arm64: don't zero in __copy_from_user{,_inatomic}

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

arch/arm64/include/asm/uaccess.h

@@ -278,14 +278,16 @@ static inline unsigned long __must_check __copy_to_user(void __user *to, const v
 
 static inline unsigned long __must_check copy_from_user(void *to, const void __user *from, unsigned long n)
 {
+	unsigned long res = n;
 	kasan_check_write(to, n);
 
 	if (access_ok(VERIFY_READ, from, n)) {
 		check_object_size(to, n, false);
-		n = __arch_copy_from_user(to, from, n);
-	} else /* security hole - plug it */
-		memset(to, 0, n);
-	return n;
+		res = __arch_copy_from_user(to, from, n);
+	}
+	if (unlikely(res))
+		memset(to + (n - res), 0, res);
+	return res;
 }
 
 static inline unsigned long __must_check copy_to_user(void __user *to, const void *from, unsigned long n)

arch/arm64/lib/copy_from_user.S

@@ -79,11 +79,6 @@ ENDPROC(__arch_copy_from_user)
 
 	.section .fixup,"ax"
 	.align	2
-9998:
-	sub	x0, end, dst
-9999:
-	strb	wzr, [dst], #1			// zero remaining buffer space
-	cmp	dst, end
-	b.lo	9999b
+9998:	sub	x0, end, dst			// bytes not copied
 	ret
 	.previous