[PATCH 2/2] selftests/bpf: Add test for bpf_override_return helper

[Jiri Olsa <jolsa@kernel.org>]

We do not actualy test the bpf_override_return helper functionality
itself at the moment, only the bpf program being able to attach it.

Adding test that override prctl syscall return value on top of
kprobe and kprobe.multi.

Signed-off-by: Jiri Olsa <jolsa@kernel.org>
---
 .../bpf/prog_tests/kprobe_multi_test.c        | 61 +++++++++++++++++++
 .../bpf/progs/kprobe_multi_override.c         | 15 +++++
 2 files changed, 76 insertions(+)

diff --git a/tools/testing/selftests/bpf/prog_tests/kprobe_multi_test.c b/tools/testing/selftests/bpf/prog_tests/kprobe_multi_test.c
index 6cfaa978bc9a..b5e5cc54b89a 100644
--- a/tools/testing/selftests/bpf/prog_tests/kprobe_multi_test.c
+++ b/tools/testing/selftests/bpf/prog_tests/kprobe_multi_test.c
@@ -1,4 +1,6 @@
 // SPDX-License-Identifier: GPL-2.0
+#include <errno.h>
+#include <sys/prctl.h>
 #include <test_progs.h>
 #include "kprobe_multi.skel.h"
 #include "trace_helpers.h"
@@ -540,6 +542,63 @@ static void test_attach_override(void)
 	kprobe_multi_override__destroy(skel);
 }
 
+/* XXX I'll move this to common place and share with
+ * SYS_NANOSLEEP_KPROBE_NAME macro on repost.
+ */
+#ifdef __x86_64__
+#define SYS_PREFIX "__x64_"
+#elif defined(__s390x__)
+#define SYS_PREFIX "__s390x_"
+#elif defined(__aarch64__)
+#define SYS_PREFIX "__arm64_"
+#elif defined(__riscv)
+#define SYS_PREFIX "__riscv_"
+#else
+#define SYS_PREFIX ""
+#endif
+
+static void test_override(void)
+{
+	struct kprobe_multi_override *skel = NULL;
+	int err;
+
+	skel = kprobe_multi_override__open_and_load();
+	if (!ASSERT_OK_PTR(skel, "kprobe_multi_empty__open_and_load"))
+		goto cleanup;
+
+	skel->bss->pid = getpid();
+
+	/* no override */
+	err = prctl(0xffff, 0);
+	ASSERT_EQ(err, -1, "err");
+
+	/* kprobe.multi override */
+	skel->links.test_override = bpf_program__attach_kprobe_multi_opts(skel->progs.test_override,
+						SYS_PREFIX "sys_prctl", NULL);
+	if (!ASSERT_OK_PTR(skel->links.test_override, "bpf_program__attach_kprobe_multi_opts")) {
+		goto cleanup;
+	}
+
+	err = prctl(0xffff, 0);
+	ASSERT_EQ(err, 123, "err");
+
+	bpf_link__destroy(skel->links.test_override);
+	skel->links.test_override = NULL;
+
+	/* kprobe override */
+	skel->links.test_kprobe_override = bpf_program__attach_kprobe(skel->progs.test_kprobe_override,
+							false, SYS_PREFIX "sys_prctl");
+	if (!ASSERT_OK_PTR(skel->links.test_kprobe_override, "bpf_program__attach_kprobe")) {
+		goto cleanup;
+	}
+
+	err = prctl(0xffff, 0);
+	ASSERT_EQ(err, 123, "err");
+
+cleanup:
+	kprobe_multi_override__destroy(skel);
+}
+
 #ifdef __x86_64__
 static void test_attach_write_ctx(void)
 {
@@ -597,6 +656,8 @@ void test_kprobe_multi_test(void)
 		test_attach_api_fails();
 	if (test__start_subtest("attach_override"))
 		test_attach_override();
+	if (test__start_subtest("override"))
+		test_override();
 	if (test__start_subtest("session"))
 		test_session_skel_api();
 	if (test__start_subtest("session_cookie"))
diff --git a/tools/testing/selftests/bpf/progs/kprobe_multi_override.c b/tools/testing/selftests/bpf/progs/kprobe_multi_override.c
index 28f8487c9059..14f39fa6d515 100644
--- a/tools/testing/selftests/bpf/progs/kprobe_multi_override.c
+++ b/tools/testing/selftests/bpf/progs/kprobe_multi_override.c
@@ -5,9 +5,24 @@
 
 char _license[] SEC("license") = "GPL";
 
+int pid = 0;
+
 SEC("kprobe.multi")
 int test_override(struct pt_regs *ctx)
 {
+	if (bpf_get_current_pid_tgid() >> 32 != pid)
+		return 0;
+
+	bpf_override_return(ctx, 123);
+	return 0;
+}
+
+SEC("kprobe")
+int test_kprobe_override(struct pt_regs *ctx)
+{
+	if (bpf_get_current_pid_tgid() >> 32 != pid)
+		return 0;
+
 	bpf_override_return(ctx, 123);
 	return 0;
 }
-- 
2.51.1