selftests/seccomp: arm64: Define SYSCALL_NUM_SET macro

Remove the arm64 special-case in change_syscall().
Signed-off-by: Kees Cook <keescook@chromium.org>
Link: https://lore.kernel.org/lkml/20200912110820.597135-6-keescook@chromium.orgAcked-by: Christian Brauner <christian.brauner@ubuntu.com>

tools/testing/selftests/seccomp/seccomp_bpf.c

@@ -1717,6 +1717,18 @@ TEST_F(TRACE_poke, getpid_runs_normally)
 #elif defined(__aarch64__)
 # define ARCH_REGS		struct user_pt_regs
 # define SYSCALL_NUM(_regs)	(_regs).regs[8]
+# ifndef NT_ARM_SYSTEM_CALL
+#  define NT_ARM_SYSTEM_CALL 0x404
+# endif
+# define SYSCALL_NUM_SET(_regs, _nr)				\
+	do {							\
+		struct iovec __v;				\
+		typeof(_nr) __nr = (_nr);			\
+		__v.iov_base = &__nr;				\
+		__v.iov_len = sizeof(__nr);			\
+		EXPECT_EQ(0, ptrace(PTRACE_SETREGSET, tracee,	\
+				    NT_ARM_SYSTEM_CALL, &__v));	\
+	} while (0)
 # define SYSCALL_RET(_regs)	(_regs).regs[0]
 #elif defined(__riscv) && __riscv_xlen == 64
 # define ARCH_REGS		struct user_regs_struct
@@ -1852,23 +1864,10 @@ void change_syscall(struct __test_metadata *_metadata,
 #if defined(__x86_64__) || defined(__i386__) || defined(__powerpc__) || \
 	defined(__s390__) || defined(__hppa__) || defined(__riscv) || \
 	defined(__xtensa__) || defined(__csky__) || defined(__sh__) || \
-	defined(__mips__) || defined(__arm__)
+	defined(__mips__) || defined(__arm__) || defined(__aarch64__)
 	{
 		SYSCALL_NUM_SET(regs, syscall);
 	}
-
-#elif defined(__aarch64__)
-# ifndef NT_ARM_SYSTEM_CALL
-#  define NT_ARM_SYSTEM_CALL 0x404
-# endif
-	{
-		iov.iov_base = &syscall;
-		iov.iov_len = sizeof(syscall);
-		ret = ptrace(PTRACE_SETREGSET, tracee, NT_ARM_SYSTEM_CALL,
-			     &iov);
-		EXPECT_EQ(0, ret);
-	}
-
 #else
 	ASSERT_EQ(1, 0) {
 		TH_LOG("How is the syscall changed on this architecture?");