diff options
| author | basavesh <basavesh.shivakumar@gmail.com> | 2022-04-05 17:49:09 +0200 |
|---|---|---|
| committer | Tomas Mraz <tomas@openssl.org> | 2022-05-09 16:41:29 +0200 |
| commit | 6ef91d8153e04a2302bff11b29caf7e888b62fe8 (patch) | |
| tree | edd6eafbaff6fa93ac5cc2bf74f6f3cd446315da /ssl | |
| parent | c7d6c08290b67cbeef2b4f636f04788ea405520a (diff) | |
Fix leakage when the cacheline is 32-bytes in CBC_MAC_ROTATE_IN_PLACE
rotated_mac is a 64-byte aligned buffer of size 64 and rotate_offset is secret.
Consider a weaker leakage model(CL) where only cacheline base address is leaked,
i.e address/32 for 32-byte cacheline(CL32).
Previous code used to perform two loads
1. rotated_mac[rotate_offset ^ 32] and
2. rotated_mac[rotate_offset++]
which would leak 2q + 1, 2q for 0 <= rotate_offset < 32
and 2q, 2q + 1 for 32 <= rotate_offset < 64
The proposed fix performs load operations which will always leak 2q, 2q + 1 and
selects the appropriate value in constant-time.
Reviewed-by: Matt Caswell <matt@openssl.org>
Reviewed-by: Tomas Mraz <tomas@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/18050)
Diffstat (limited to 'ssl')
| -rw-r--r-- | ssl/record/ssl3_record.c | 14 |
1 files changed, 11 insertions, 3 deletions
diff --git a/ssl/record/ssl3_record.c b/ssl/record/ssl3_record.c index f158544789..69f1a64cb3 100644 --- a/ssl/record/ssl3_record.c +++ b/ssl/record/ssl3_record.c @@ -1532,6 +1532,7 @@ int ssl3_cbc_copy_mac(unsigned char *out, #if defined(CBC_MAC_ROTATE_IN_PLACE) unsigned char rotated_mac_buf[64 + EVP_MAX_MD_SIZE]; unsigned char *rotated_mac; + char aux1, aux2, aux3, mask; #else unsigned char rotated_mac[EVP_MAX_MD_SIZE]; #endif @@ -1581,9 +1582,16 @@ int ssl3_cbc_copy_mac(unsigned char *out, #if defined(CBC_MAC_ROTATE_IN_PLACE) 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++]; + /* + * in case cache-line is 32 bytes, + * load from both lines and select appropriately + */ + aux1 = rotated_mac[rotate_offset & ~32]; + aux2 = rotated_mac[rotate_offset | 32]; + mask = constant_time_eq_8(rotate_offset & ~32, rotate_offset); + aux3 = constant_time_select_8(mask, aux1, aux2); + out[j++] = aux3; + rotate_offset++; rotate_offset &= constant_time_lt_s(rotate_offset, md_size); } #else |