selftests/bpf: Add uprobe_regs_equal test

Changing uretprobe_regs_trigger to allow the test for both
uprobe and uretprobe and renaming it to uprobe_regs_equal.

We check that both uprobe and uretprobe probes (bpf programs)
see expected registers with few exceptions.

Signed-off-by: Jiri Olsa <[e-mail]>
Signed-off-by: Peter Zijlstra (Intel) <[e-mail]>
Acked-by: Andrii Nakryiko <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]

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

···
 
 #pragma GCC diagnostic ignored "-Wattributes"
 
-__naked unsigned long uretprobe_regs_trigger(void)
+__attribute__((aligned(16)))
+__nocf_check __weak __naked unsigned long uprobe_regs_trigger(void)
 {
 	asm volatile (
+		".byte 0x0f, 0x1f, 0x44, 0x00, 0x00\n" /* nop5 */
 		"movq $0xdeadbeef, %rax\n"
 		"ret\n"
 	);
 }
 
-__naked void uretprobe_regs(struct pt_regs *before, struct pt_regs *after)
+__naked void uprobe_regs(struct pt_regs *before, struct pt_regs *after)
 {
 	asm volatile (
 		"movq %r15,   0(%rdi)\n"
···
 		"movq   $0, 120(%rdi)\n" /* orig_rax */
 		"movq   $0, 128(%rdi)\n" /* rip      */
 		"movq   $0, 136(%rdi)\n" /* cs       */
+		"pushq %rax\n"
 		"pushf\n"
 		"pop %rax\n"
 		"movq %rax, 144(%rdi)\n" /* eflags   */
+		"pop %rax\n"
 		"movq %rsp, 152(%rdi)\n" /* rsp      */
 		"movq   $0, 160(%rdi)\n" /* ss       */
 
 		/* save 2nd argument */
 		"pushq %rsi\n"
-		"call uretprobe_regs_trigger\n"
+		"call uprobe_regs_trigger\n"
 
 		/* save  return value and load 2nd argument pointer to rax */
 		"pushq %rax\n"
···
 );
 }
 
-static void test_uretprobe_regs_equal(void)
+static void test_uprobe_regs_equal(bool retprobe)
 {
+	LIBBPF_OPTS(bpf_uprobe_opts, opts,
+		.retprobe = retprobe,
+	);
 	struct uprobe_syscall *skel = NULL;
 	struct pt_regs before = {}, after = {};
 	unsigned long *pb = (unsigned long *) &before;
 	unsigned long *pa = (unsigned long *) &after;
 	unsigned long *pp;
+	unsigned long offset;
 	unsigned int i, cnt;
-	int err;
+
+	offset = get_uprobe_offset(&uprobe_regs_trigger);
+	if (!ASSERT_GE(offset, 0, "get_uprobe_offset"))
+		return;
 
 	skel = uprobe_syscall__open_and_load();
 	if (!ASSERT_OK_PTR(skel, "uprobe_syscall__open_and_load"))
 		goto cleanup;
 
-	err = uprobe_syscall__attach(skel);
-	if (!ASSERT_OK(err, "uprobe_syscall__attach"))
+	skel->links.probe = bpf_program__attach_uprobe_opts(skel->progs.probe,
+				0, "/proc/self/exe", offset, &opts);
+	if (!ASSERT_OK_PTR(skel->links.probe, "bpf_program__attach_uprobe_opts"))
 		goto cleanup;
 
-	uretprobe_regs(&before, &after);
+	/* make sure uprobe gets optimized */
+	if (!retprobe)
+		uprobe_regs_trigger();
+
+	uprobe_regs(&before, &after);
 
 	pp = (unsigned long *) &skel->bss->regs;
 	cnt = sizeof(before)/sizeof(*pb);
···
 		unsigned int offset = i * sizeof(unsigned long);
 
 		/*
-		 * Check register before and after uretprobe_regs_trigger call
+		 * Check register before and after uprobe_regs_trigger call
 		 * that triggers the uretprobe.
 		 */
 		switch (offset) {
···
 
 		/*
 		 * Check register seen from bpf program and register after
-		 * uretprobe_regs_trigger call
+		 * uprobe_regs_trigger call (with rax exception, check below).
 		 */
 		switch (offset) {
 		/*
···
 		case offsetof(struct pt_regs, rsp):
 		case offsetof(struct pt_regs, ss):
 			break;
+		/*
+		 * uprobe does not see return value in rax, it needs to see the
+		 * original (before) rax value
+		 */
+		case offsetof(struct pt_regs, rax):
+			if (!retprobe) {
+				ASSERT_EQ(pp[i], pb[i], "uprobe rax prog-before value check");
+				break;
+			}
 		default:
 			if (!ASSERT_EQ(pp[i], pa[i], "register prog-after value check"))
 				fprintf(stdout, "failed register offset %u\n", offset);
···
 	unsigned long cnt = sizeof(before)/sizeof(*pb);
 	unsigned int i, err, offset;
 
-	offset = get_uprobe_offset(uretprobe_regs_trigger);
+	offset = get_uprobe_offset(uprobe_regs_trigger);
 
 	err = write_bpf_testmod_uprobe(offset);
 	if (!ASSERT_OK(err, "register_uprobe"))
 		return;
 
-	uretprobe_regs(&before, &after);
+	uprobe_regs(&before, &after);
 
 	err = write_bpf_testmod_uprobe(0);
 	if (!ASSERT_OK(err, "unregister_uprobe"))
···
 	/* Run all the tests with shadow stack in place. */
 	shstk_is_enabled = true;
 
-	test_uretprobe_regs_equal();
+	test_uprobe_regs_equal(false);
+	test_uprobe_regs_equal(true);
 	test_uretprobe_regs_change();
 	test_uretprobe_syscall_call();
 
···
 static void __test_uprobe_syscall(void)
 {
 	if (test__start_subtest("uretprobe_regs_equal"))
-		test_uretprobe_regs_equal();
+		test_uprobe_regs_equal(true);
 	if (test__start_subtest("uretprobe_regs_change"))
 		test_uretprobe_regs_change();
 	if (test__start_subtest("uretprobe_syscall_call"))
···
 		test_uprobe_race();
 	if (test__start_subtest("uprobe_sigill"))
 		test_uprobe_sigill();
+	if (test__start_subtest("uprobe_regs_equal"))
+		test_uprobe_regs_equal(false);
 }
 #else
 static void __test_uprobe_syscall(void)

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

···
 
 char _license[] SEC("license") = "GPL";
 
-SEC("uretprobe//proc/self/exe:uretprobe_regs_trigger")
-int uretprobe(struct pt_regs *ctx)
+SEC("uprobe")
+int probe(struct pt_regs *ctx)
 {
 	__builtin_memcpy(&regs, ctx, sizeof(regs));
 	return 0;