From d39496233b5430be16c853f9bf8d7447c2ec86a6 Mon Sep 17 00:00:00 2001
From: Gilles Peskine <Gilles.Peskine@arm.com>
Date: Fri, 27 Oct 2017 18:42:32 +0200
Subject: [PATCH] Timing self test: increased duration

Increase the duration of the self test, otherwise it tends to fail on
a busy machine even with the recently upped tolerance. But run the
loop only once, it's enough for a simple smoke test.
---
 ChangeLog        |  2 ++
 library/timing.c | 30 ++++++++++++------------------
 2 files changed, 14 insertions(+), 18 deletions(-)

diff --git a/ChangeLog b/ChangeLog
index 9fd8cce093..c6031b4184 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -16,6 +16,8 @@ Features
    * Allow comments in test data files.
    * The selftest program can execute a subset of the tests based on command
      line arguments.
+   * Improve the timing self-tests to be more robust when run on a
+     heavily-loaded machine.
 
 Bugfix
    * Fix ssl_parse_record_header() to silently discard invalid DTLS records
diff --git a/library/timing.c b/library/timing.c
index 93e1826d9c..2c8d4bbbfa 100644
--- a/library/timing.c
+++ b/library/timing.c
@@ -439,28 +439,22 @@ int mbedtls_timing_self_test( int verbose )
     if( verbose != 0 )
         mbedtls_printf( "  TIMING test #2 (set/get_delay        ): " );
 
-    for( a = 200; a <= 400; a += 200 )
     {
-        for( b = 200; b <= 400; b += 200 )
-        {
-            mbedtls_timing_set_delay( &ctx, a, a + b );
+        a = 800;
+        b = 400;
+        mbedtls_timing_set_delay( &ctx, a, a + b );          /* T = 0 */
 
-            busy_msleep( a - a / 4 );
-            if( mbedtls_timing_get_delay( &ctx ) != 0 )
-                FAIL;
+        busy_msleep( a - a / 4 );                      /* T = a - a/4 */
+        if( mbedtls_timing_get_delay( &ctx ) != 0 )
+            FAIL;
 
-            busy_msleep( a / 2 );
-            if( mbedtls_timing_get_delay( &ctx ) != 1 )
-                FAIL;
+        busy_msleep( a / 4 + b / 4 );                  /* T = a + b/4 */
+        if( mbedtls_timing_get_delay( &ctx ) != 1 )
+            FAIL;
 
-            busy_msleep( b - a / 4 - b / 4 );
-            if( mbedtls_timing_get_delay( &ctx ) != 1 )
-                FAIL;
-
-            busy_msleep( b / 2 );
-            if( mbedtls_timing_get_delay( &ctx ) != 2 )
-                FAIL;
-        }
+        busy_msleep( b );                          /* T = a + b + b/4 */
+        if( mbedtls_timing_get_delay( &ctx ) != 2 )
+            FAIL;
     }
 
     mbedtls_timing_set_delay( &ctx, 0, 0 );