Squashed commit upgrading to mbedtls-2.28.1

Squash merging branch import/mbedtls-2.28.1

 ebf1f6a58089 ("libmbedtls: compile new files added with 2.28.1")
 3ffb51b58a54 ("libmbedtls: add SM2 curve")
 c425755720b4 ("libmbedtls: mbedtls_mpi_exp_mod(): optimize mempool usage")
 23493c822a82 ("libmbedtls: mbedtls_mpi_exp_mod(): reduce stack usage")
 dcdca2348dff ("libmbedtls: mbedtls_mpi_exp_mod() initialize W")
 dc2994976958 ("libmbedtls: fix no CRT issue")
 c6628873b281 ("libmbedtls: add interfaces in mbedtls for context memory operation")
 8acd202d3e55 ("libmedtls: mpi_miller_rabin: increase count limit")
 37284e28d5d9 ("libmbedtls: add mbedtls_mpi_init_mempool()")
 b499a75f29f3 ("libmbedtls: make mbedtls_mpi_mont*() available")
 2080a8c96a5d ("mbedtls: configure mbedtls to reach for config")
 e0858334327a ("mbedtls: remove default include/mbedtls/config.h")
 dd9688e6b8ce ("Import mbedtls-2.28.1")

Signed-off-by: Jerome Forissier <jerome.forissier@linaro.org>
Acked-by: Jens Wiklander <jens.wiklander@linaro.org>
diff --git a/lib/libmbedtls/mbedtls/library/ssl_cookie.c b/lib/libmbedtls/mbedtls/library/ssl_cookie.c
index 69d1b32..3781796 100644
--- a/lib/libmbedtls/mbedtls/library/ssl_cookie.c
+++ b/lib/libmbedtls/mbedtls/library/ssl_cookie.c
@@ -36,6 +36,7 @@
 #include "mbedtls/ssl_internal.h"
 #include "mbedtls/error.h"
 #include "mbedtls/platform_util.h"
+#include "mbedtls/constant_time.h"
 
 #include <string.h>
 
@@ -62,7 +63,7 @@
 
 /*
  * Cookies are formed of a 4-bytes timestamp (or serial number) and
- * an HMAC of timestemp and client ID.
+ * an HMAC of timestamp and client ID.
  */
 #define COOKIE_LEN      ( 4 + COOKIE_HMAC_LEN )
 
@@ -121,6 +122,7 @@
 /*
  * Generate the HMAC part of a cookie
  */
+MBEDTLS_CHECK_RETURN_CRITICAL
 static int ssl_cookie_hmac( mbedtls_md_context_t *hmac_ctx,
                             const unsigned char time[4],
                             unsigned char **p, unsigned char *end,
@@ -166,10 +168,7 @@
     t = ctx->serial++;
 #endif
 
-    (*p)[0] = (unsigned char)( t >> 24 );
-    (*p)[1] = (unsigned char)( t >> 16 );
-    (*p)[2] = (unsigned char)( t >>  8 );
-    (*p)[3] = (unsigned char)( t       );
+    MBEDTLS_PUT_UINT32_BE(t, *p, 0);
     *p += 4;
 
 #if defined(MBEDTLS_THREADING_C)
@@ -220,15 +219,20 @@
 
 #if defined(MBEDTLS_THREADING_C)
     if( mbedtls_mutex_unlock( &ctx->mutex ) != 0 )
-        return( MBEDTLS_ERROR_ADD( MBEDTLS_ERR_SSL_INTERNAL_ERROR,
-                MBEDTLS_ERR_THREADING_MUTEX_ERROR ) );
+    {
+        ret = MBEDTLS_ERROR_ADD( MBEDTLS_ERR_SSL_INTERNAL_ERROR,
+                                 MBEDTLS_ERR_THREADING_MUTEX_ERROR );
+    }
 #endif
 
     if( ret != 0 )
-        return( ret );
+        goto exit;
 
-    if( mbedtls_ssl_safer_memcmp( cookie + 4, ref_hmac, sizeof( ref_hmac ) ) != 0 )
-        return( -1 );
+    if( mbedtls_ct_memcmp( cookie + 4, ref_hmac, sizeof( ref_hmac ) ) != 0 )
+    {
+        ret = -1;
+        goto exit;
+    }
 
 #if defined(MBEDTLS_HAVE_TIME)
     cur_time = (unsigned long) mbedtls_time( NULL );
@@ -242,8 +246,13 @@
                   ( (unsigned long) cookie[3]       );
 
     if( ctx->timeout != 0 && cur_time - cookie_time > ctx->timeout )
-        return( -1 );
+    {
+        ret = -1;
+        goto exit;
+    }
 
-    return( 0 );
+exit:
+    mbedtls_platform_zeroize( ref_hmac, sizeof( ref_hmac ) );
+    return( ret );
 }
 #endif /* MBEDTLS_SSL_COOKIE_C */