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