/*
+ * No tests in here, just to trigger 'bpf_fentry_test*'
+ * through tracing test_run
+ */
+SEC("fentry/bpf_modify_return_test")
+int BPF_PROG(trigger)
+{
+	return 0;
+}
+
+SEC("kprobe.session/bpf_fentry_test*")
+int test_kprobe(struct pt_regs *ctx)
+{
+	return session_check(ctx);
+}