commit e965bd397e2299280184228109fc57847b68b104
author Hanno Becker <hanno.becker@arm.com> Wed Jun 12 14:04:34 2019 +0100
committer Hanno Becker <hanno.becker@arm.com> Fri Jul 12 15:14:51 2019 +0100
tree f53e8f6e35f710dac45110de9865d41eb6a2f487
parent fabfb8578a071254ed2e3751fec937a91c17f731

Allow hardcoding of min/max minor/major SSL version at compile-time

This commit introduces the numeric compile-time constants

- MBEDTLS_SSL_CONF_MIN_MINOR_VER
- MBEDTLS_SSL_CONF_MAX_MINOR_VER
- MBEDTLS_SSL_CONF_MIN_MAJOR_VER
- MBEDTLS_SSL_CONF_MAX_MAJOR_VER

which, when defined, overwrite the runtime configurable fields
mbedtls_ssl_config::min_major_ver etc. in the SSL configuration.

As for the preceding case of the ExtendedMasterSecret configuration,
it also introduces and puts to use getter functions for these variables
which evaluate to either a field access or the macro value, maintaining
readability of the code.

The runtime configuration API mbedtls_ssl_conf_{min|max}_version()
is kept for now but has no effect if MBEDTLS_SSL_CONF_XXX are set.
This is likely to be changed in a later commit but deliberately omitted
for now, in order to be able to study code-size benefits earlier in the
process.

library/ssl_srv.c

diff --git a/library/ssl_srv.c b/library/ssl_srv.c
index e743eff..553ded2 100644
--- a/library/ssl_srv.c
+++ b/library/ssl_srv.c
@@ -1090,15 +1090,17 @@
     }
 
     ssl->major_ver = MBEDTLS_SSL_MAJOR_VERSION_3;
-    ssl->minor_ver = ( buf[4] <= ssl->conf->max_minor_ver )
-                     ? buf[4]  : ssl->conf->max_minor_ver;
+    ssl->minor_ver =
+        ( buf[4] <= mbedtls_ssl_conf_get_max_minor_ver( ssl->conf ) )
+        ? buf[4]  : mbedtls_ssl_conf_get_max_minor_ver( ssl->conf );
 
-    if( ssl->minor_ver < ssl->conf->min_minor_ver )
+    if( ssl->minor_ver < mbedtls_ssl_conf_get_min_minor_ver( ssl->conf ) )
     {
         MBEDTLS_SSL_DEBUG_MSG( 1, ( "client only supports ssl smaller than minimum"
                             " [%d:%d] < [%d:%d]",
                             ssl->major_ver, ssl->minor_ver,
-                            ssl->conf->min_major_ver, ssl->conf->min_minor_ver ) );
+                            mbedtls_ssl_conf_get_min_major_ver( ssl->conf ),
+                            mbedtls_ssl_conf_get_min_minor_ver( ssl->conf ) ) );
 
         mbedtls_ssl_send_alert_message( ssl, MBEDTLS_SSL_ALERT_LEVEL_FATAL,
                                      MBEDTLS_SSL_ALERT_MSG_PROTOCOL_VERSION );
@@ -1213,7 +1215,8 @@
         {
             MBEDTLS_SSL_DEBUG_MSG( 3, ( "received FALLBACK_SCSV" ) );
 
-            if( ssl->minor_ver < ssl->conf->max_minor_ver )
+            if( ssl->minor_ver <
+                mbedtls_ssl_conf_get_max_minor_ver( ssl->conf ) )
             {
                 MBEDTLS_SSL_DEBUG_MSG( 1, ( "inapropriate fallback" ) );
 
@@ -1624,25 +1627,26 @@
     ssl->handshake->max_major_ver = ssl->major_ver;
     ssl->handshake->max_minor_ver = ssl->minor_ver;
 
-    if( ssl->major_ver < ssl->conf->min_major_ver ||
-        ssl->minor_ver < ssl->conf->min_minor_ver )
+    if( ssl->major_ver < mbedtls_ssl_conf_get_min_major_ver( ssl->conf ) ||
+        ssl->minor_ver < mbedtls_ssl_conf_get_min_minor_ver( ssl->conf ) )
     {
         MBEDTLS_SSL_DEBUG_MSG( 1, ( "client only supports ssl smaller than minimum"
                             " [%d:%d] < [%d:%d]",
                             ssl->major_ver, ssl->minor_ver,
-                            ssl->conf->min_major_ver, ssl->conf->min_minor_ver ) );
+                            mbedtls_ssl_conf_get_min_major_ver( ssl->conf ),
+                            mbedtls_ssl_conf_get_min_minor_ver( ssl->conf ) ) );
         mbedtls_ssl_send_alert_message( ssl, MBEDTLS_SSL_ALERT_LEVEL_FATAL,
                                      MBEDTLS_SSL_ALERT_MSG_PROTOCOL_VERSION );
         return( MBEDTLS_ERR_SSL_BAD_HS_PROTOCOL_VERSION );
     }
 
-    if( ssl->major_ver > ssl->conf->max_major_ver )
+    if( ssl->major_ver > mbedtls_ssl_conf_get_max_major_ver( ssl->conf ) )
     {
-        ssl->major_ver = ssl->conf->max_major_ver;
-        ssl->minor_ver = ssl->conf->max_minor_ver;
+        ssl->major_ver = mbedtls_ssl_conf_get_max_major_ver( ssl->conf );
+        ssl->minor_ver = mbedtls_ssl_conf_get_max_minor_ver( ssl->conf );
     }
-    else if( ssl->minor_ver > ssl->conf->max_minor_ver )
-        ssl->minor_ver = ssl->conf->max_minor_ver;
+    else if( ssl->minor_ver > mbedtls_ssl_conf_get_max_minor_ver( ssl->conf ) )
+        ssl->minor_ver = mbedtls_ssl_conf_get_max_minor_ver( ssl->conf );
 
     /*
      * Save client random (inc. Unix time)
@@ -2019,7 +2023,8 @@
         {
             MBEDTLS_SSL_DEBUG_MSG( 2, ( "received FALLBACK_SCSV" ) );
 
-            if( ssl->minor_ver < ssl->conf->max_minor_ver )
+            if( ssl->minor_ver <
+                mbedtls_ssl_conf_get_max_minor_ver( ssl->conf ) )
             {
                 MBEDTLS_SSL_DEBUG_MSG( 1, ( "inapropriate fallback" ) );