/* $NetBSD: ct.c,v 1.2 2017/01/28 21:31:50 christos Exp $ */ /* * Copyright (c) 2009 Kungliga Tekniska Högskolan * (Royal Institute of Technology, Stockholm, Sweden). * All rights reserved. * * Redistribution and use in source and binary forms, with or without * modification, are permitted provided that the following conditions * are met: * * 1. Redistributions of source code must retain the above copyright * notice, this list of conditions and the following disclaimer. * * 2. Redistributions in binary form must reproduce the above copyright * notice, this list of conditions and the following disclaimer in the * documentation and/or other materials provided with the distribution. * * 3. Neither the name of the Institute nor the names of its contributors * may be used to endorse or promote products derived from this software * without specific prior written permission. * * THIS SOFTWARE IS PROVIDED BY THE INSTITUTE AND CONTRIBUTORS ``AS IS'' AND * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE * ARE DISCLAIMED. IN NO EVENT SHALL THE INSTITUTE OR CONTRIBUTORS BE LIABLE * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF * SUCH DAMAGE. */ #include <config.h> #include <krb5/roken.h> /** * Constant time compare to memory regions. The reason for making it * constant time is to make sure that timeing information leak from * where in the function the diffrence is. * * ct_memcmp() can't be used to order memory regions like memcmp(), * for example, use ct_memcmp() with qsort(). * * We use volatile to avoid optimizations where the compiler and/or * linker turn this ct_memcmp() into a plain memcmp(). The pointers * themselves are also marked volatile (not just the memory pointed at) * because in some GCC versions there is a bug which can be worked * around by doing this. * * @param p1 memory region 1 to compare * @param p2 memory region 2 to compare * @param len length of memory * * @return 0 when the memory regions are equal, non zero if not * * @ingroup roken */ int ct_memcmp(const volatile void * volatile p1, const volatile void * volatile p2, size_t len) { /* * There's no need for s1 and s2 to be volatile; only p1 and p2 have * to be in order to work around GCC bugs. * * However, s1 and s2 do have to point to volatile, as we don't know * if the object was originally defined as volatile, and if it was * then we'd get undefined behavior here if s1/s2 were declared to * point to non-volatile memory. */ const volatile unsigned char *s1 = p1; const volatile unsigned char *s2 = p2; size_t i; int r = 0; for (i = 0; i < len; i++) r |= (s1[i] ^ s2[i]); return !!r; } |