Improve implementation of Mbed TLS timing

TESTS/configs/mbedtls.json

@@ -0,0 +1,7 @@
+{
+    "macros": [
+        "MBEDTLS_SELF_TEST",
+        "MBEDTLS_TIMING_C",
+        "MBEDTLS_TIMING_ALT"
+    ]
+}

connectivity/mbedtls/include/mbedtls/config-no-entropy.h

@@ -48,7 +48,7 @@
 #define MBEDTLS_PK_RSA_ALT_SUPPORT
 #define MBEDTLS_PKCS1_V15
 #define MBEDTLS_PKCS1_V21
-#define MBEDTLS_SELF_TEST
+//#define MBEDTLS_SELF_TEST
 #define MBEDTLS_VERSION_FEATURES
 #define MBEDTLS_X509_CHECK_KEY_USAGE
 #define MBEDTLS_X509_CHECK_EXTENDED_KEY_USAGE

connectivity/mbedtls/include/mbedtls/config.h

@@ -1396,7 +1396,7 @@
  *
  * Enable the checkup functions (*_self_test).
  */
-#define MBEDTLS_SELF_TEST
+//#define MBEDTLS_SELF_TEST
 
 /**
  * \def MBEDTLS_SHA256_SMALLER

connectivity/mbedtls/platform/inc/timing_alt.h

@@ -24,11 +24,9 @@
 #include "mbedtls/timing.h"
 #if defined(MBEDTLS_TIMING_ALT)
 
-#include <time.h>
-
 struct mbedtls_timing_hr_time
 {
-    struct timeval start;
+    unsigned long start;
 };
 
 typedef struct mbedtls_timing_delay_context

connectivity/mbedtls/platform/src/timing_mbed.cpp

@@ -1,6 +1,7 @@
 /*
  *  timing.cpp
  *
+ *  Copyright The Mbed TLS Contributors
  *  Copyright (C) 2021, Arm Limited, All Rights Reserved
  *  SPDX-License-Identifier: Apache-2.0
  *
@@ -23,8 +24,14 @@
 #else
 #include MBEDTLS_CONFIG_FILE
 #endif
+
+#if defined(MBEDTLS_TIMING_ALT)
+
 #include "mbedtls/timing.h"
 #include "drivers/Timeout.h"
+#include "drivers/LowPowerTimeout.h"
+#include "drivers/Timer.h"
+#include "drivers/LowPowerTimer.h"
 #include <chrono>
 
 extern "C" {
@@ -38,30 +45,101 @@ static void handle_alarm(void)
 
 extern "C" void mbedtls_set_alarm(int seconds)
 {
+#if DEVICE_LPTICKER
+    static mbed::LowPowerTimeout t;
+#elif DEVICE_USTICKER
     static mbed::Timeout t;
+#else
+#error "MBEDTLS_TIMING_C requires either LPTICKER or USTICKER"
+#endif
+
     mbedtls_timing_alarmed = 0;
 
     t.attach(handle_alarm, std::chrono::seconds(seconds));
 }
 
+// The static Mbed timer here is initialized once only.
+// Mbed TLS can have multiple timers (mbedtls_timing_hr_time) derived
+// from the Mbed timer.
+#if DEVICE_LPTICKER
+static mbed::LowPowerTimer timer;
+#elif DEVICE_USTICKER
+static mbed::Timer timer;
+#else
+#error "MBEDTLS_TIMING_C requires either LPTICKER or USTICKER"
+#endif
+static int timer_init = 0;
+
 #if !defined(HAVE_HARDCLOCK)
 #define HAVE_HARDCLOCK
-#include "platform/mbed_rtc_time.h"
-static int hardclock_init = 0;
-static struct timeval tv_init;
 
 extern "C" unsigned long mbedtls_timing_hardclock(void)
 {
-    struct timeval tv_cur;
-
-    if (hardclock_init == 0)
-    {
-        gettimeofday(&tv_init, NULL);
-        hardclock_init = 1;
+    if (timer_init == 0) {
+        timer.reset();
+        timer.start();
+        timer_init = 1;
     }
 
-    gettimeofday(&tv_cur, NULL);
-    return((tv_cur.tv_sec - tv_init.tv_sec) * 1000000
-          + (tv_cur.tv_usec - tv_init.tv_usec));
+    return timer.elapsed_time().count();
 }
 #endif /* !HAVE_HARDCLOCK */
+
+extern "C" unsigned long mbedtls_timing_get_timer(struct mbedtls_timing_hr_time *val, int reset)
+{
+    if (timer_init == 0) {
+        timer.reset();
+        timer.start();
+        timer_init = 1;
+    }
+
+    if (reset) {
+        val->start = std::chrono::duration_cast<std::chrono::milliseconds>(timer.elapsed_time()).count();
+        return 0;
+    } else {
+        return std::chrono::duration_cast<std::chrono::milliseconds>(timer.elapsed_time()).count() - val->start;
+    }
+}
+
+/**
+ * Note: The following implementations come from the default timing.c
+ * from Mbed TLS. They are disabled in timing.c when MBEDTLS_TIMING_ALT
+ * is defined, but the implementation is nonetheless applicable to
+ * Mbed OS, so we copy them over.
+ */
+
+extern "C" void mbedtls_timing_set_delay(void *data, uint32_t int_ms, uint32_t fin_ms)
+{
+    mbedtls_timing_delay_context *ctx = (mbedtls_timing_delay_context *) data;
+
+    ctx->int_ms = int_ms;
+    ctx->fin_ms = fin_ms;
+
+    if (fin_ms != 0) {
+        (void) mbedtls_timing_get_timer(&ctx->timer, 1);
+    }
+}
+
+extern "C" int mbedtls_timing_get_delay(void *data)
+{
+    mbedtls_timing_delay_context *ctx = (mbedtls_timing_delay_context *) data;
+    unsigned long elapsed_ms;
+
+    if (ctx->fin_ms == 0) {
+        return -1;
+    }
+
+    elapsed_ms = mbedtls_timing_get_timer(&ctx->timer, 0);
+
+    if (elapsed_ms >= ctx->fin_ms) {
+        return 2;
+    }
+
+    if (elapsed_ms >= ctx->int_ms) {
+        return 1;
+    }
+
+    return 0;
+}
+
+#endif // MBEDTLS_TIMING_ALT

connectivity/mbedtls/tests/TESTS/mbedtls/selftest/main.cpp

@@ -31,10 +31,15 @@ using namespace utest::v1;
 #include MBEDTLS_CONFIG_FILE
 #endif
 
+#if !defined(MBEDTLS_SELF_TEST)
+#error [NOT_SUPPORTED] MBEDTLS_SELF_TEST undefined
+#endif
+
 #include "mbedtls/sha256.h"
 #include "mbedtls/sha512.h"
 #include "mbedtls/entropy.h"
 #include "mbedtls/entropy_poll.h"
+#include "mbedtls/timing.h"
 
 #include <string.h>
 
@@ -65,6 +70,10 @@ MBEDTLS_SELF_TEST_TEST_CASE(mbedtls_sha512_self_test)
 MBEDTLS_SELF_TEST_TEST_CASE(mbedtls_entropy_self_test)
 #endif
 
+#if defined(MBEDTLS_TIMING_C)
+MBEDTLS_SELF_TEST_TEST_CASE(mbedtls_timing_self_test)
+#endif
+
 #else
 #warning "MBEDTLS_SELF_TEST not enabled"
 #endif /* MBEDTLS_SELF_TEST */
@@ -84,6 +93,10 @@ Case cases[] = {
     Case("mbedtls_entropy_self_test", mbedtls_entropy_self_test_test_case),
 #endif
 
+#if defined(MBEDTLS_TIMING_C)
+    Case("mbedtls_timing_self_test", mbedtls_timing_self_test_test_case),
+#endif
+
 #endif /* MBEDTLS_SELF_TEST */
 };
 

connectivity/mbedtls/tools/importer/adjust-config.sh

@@ -117,6 +117,9 @@ conf unset MBEDTLS_SSL_TRUNCATED_HMAC
 
 conf unset MBEDTLS_PLATFORM_TIME_TYPE_MACRO
 
+# potentially save flash space by not enabling self-tests by default
+conf unset MBEDTLS_SELF_TEST
+
 # The default size of MBEDTLS_MPI_MAX_SIZE is 1024 bytes.
 # In some cases, this value is set to stack buffers.
 # Reduce the maximal MBEDTLS_MPI_MAX_SIZE to 512 bytes,

connectivity/mbedtls/tools/importer/adjust-no-entropy-config.sh

@@ -37,3 +37,6 @@ add_code() {
 
 conf set MBEDTLS_CMAC_C
 conf unset MBEDTLS_CIPHER_MODE_XTS
+
+# potentially save flash space by not enabling self-tests by default
+conf unset MBEDTLS_SELF_TEST