[S390] uaccess: Always access the correct address space.

The current uaccess page table walk code assumes at a few places that
any access is a user space access. This is not correct if somebody
has issued a set_fs(KERNEL_DS) in advance.
Add code which checks which address space we are in and with this make
sure we access the correct address space. This way we get also rid of
the dirty
if (!currrent-mm)
	return -EFAULT;
hack in futex_atomic_cmpxchg_pt.

Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>

arch/s390/lib/uaccess_pt.c

@@ -302,6 +302,10 @@ static size_t copy_in_user_pt(size_t n, void __user *to,
 	pte_t *pte_from, *pte_to;
 	int write_user;
 
+	if (segment_eq(get_fs(), KERNEL_DS)) {
+		memcpy((void __force *) to, (void __force *) from, n);
+		return 0;
+	}
 	done = 0;
 retry:
 	spin_lock(&mm->page_table_lock);
@@ -361,18 +365,10 @@ fault:
 		     : "0" (-EFAULT), "d" (oparg), "a" (uaddr),		\
 		       "m" (*uaddr) : "cc" );
 
-int futex_atomic_op_pt(int op, int __user *uaddr, int oparg, int *old)
+static int __futex_atomic_op_pt(int op, int __user *uaddr, int oparg, int *old)
 {
 	int oldval = 0, newval, ret;
 
-	spin_lock(&current->mm->page_table_lock);
-	uaddr = (int __user *) __dat_user_addr((unsigned long) uaddr);
-	if (!uaddr) {
-		spin_unlock(&current->mm->page_table_lock);
-		return -EFAULT;
-	}
-	get_page(virt_to_page(uaddr));
-	spin_unlock(&current->mm->page_table_lock);
 	switch (op) {
 	case FUTEX_OP_SET:
 		__futex_atomic_op("lr %2,%5\n",
@@ -397,17 +393,17 @@ int futex_atomic_op_pt(int op, int __user *uaddr, int oparg, int *old)
 	default:
 		ret = -ENOSYS;
 	}
-	put_page(virt_to_page(uaddr));
-	*old = oldval;
+	if (ret == 0)
+		*old = oldval;
 	return ret;
 }
 
-int futex_atomic_cmpxchg_pt(int __user *uaddr, int oldval, int newval)
+int futex_atomic_op_pt(int op, int __user *uaddr, int oparg, int *old)
 {
 	int ret;
 
-	if (!current->mm)
-		return -EFAULT;
+	if (segment_eq(get_fs(), KERNEL_DS))
+		return __futex_atomic_op_pt(op, uaddr, oparg, old);
 	spin_lock(&current->mm->page_table_lock);
 	uaddr = (int __user *) __dat_user_addr((unsigned long) uaddr);
 	if (!uaddr) {
@@ -416,13 +412,40 @@ int futex_atomic_cmpxchg_pt(int __user *uaddr, int oldval, int newval)
 	}
 	get_page(virt_to_page(uaddr));
 	spin_unlock(&current->mm->page_table_lock);
-	asm volatile("   cs   %1,%4,0(%5)\n"
-		     "0: lr   %0,%1\n"
-		     "1:\n"
-		     EX_TABLE(0b,1b)
+	ret = __futex_atomic_op_pt(op, uaddr, oparg, old);
+	put_page(virt_to_page(uaddr));
+	return ret;
+}
+
+static int __futex_atomic_cmpxchg_pt(int __user *uaddr, int oldval, int newval)
+{
+	int ret;
+
+	asm volatile("0: cs   %1,%4,0(%5)\n"
+		     "1: lr   %0,%1\n"
+		     "2:\n"
+		     EX_TABLE(0b,2b) EX_TABLE(1b,2b)
 		     : "=d" (ret), "+d" (oldval), "=m" (*uaddr)
 		     : "0" (-EFAULT), "d" (newval), "a" (uaddr), "m" (*uaddr)
 		     : "cc", "memory" );
+	return ret;
+}
+
+int futex_atomic_cmpxchg_pt(int __user *uaddr, int oldval, int newval)
+{
+	int ret;
+
+	if (segment_eq(get_fs(), KERNEL_DS))
+		return __futex_atomic_cmpxchg_pt(uaddr, oldval, newval);
+	spin_lock(&current->mm->page_table_lock);
+	uaddr = (int __user *) __dat_user_addr((unsigned long) uaddr);
+	if (!uaddr) {
+		spin_unlock(&current->mm->page_table_lock);
+		return -EFAULT;
+	}
+	get_page(virt_to_page(uaddr));
+	spin_unlock(&current->mm->page_table_lock);
+	ret = __futex_atomic_cmpxchg_pt(uaddr, oldval, newval);
 	put_page(virt_to_page(uaddr));
 	return ret;
 }