diff --git a/kernel/src/memory.rs b/kernel/src/memory.rs
index 955020f..cbd828d 100644
--- a/kernel/src/memory.rs
+++ b/kernel/src/memory.rs
@@ -171,8 +171,9 @@ pub fn enlarge_heap(heap: &mut Heap) {
     }
 }
 
-pub fn access_ok(from: usize, len: usize) -> bool {
-    from < PHYSICAL_MEMORY_OFFSET && (from + len) < PHYSICAL_MEMORY_OFFSET
+/// Check whether the address range [addr, addr + len) is not in kernel space
+pub fn access_ok(addr: usize, len: usize) -> bool {
+    addr < PHYSICAL_MEMORY_OFFSET && (addr + len) < PHYSICAL_MEMORY_OFFSET
 }
 
 #[naked]
@@ -180,39 +181,19 @@ pub unsafe extern "C" fn read_user_fixup() -> usize {
     return 1;
 }
 
-#[no_mangle]
-pub fn copy_from_user_u8(addr: *const u8) -> Option<u8> {
+pub fn copy_from_user<T>(addr: *const T) -> Option<T> {
     #[naked]
     #[inline(never)]
     #[link_section = ".text.copy_user"]
-    unsafe extern "C" fn read_user_u8(dst: *mut u8, src: *const u8) -> usize {
+    unsafe extern "C" fn read_user<T>(dst: *mut T, src: *const T) -> usize {
         dst.copy_from_nonoverlapping(src, 1);
         0
     }
-    if !access_ok(addr as usize, size_of::<u8>()) {
+    if !access_ok(addr as usize, size_of::<T>()) {
         return None;
     }
-    let mut dst: u8 = 0;
-    match unsafe { read_user_u8((&mut dst) as *mut u8, addr) } {
-        0 => Some(dst),
-        _ => None,
-    }
-}
-
-#[no_mangle]
-pub fn copy_from_user_usize(addr: *const usize) -> Option<usize> {
-    #[naked]
-    #[inline(never)]
-    #[link_section = ".text.copy_user"]
-    unsafe extern "C" fn read_user_usize(dst: *mut usize, src: *const usize) -> usize {
-        dst.copy_from_nonoverlapping(src, 1);
-        0
-    }
-    if !access_ok(addr as usize, size_of::<usize>()) {
-        return None;
-    }
-    let mut dst: usize = 0;
-    match unsafe { read_user_usize((&mut dst) as *mut usize, addr) } {
+    let mut dst: T = unsafe { core::mem::uninitialized() };
+    match unsafe { read_user(&mut dst, addr) } {
         0 => Some(dst),
         _ => None,
     }
diff --git a/kernel/src/syscall/mod.rs b/kernel/src/syscall/mod.rs
index 1e5fe1e..cc4086d 100644
--- a/kernel/src/syscall/mod.rs
+++ b/kernel/src/syscall/mod.rs
@@ -10,7 +10,7 @@ use rcore_memory::VMError;
 use crate::arch::cpu;
 use crate::arch::interrupt::TrapFrame;
 use crate::arch::syscall::*;
-use crate::memory::{copy_from_user_u8, copy_from_user_usize, MemorySet};
+use crate::memory::{copy_from_user, MemorySet};
 use crate::process::*;
 use crate::sync::{Condvar, MutexGuard, SpinNoIrq};
 use crate::thread;
@@ -561,33 +561,25 @@ pub fn check_and_clone_cstr(user: *const u8) -> Result<String, SysError> {
     let mut buffer = Vec::new();
     for i in 0.. {
         let addr = unsafe { user.add(i) };
-        if let Some(data) = copy_from_user_u8(addr) {
-            if data > 0 {
-                buffer.push(data);
-            } else {
-                break;
-            }
-        } else {
-            return Err(SysError::EFAULT);
+        let data = copy_from_user(addr).ok_or(SysError::EFAULT)?;
+        if data == 0 {
+            break;
         }
+        buffer.push(data);
     }
-    return String::from_utf8(buffer).map_err(|_| SysError::EFAULT);
+    String::from_utf8(buffer).map_err(|_| SysError::EFAULT)
 }
 
 pub fn check_and_clone_cstr_array(user: *const *const u8) -> Result<Vec<String>, SysError> {
     let mut buffer = Vec::new();
     for i in 0.. {
         let addr = unsafe { user.add(i) };
-        if let Some(str_addr) = copy_from_user_usize(addr as *const usize) {
-            if str_addr > 0 {
-                let string = check_and_clone_cstr(str_addr as *const u8)?;
-                buffer.push(string);
-            } else {
-                break;
-            }
-        } else {
-            return Err(SysError::EFAULT);
+        let str_ptr = copy_from_user(addr).ok_or(SysError::EFAULT)?;
+        if str_ptr.is_null() {
+            break;
         }
+        let string = check_and_clone_cstr(str_ptr)?;
+        buffer.push(string);
     }
-    return Ok(buffer);
+    Ok(buffer)
 }