Refuse reproducible mode with MBEDTLS_USE_PSA_CRYPTO

With MBEDTLS_USE_PSA_CRYPTO, some of the randomness for the TLS
connection is generated inside the PSA crypto subsystem, which has no
reproducible mode. Whether there is a nonzero amount of randomness
coming from inside the PSA subsystem rather than from the random
generator set by mbedtls_ssl_conf_rng() depends on the choice of
cipher suite and other connection parameters as well as the level of
support for MBEDTLS_USE_PSA_CRYPTO. Rather than give unreliable
results, conservatively abort with a clear error message.

Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>

programs/ssl/ssl_test_lib.c

@@ -76,6 +76,14 @@ void rng_init( rng_context_t *rng )
 
 int rng_seed( rng_context_t *rng, int reproducible, const char *pers )
 {
+#if defined(MBEDTLS_USE_PSA_CRYPTO)
+    if( reproducible )
+    {
+        mbedtls_fprintf( stderr,
+                         "MBEDTLS_USE_PSA_CRYPTO does not support reproducible mode.\n" );
+        return( -1 );
+    }
+#endif
     int ( *f_entropy )( void *, unsigned char *, size_t ) =
         ( reproducible ? dummy_entropy : mbedtls_entropy_func );