Line data    Source code

       1             : /*
       2             :  * Copyright (c) 2009 Kungliga Tekniska Högskolan
       3             :  * (Royal Institute of Technology, Stockholm, Sweden).
       4             :  * All rights reserved.
       5             :  *
       6             :  * Redistribution and use in source and binary forms, with or without
       7             :  * modification, are permitted provided that the following conditions
       8             :  * are met:
       9             :  *
      10             :  * 1. Redistributions of source code must retain the above copyright
      11             :  *    notice, this list of conditions and the following disclaimer.
      12             :  *
      13             :  * 2. Redistributions in binary form must reproduce the above copyright
      14             :  *    notice, this list of conditions and the following disclaimer in the
      15             :  *    documentation and/or other materials provided with the distribution.
      16             :  *
      17             :  * 3. Neither the name of the Institute nor the names of its contributors
      18             :  *    may be used to endorse or promote products derived from this software
      19             :  *    without specific prior written permission.
      20             :  *
      21             :  * THIS SOFTWARE IS PROVIDED BY THE INSTITUTE AND CONTRIBUTORS ``AS IS'' AND
      22             :  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
      23             :  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
      24             :  * ARE DISCLAIMED.  IN NO EVENT SHALL THE INSTITUTE OR CONTRIBUTORS BE LIABLE
      25             :  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
      26             :  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
      27             :  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
      28             :  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
      29             :  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
      30             :  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
      31             :  * SUCH DAMAGE.
      32             :  */
      33             : 
      34             : #include <config.h>
      35             : #include "roken.h"
      36             : 
      37             : /**
      38             :  * Constant time compare to memory regions. The reason for making it
      39             :  * constant time is to make sure that timeing information leak from
      40             :  * where in the function the diffrence is.
      41             :  *
      42             :  * ct_memcmp() can't be used to order memory regions like memcmp(),
      43             :  * for example, use ct_memcmp() with qsort().
      44             :  *
      45             :  * We use volatile to avoid optimizations where the compiler and/or
      46             :  * linker turn this ct_memcmp() into a plain memcmp().  The pointers
      47             :  * themselves are also marked volatile (not just the memory pointed at)
      48             :  * because in some GCC versions there is a bug which can be worked
      49             :  * around by doing this.
      50             :  *
      51             :  * @param p1 memory region 1 to compare
      52             :  * @param p2 memory region 2 to compare
      53             :  * @param len length of memory
      54             :  *
      55             :  * @return 0 when the memory regions are equal, non zero if not
      56             :  *
      57             :  * @ingroup roken
      58             :  */
      59             : 
      60             : int
      61     3715608 : ct_memcmp(const volatile void * volatile p1,
      62             :           const volatile void * volatile p2,
      63             :           size_t len)
      64             : {
      65             :     /*
      66             :      * There's no need for s1 and s2 to be volatile; only p1 and p2 have
      67             :      * to be in order to work around GCC bugs.
      68             :      *
      69             :      * However, s1 and s2 do have to point to volatile, as we don't know
      70             :      * if the object was originally defined as volatile, and if it was
      71             :      * then we'd get undefined behavior here if s1/s2 were declared to
      72             :      * point to non-volatile memory.
      73             :      */
      74     3715608 :     const volatile unsigned char *s1 = p1;
      75     3715608 :     const volatile unsigned char *s2 = p2;
      76       29976 :     size_t i;
      77     3715608 :     int r = 0;
      78             : 
      79    49492581 :     for (i = 0; i < len; i++)
      80    45776973 :         r |= (s1[i] ^ s2[i]);
      81     3715608 :     return !!r;
      82             : }