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stdlib: Import timingsafe_bcmp() from FreeBSD 

Some side-channel attacks involve an attacker inferring something from
the time taken for a memory compare operation to complete, for example
when comparing hashes during image authentication. To mitigate this,
timingsafe_bcmp() must be used for such operations instead of the
standard memcmp().

This function executes in constant time and so doesn't leak any timing
information to the caller.

Change-Id: I470a723dc3626a0ee6d5e3f7fd48d0a57b8aa5fd
Signed-off-by: dp-arm <dimitris.papastamos@arm.com>
Signed-off-by: Antonio Nino Diaz <antonio.ninodiaz@arm.com>
This commit is contained in:
Antonio Nino Diaz 2017-01-16 13:25:38 +00:00
parent 34438669d4
commit aa050a7bdb
3 changed files with 39 additions and 1 deletions
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1
include/lib/stdlib/string.h
View File

@ -61,6 +61,7 @@ size_t strlen(const char *) __pure;
int strncmp(const char *, const char *, size_t) __pure;
size_t strnlen(const char *, size_t) __pure;
int strcasecmp(const char *, const char *);
int timingsafe_bcmp(const void *, const void *, size_t);
__END_DECLS

3
lib/stdlib/stdlib.mk
View File

@ -42,7 +42,8 @@ STDLIB_SRCS := $(addprefix lib/stdlib/, \
strlen.c \
strncmp.c \
strnlen.c \
subr_prf.c)
subr_prf.c \
timingsafe_bcmp.c)
INCLUDES += -Iinclude/lib/stdlib \
-Iinclude/lib/stdlib/sys

36
lib/stdlib/timingsafe_bcmp.c Normal file
View File

@ -0,0 +1,36 @@
/* $OpenBSD: timingsafe_bcmp.c,v 1.3 2015/08/31 02:53:57 guenther Exp $ */
/*
* Copyright (c) 2010 Damien Miller. All rights reserved.
*
* Permission to use, copy, modify, and distribute this software for any
* purpose with or without fee is hereby granted, provided that the above
* copyright notice and this permission notice appear in all copies.
*
* THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
* WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
* MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
* ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
* WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
* ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
* OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
*/
#include <sys/cdefs.h>
__FBSDID("$FreeBSD$");
#include <string.h>
int __timingsafe_bcmp(const void *, const void *, size_t);
int
__timingsafe_bcmp(const void *b1, const void *b2, size_t n)
{
const unsigned char *p1 = b1, *p2 = b2;
int ret = 0;
for (; n > 0; n--)
ret |= *p1++ ^ *p2++;
return (ret != 0);
}
__weak_reference(__timingsafe_bcmp, timingsafe_bcmp);