Merge pull request #817 from antonio-nino-diaz-arm/an/timingsafe

Import constant-time bcmp() and use it where necessary

drivers/auth/mbedtls/mbedtls_crypto.c

@@ -217,7 +217,7 @@ static int verify_hash(void *data_ptr, unsigned int data_len,
 	}
 
 	/* Compare values */
-	rc = memcmp(data_hash, hash, mbedtls_md_get_size(md_info));
+	rc = timingsafe_bcmp(data_hash, hash, mbedtls_md_get_size(md_info));
 	if (rc != 0) {
 		return CRYPTO_ERR_HASH;
 	}

drivers/auth/mbedtls/mbedtls_x509_parser.c

@@ -392,7 +392,7 @@ static int cert_parse(void *img, unsigned int img_len)
 	if (sig_alg1.len != sig_alg2.len) {
 		return IMG_PARSER_ERR_FORMAT;
 	}
-	if (0 != memcmp(sig_alg1.p, sig_alg2.p, sig_alg1.len)) {
+	if (0 != timingsafe_bcmp(sig_alg1.p, sig_alg2.p, sig_alg1.len)) {
 		return IMG_PARSER_ERR_FORMAT;
 	}
 	memcpy(&sig_alg, &sig_alg1, sizeof(sig_alg));

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
 

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

lib/stdlib/timingsafe_bcmp.c

+/*	$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);