From aa050a7bdb943ca94ab914f2a9dc508e09a57431 Mon Sep 17 00:00:00 2001 From: Antonio Nino Diaz Date: Mon, 16 Jan 2017 13:25:38 +0000 Subject: [PATCH] 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 Signed-off-by: Antonio Nino Diaz --- include/lib/stdlib/string.h | 1 + lib/stdlib/stdlib.mk | 3 ++- lib/stdlib/timingsafe_bcmp.c | 36 ++++++++++++++++++++++++++++++++++++ 3 files changed, 39 insertions(+), 1 deletion(-) create mode 100644 lib/stdlib/timingsafe_bcmp.c diff --git a/include/lib/stdlib/string.h b/include/lib/stdlib/string.h index 9beeb448a..902d9c130 100644 --- a/include/lib/stdlib/string.h +++ b/include/lib/stdlib/string.h @@ -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 diff --git a/lib/stdlib/stdlib.mk b/lib/stdlib/stdlib.mk index 4ff405fb6..533271744 100644 --- a/lib/stdlib/stdlib.mk +++ b/lib/stdlib/stdlib.mk @@ -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 diff --git a/lib/stdlib/timingsafe_bcmp.c b/lib/stdlib/timingsafe_bcmp.c new file mode 100644 index 000000000..d09815805 --- /dev/null +++ b/lib/stdlib/timingsafe_bcmp.c @@ -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 +__FBSDID("$FreeBSD$"); + +#include + +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);