commit 84bde419e134a318becb61537459d7365af7f4bd
author Andrzej Kurek <andrzej.kurek@arm.com> Mon Jul 06 15:27:34 2020 -0400
committer Andrzej Kurek <andrzej.kurek@arm.com> Mon Jul 06 15:27:34 2020 -0400
tree 2b887ea4df13526366334e6ba88266ffd19b3ff9
parent 74f7d0f03de292474ed16500575aee45758fa491

Add FI countermeasures to the ssl module

This commit adds mainly buffer pointer and length duplication and checks,
but also some hamming distance and return values checking improvements.
Signed-off-by: Andrzej Kurek <andrzej.kurek@arm.com>

library/ssl_srv.c

diff --git a/library/ssl_srv.c b/library/ssl_srv.c
index d560d35..7094a89 100644
--- a/library/ssl_srv.c
+++ b/library/ssl_srv.c
@@ -3269,13 +3269,19 @@
                            - sig_start );
     int ret = ssl->conf->f_async_resume( ssl,
                                          sig_start, signature_len, sig_max_len );
+    volatile size_t *signature_len_dup = signature_len;
     if( ret != MBEDTLS_ERR_SSL_ASYNC_IN_PROGRESS )
     {
         ssl->handshake->async_in_progress = 0;
         mbedtls_ssl_set_async_operation_data( ssl, NULL );
     }
     MBEDTLS_SSL_DEBUG_RET( 2, "ssl_resume_server_key_exchange", ret );
-    return( ret );
+    /* Secure against buffer substitution */
+    if( signature_len_dup == signature_len )
+    {
+        return( ret );
+    }
+    return( MBEDTLS_ERR_PLATFORM_FAULT_DETECTED );
 }
 #endif /* defined(MBEDTLS_KEY_EXCHANGE__WITH_SERVER_SIGNATURE__ENABLED) &&
           defined(MBEDTLS_SSL_ASYNC_PRIVATE) */
@@ -3678,7 +3684,7 @@
     {
         return( 0 );
     }
-    return MBEDTLS_ERR_PLATFORM_FAULT_DETECTED;
+    return( MBEDTLS_ERR_PLATFORM_FAULT_DETECTED );
 }
 
 /* Prepare the ServerKeyExchange message and send it. For ciphersuites
@@ -3826,6 +3832,8 @@
                                        const unsigned char *end )
 {
     int ret = MBEDTLS_ERR_SSL_FEATURE_UNAVAILABLE;
+    unsigned char ** volatile p_dup = p;
+    volatile const unsigned char *end_dup = end;
     size_t n;
 
     /*
@@ -3856,7 +3864,12 @@
 
     MBEDTLS_SSL_DEBUG_MPI( 3, "DHM: GY", &ssl->handshake->dhm_ctx.GY );
 
-    return( ret );
+    /* Secure against buffer substitution */
+    if( p_dup == p && end_dup == end )
+    {
+        return( ret );
+    }
+    return( MBEDTLS_ERR_PLATFORM_FAULT_DETECTED );
 }
 #endif /* MBEDTLS_KEY_EXCHANGE_DHE_RSA_ENABLED ||
           MBEDTLS_KEY_EXCHANGE_DHE_PSK_ENABLED */
@@ -4423,7 +4436,7 @@
     {
         return( ret );
     }
-    return MBEDTLS_ERR_PLATFORM_FAULT_DETECTED;
+    return( MBEDTLS_ERR_PLATFORM_FAULT_DETECTED );
 }
 
 /* Update the handshake state */