diff --git a/arch/um/sys-i386/ldt.c b/arch/um/sys-i386/ldt.c
index dc755b0b9db8..bd3c34aa52e5 100644
--- a/arch/um/sys-i386/ldt.c
+++ b/arch/um/sys-i386/ldt.c
@@ -4,96 +4,106 @@
  */
 
 #include "linux/config.h"
+#include "linux/sched.h"
 #include "linux/slab.h"
+#include "linux/types.h"
 #include "asm/uaccess.h"
 #include "asm/ptrace.h"
+#include "asm/smp.h"
+#include "asm/ldt.h"
 #include "choose-mode.h"
 #include "kern.h"
+#include "mode_kern.h"
 
 #ifdef CONFIG_MODE_TT
+
 extern int modify_ldt(int func, void *ptr, unsigned long bytecount);
 
-/* XXX this needs copy_to_user and copy_from_user */
-
-int sys_modify_ldt_tt(int func, void __user *ptr, unsigned long bytecount)
+static int do_modify_ldt_tt(int func, void *ptr, unsigned long bytecount)
 {
-	if (!access_ok(VERIFY_READ, ptr, bytecount))
-		return -EFAULT;
-
 	return modify_ldt(func, ptr, bytecount);
 }
+
 #endif
 
 #ifdef CONFIG_MODE_SKAS
-extern int userspace_pid[];
 
+#include "skas.h"
 #include "skas_ptrace.h"
 
-int sys_modify_ldt_skas(int func, void __user *ptr, unsigned long bytecount)
+static int do_modify_ldt_skas(int func, void *ptr, unsigned long bytecount)
 {
 	struct ptrace_ldt ldt;
-	void *buf;
-	int res, n;
+	u32 cpu;
+	int res;
 
-	buf = kmalloc(bytecount, GFP_KERNEL);
-	if(buf == NULL)
-		return(-ENOMEM);
+	ldt = ((struct ptrace_ldt) { .func	= func,
+				     .ptr	= ptr,
+				     .bytecount = bytecount });
 
-	res = 0;
+	cpu = get_cpu();
+	res = ptrace(PTRACE_LDT, userspace_pid[cpu], 0, (unsigned long) &ldt);
+	put_cpu();
+
+	return res;
+}
+#endif
+
+int sys_modify_ldt(int func, void __user *ptr, unsigned long bytecount)
+{
+	struct user_desc info;
+	int res = 0;
+	void *buf = NULL;
+	void *p = NULL; /* What we pass to host. */
 
 	switch(func){
 	case 1:
-	case 0x11:
-		res = copy_from_user(buf, ptr, bytecount);
-		break;
-	}
+	case 0x11: /* write_ldt */
+		/* Do this check now to avoid overflows. */
+		if (bytecount != sizeof(struct user_desc)) {
+			res = -EINVAL;
+			goto out;
+		}
 
-	if(res != 0){
-		res = -EFAULT;
+		if(copy_from_user(&info, ptr, sizeof(info))) {
+			res = -EFAULT;
+			goto out;
+		}
+
+		p = &info;
+		break;
+	case 0:
+	case 2: /* read_ldt */
+
+		/* The use of info avoids kmalloc on the write case, not on the
+		 * read one. */
+		buf = kmalloc(bytecount, GFP_KERNEL);
+		if (!buf) {
+			res = -ENOMEM;
+			goto out;
+		}
+		p = buf;
+	default:
+		res = -ENOSYS;
 		goto out;
 	}
 
-	ldt = ((struct ptrace_ldt) { .func	= func,
-				     .ptr	= buf,
-				     .bytecount = bytecount });
-#warning Need to look up userspace_pid by cpu
-	res = ptrace(PTRACE_LDT, userspace_pid[0], 0, (unsigned long) &ldt);
+	res = CHOOSE_MODE_PROC(do_modify_ldt_tt, do_modify_ldt_skas, func,
+				p, bytecount);
 	if(res < 0)
 		goto out;
 
 	switch(func){
 	case 0:
 	case 2:
-		n = res;
-		res = copy_to_user(ptr, buf, n);
-		if(res != 0)
+		/* Modify_ldt was for reading and returned the number of read
+		 * bytes.*/
+		if(copy_to_user(ptr, p, res))
 			res = -EFAULT;
-		else 
-			res = n;
 		break;
 	}
 
- out:
+out:
 	kfree(buf);
-	return(res);
+	return res;
 }
-#endif
-
-int sys_modify_ldt(int func, void __user *ptr, unsigned long bytecount)
-{
-	return(CHOOSE_MODE_PROC(sys_modify_ldt_tt, sys_modify_ldt_skas, func, 
-				ptr, bytecount));
-}
-
-
-
-/*
- * Overrides for Emacs so that we follow Linus's tabbing style.
- * Emacs will notice this stuff at the end of the file and automatically
- * adjust the settings for this buffer only.  This must remain at the end
- * of the file.
- * ---------------------------------------------------------------------------
- * Local variables:
- * c-file-style: "linux"
- * End:
- */
diff --git a/include/asm-um/ldt.h b/include/asm-um/ldt.h
new file mode 100644
index 000000000000..e908439d338a
--- /dev/null
+++ b/include/asm-um/ldt.h
@@ -0,0 +1,5 @@
+#ifndef __UM_LDT_H
+#define __UM_LDT_H
+
+#include "asm/arch/ldt.h"
+#endif