@@ -21,6 +21,9 @@
 
 #define TASK_SIZE_64		(UL(1) << VA_BITS)
 
+#define KERNEL_DS	UL(-1)
+#define USER_DS		(TASK_SIZE_64 - 1)
+
 #ifndef __ASSEMBLY__
 
 /*

@@ -56,10 +56,7 @@ struct exception_table_entry
 
 extern int fixup_exception(struct pt_regs *regs);
 
-#define KERNEL_DS	(-1UL)
 #define get_ds()	(KERNEL_DS)
-
-#define USER_DS		TASK_SIZE_64
 #define get_fs()	(current_thread_info()->addr_limit)
 
 static inline void set_fs(mm_segment_t fs)

@@ -87,22 +84,32 @@ static inline void set_fs(mm_segment_t fs)
  * Returns 1 if the range is valid, 0 otherwise.
  *
  * This is equivalent to the following test:
- * (u65)addr + (u65)size <= current->addr_limit
- *
- * This needs 65-bit arithmetic.
+ * (u65)addr + (u65)size <= (u65)current->addr_limit + 1
  */
-#define __range_ok(addr, size)						\
-({									\
-	unsigned long __addr = (unsigned long __force)(addr);		\
-	unsigned long flag, roksum;					\
-	__chk_user_ptr(addr);						\
-	asm("adds %1, %1, %3; ccmp %1, %4, #2, cc; cset %0, ls"		\
-		: "=&r" (flag), "=&r" (roksum)				\
-		: "1" (__addr), "Ir" (size),				\
-		  "r" (current_thread_info()->addr_limit)		\
-		: "cc");						\
-	flag;								\
-})
+static inline unsigned long __range_ok(unsigned long addr, unsigned long size)
+{
+	unsigned long limit = current_thread_info()->addr_limit;
+
+	__chk_user_ptr(addr);
+	asm volatile(
+	// A + B <= C + 1 for all A,B,C, in four easy steps:
+	// 1: X = A + B; X' = X % 2^64
+	"	adds	%0, %0, %2\n"
+	// 2: Set C = 0 if X > 2^64, to guarantee X' > C in step 4
+	"	csel	%1, xzr, %1, hi\n"
+	// 3: Set X' = ~0 if X >= 2^64. For X == 2^64, this decrements X'
+	//    to compensate for the carry flag being set in step 4. For
+	//    X > 2^64, X' merely has to remain nonzero, which it does.
+	"	csinv	%0, %0, xzr, cc\n"
+	// 4: For X < 2^64, this gives us X' - C - 1 <= 0, where the -1
+	//    comes from the carry in being clear. Otherwise, we are
+	//    testing X' - C == 0, subject to the previous adjustments.
+	"	sbcs	xzr, %0, %1\n"
+	"	cset	%0, ls\n"
+	: "+r" (addr), "+r" (limit) : "Ir" (size) : "cc");
+
+	return addr;
+}
 
 /*
  * When dealing with data aborts, watchpoints, or instruction traps we may end

@@ -111,7 +118,7 @@ static inline void set_fs(mm_segment_t fs)
  */
 #define untagged_addr(addr)		sign_extend64(addr, 55)
 
-#define access_ok(type, addr, size)	__range_ok(addr, size)
+#define access_ok(type, addr, size)	__range_ok((unsigned long)(addr), size)
 #define user_addr_max			get_fs
 
 /*

@@ -96,10 +96,10 @@
 	.else
 	add	x21, sp, #S_FRAME_SIZE
 	get_thread_info tsk
-	/* Save the task's original addr_limit and set USER_DS (TASK_SIZE_64) */
+	/* Save the task's original addr_limit and set USER_DS */
 	ldr	x20, [tsk, #TI_ADDR_LIMIT]
 	str	x20, [sp, #S_ORIG_ADDR_LIMIT]
-	mov	x20, #TASK_SIZE_64
+	mov	x20, #USER_DS
 	str	x20, [tsk, #TI_ADDR_LIMIT]
 	.endif /* \el == 0 */
 	mrs	x22, elr_el1