selftests/bpf: Add a test to confirm PT_REGS_PARM4_SYSCALL

Add a selftest to verify the behavior of PT_REGS_xxx
and the CORE variant.
Signed-off-by: Kenta Tada <Kenta.Tada@sony.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20220124141622.4378-4-Kenta.Tada@sony.com

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

+// SPDX-License-Identifier: GPL-2.0
+/* Copyright 2022 Sony Group Corporation */
+#include <sys/prctl.h>
+#include <test_progs.h>
+#include "bpf_syscall_macro.skel.h"
+
+void test_bpf_syscall_macro(void)
+{
+	struct bpf_syscall_macro *skel = NULL;
+	int err;
+	int exp_arg1 = 1001;
+	unsigned long exp_arg2 = 12;
+	unsigned long exp_arg3 = 13;
+	unsigned long exp_arg4 = 14;
+	unsigned long exp_arg5 = 15;
+
+	/* check whether it can open program */
+	skel = bpf_syscall_macro__open();
+	if (!ASSERT_OK_PTR(skel, "bpf_syscall_macro__open"))
+		return;
+
+	skel->rodata->filter_pid = getpid();
+
+	/* check whether it can load program */
+	err = bpf_syscall_macro__load(skel);
+	if (!ASSERT_OK(err, "bpf_syscall_macro__load"))
+		goto cleanup;
+
+	/* check whether it can attach kprobe */
+	err = bpf_syscall_macro__attach(skel);
+	if (!ASSERT_OK(err, "bpf_syscall_macro__attach"))
+		goto cleanup;
+
+	/* check whether args of syscall are copied correctly */
+	prctl(exp_arg1, exp_arg2, exp_arg3, exp_arg4, exp_arg5);
+	ASSERT_EQ(skel->bss->arg1, exp_arg1, "syscall_arg1");
+	ASSERT_EQ(skel->bss->arg2, exp_arg2, "syscall_arg2");
+	ASSERT_EQ(skel->bss->arg3, exp_arg3, "syscall_arg3");
+	/* it cannot copy arg4 when uses PT_REGS_PARM4 on x86_64 */
+#ifdef __x86_64__
+	ASSERT_NEQ(skel->bss->arg4_cx, exp_arg4, "syscall_arg4_from_cx");
+#else
+	ASSERT_EQ(skel->bss->arg4_cx, exp_arg4, "syscall_arg4_from_cx");
+#endif
+	ASSERT_EQ(skel->bss->arg4, exp_arg4, "syscall_arg4");
+	ASSERT_EQ(skel->bss->arg5, exp_arg5, "syscall_arg5");
+
+	/* check whether args of syscall are copied correctly for CORE variants */
+	ASSERT_EQ(skel->bss->arg1_core, exp_arg1, "syscall_arg1_core_variant");
+	ASSERT_EQ(skel->bss->arg2_core, exp_arg2, "syscall_arg2_core_variant");
+	ASSERT_EQ(skel->bss->arg3_core, exp_arg3, "syscall_arg3_core_variant");
+	/* it cannot copy arg4 when uses PT_REGS_PARM4_CORE on x86_64 */
+#ifdef __x86_64__
+	ASSERT_NEQ(skel->bss->arg4_core_cx, exp_arg4, "syscall_arg4_from_cx_core_variant");
+#else
+	ASSERT_EQ(skel->bss->arg4_core_cx, exp_arg4, "syscall_arg4_from_cx_core_variant");
+#endif
+	ASSERT_EQ(skel->bss->arg4_core, exp_arg4, "syscall_arg4_core_variant");
+	ASSERT_EQ(skel->bss->arg5_core, exp_arg5, "syscall_arg5_core_variant");
+
+cleanup:
+	bpf_syscall_macro__destroy(skel);
+}

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

+// SPDX-License-Identifier: GPL-2.0
+/* Copyright 2022 Sony Group Corporation */
+#include <vmlinux.h>
+
+#include <bpf/bpf_core_read.h>
+#include <bpf/bpf_helpers.h>
+#include <bpf/bpf_tracing.h>
+#include "bpf_misc.h"
+
+int arg1 = 0;
+unsigned long arg2 = 0;
+unsigned long arg3 = 0;
+unsigned long arg4_cx = 0;
+unsigned long arg4 = 0;
+unsigned long arg5 = 0;
+
+int arg1_core = 0;
+unsigned long arg2_core = 0;
+unsigned long arg3_core = 0;
+unsigned long arg4_core_cx = 0;
+unsigned long arg4_core = 0;
+unsigned long arg5_core = 0;
+
+const volatile pid_t filter_pid = 0;
+
+SEC("kprobe/" SYS_PREFIX "sys_prctl")
+int BPF_KPROBE(handle_sys_prctl)
+{
+	struct pt_regs *real_regs;
+	pid_t pid = bpf_get_current_pid_tgid() >> 32;
+
+	if (pid != filter_pid)
+		return 0;
+
+	real_regs = (struct pt_regs *)PT_REGS_PARM1(ctx);
+
+	/* test for PT_REGS_PARM */
+	bpf_probe_read_kernel(&arg1, sizeof(arg1), &PT_REGS_PARM1_SYSCALL(real_regs));
+	bpf_probe_read_kernel(&arg2, sizeof(arg2), &PT_REGS_PARM2_SYSCALL(real_regs));
+	bpf_probe_read_kernel(&arg3, sizeof(arg3), &PT_REGS_PARM3_SYSCALL(real_regs));
+	bpf_probe_read_kernel(&arg4_cx, sizeof(arg4_cx), &PT_REGS_PARM4(real_regs));
+	bpf_probe_read_kernel(&arg4, sizeof(arg4), &PT_REGS_PARM4_SYSCALL(real_regs));
+	bpf_probe_read_kernel(&arg5, sizeof(arg5), &PT_REGS_PARM5_SYSCALL(real_regs));
+
+	/* test for the CORE variant of PT_REGS_PARM */
+	arg1_core = PT_REGS_PARM1_CORE_SYSCALL(real_regs);
+	arg2_core = PT_REGS_PARM2_CORE_SYSCALL(real_regs);
+	arg3_core = PT_REGS_PARM3_CORE_SYSCALL(real_regs);
+	arg4_core_cx = PT_REGS_PARM4_CORE(real_regs);
+	arg4_core = PT_REGS_PARM4_CORE_SYSCALL(real_regs);
+	arg5_core = PT_REGS_PARM5_CORE_SYSCALL(real_regs);
+
+	return 0;
+}
+
+char _license[] SEC("license") = "GPL";