From f93a41877d8d7a287debb7c63d7b646abaaf269c Mon Sep 17 00:00:00 2001 From: Andy Polyakov Date: Fri, 8 Feb 2013 21:30:52 +0100 Subject: [PATCH] s3_cbc.c: make CBC_MAC_ROTATE_IN_PLACE universal. --- ssl/s3_cbc.c | 17 +++++++++-------- 1 file changed, 9 insertions(+), 8 deletions(-) diff --git a/ssl/s3_cbc.c b/ssl/s3_cbc.c index 005451a3b6..2e93657973 100644 --- a/ssl/s3_cbc.c +++ b/ssl/s3_cbc.c @@ -229,10 +229,6 @@ int tls1_cbc_remove_padding(const SSL* s, return (int)((good & 1) | (~good & -1)); } -#if defined(_M_AMD64) || defined(__x86_64__) -#define CBC_MAC_ROTATE_IN_PLACE -#endif - /* ssl3_cbc_copy_mac copies |md_size| bytes from the end of |rec| to |out| in * constant time (independent of the concrete value of rec->length, which may * vary within a 256-byte window). @@ -246,15 +242,18 @@ int tls1_cbc_remove_padding(const SSL* s, * * If CBC_MAC_ROTATE_IN_PLACE is defined then the rotation is performed with * variable accesses in a 64-byte-aligned buffer. Assuming that this fits into - * a single cache-line, then the variable memory accesses don't actually affect - * the timing. This has been tested to be true on Intel amd64 chips. + * a single or pair of cache-lines, then the variable memory accesses don't + * actually affect the timing. CPUs with smaller cache-lines [if any] are + * not multi-core and are not considered vulnerable to cache-timing attacks. */ +#define CBC_MAC_ROTATE_IN_PLACE + void ssl3_cbc_copy_mac(unsigned char* out, const SSL3_RECORD *rec, unsigned md_size) { #if defined(CBC_MAC_ROTATE_IN_PLACE) - unsigned char rotated_mac_buf[EVP_MAX_MD_SIZE*2]; + unsigned char rotated_mac_buf[64+EVP_MAX_MD_SIZE]; unsigned char *rotated_mac; #else unsigned char rotated_mac[EVP_MAX_MD_SIZE]; @@ -274,7 +273,7 @@ void ssl3_cbc_copy_mac(unsigned char* out, OPENSSL_assert(md_size <= EVP_MAX_MD_SIZE); #if defined(CBC_MAC_ROTATE_IN_PLACE) - rotated_mac = (unsigned char*) (((intptr_t)(rotated_mac_buf + 64)) & ~63); + rotated_mac = rotated_mac_buf + ((0-(size_t)rotated_mac_buf)&63); #endif /* This information is public so it's safe to branch based on it. */ @@ -306,6 +305,8 @@ void ssl3_cbc_copy_mac(unsigned char* out, j = 0; for (i = 0; i < md_size; i++) { + /* in case cache-line is 32 bytes, touch second line */ + ((volatile unsigned char *)rotated_mac)[rotate_offset^32]; out[j++] = rotated_mac[rotate_offset++]; rotate_offset &= constant_time_lt(rotate_offset,md_size); } -- 2.25.1