mbedtls/tests/suites/test_suite_timing.function

/* BEGIN_HEADER */

/* This test module exercises the timing module. One of the expected failure
   modes is for timers to never expire, which could lead to an infinite loop.
   The function timing_timer_simple is protected against this failure mode and
   checks that timers do expire. Other functions will terminate if their
   timers do expire. Therefore it is recommended to run timing_timer_simple
   first and run other test functions only if that timing_timer_simple
   succeeded. */

#include <limits.h>

#include "mbedtls/timing.h"

/* Wait this many milliseconds for a short timing test. This duration
   should be large enough that, in practice, if you read the timer
   value twice in a row, it won't have jumped by that much. */
#define TIMING_SHORT_TEST_MS 100

/* A loop that waits TIMING_SHORT_TEST_MS must not take more than this many
   iterations. This value needs to be large enough to accommodate fast
   platforms (e.g. at 4GHz and 10 cycles/iteration a CPU can run through 20
   million iterations in 50ms). The only motivation to keep this value low is
   to avoid having an infinite loop if the timer functions are not implemented
   correctly. Ideally this value should be based on the processor speed but we
   don't have this information! */
#define TIMING_SHORT_TEST_ITERATIONS_MAX 1e8

/* alarm(0) must fire in no longer than this amount of time. */
#define TIMING_ALARM_0_DELAY_MS TIMING_SHORT_TEST_MS

static int expected_delay_status( uint32_t int_ms, uint32_t fin_ms,
                                  unsigned long actual_ms )
{
    return( fin_ms == 0 ? -1 :
            actual_ms >= fin_ms ? 2 :
            actual_ms >= int_ms ? 1 :
            0 );
}

/* END_HEADER */

/* BEGIN_DEPENDENCIES
 * depends_on:MBEDTLS_TIMING_C
 * END_DEPENDENCIES
 */

/* BEGIN_CASE */
void timing_timer_simple( )
{
    struct mbedtls_timing_hr_time timer;
    unsigned long millis = 0;
    unsigned long new_millis = 0;
    unsigned long iterations = 0;
    /* Start the timer. */
    (void) mbedtls_timing_get_timer( &timer, 1 );
    /* Busy-wait loop for a few milliseconds. */
    do
    {
        new_millis = mbedtls_timing_get_timer( &timer, 0 );
        ++iterations;
        /* Check that the timer didn't go backwards */
        TEST_ASSERT( new_millis >= millis );
        millis = new_millis;
    }
    while( millis < TIMING_SHORT_TEST_MS &&
           iterations <= TIMING_SHORT_TEST_ITERATIONS_MAX );
    /* The wait duration should have been large enough for at least a
       few runs through the loop, even on the slowest realistic platform. */
    TEST_ASSERT( iterations >= 2 );
    /* The wait duration shouldn't have overflowed the iteration count. */
    TEST_ASSERT( iterations < TIMING_SHORT_TEST_ITERATIONS_MAX );
    return;

exit:
    /* No cleanup needed, but show some diagnostic iterations, because timing
       problems can be hard to reproduce. */
    mbedtls_fprintf( stdout, "  Finished with millis=%lu new_millis=%lu get(timer)<=%lu iterations=%lu\n",
                     millis, new_millis, mbedtls_timing_get_timer( &timer, 0 ),
                     iterations );
}
/* END_CASE */

/* BEGIN_CASE */
void timing_timer_reset( )
{
    struct mbedtls_timing_hr_time timer;
    unsigned long millis = 0;
    unsigned long iterations = 0;
    /* Start the timer. Timers are always reset to 0. */
    TEST_ASSERT( mbedtls_timing_get_timer( &timer, 1 ) == 0 );
    /* Busy-wait loop for a few milliseconds */
    do
    {
        ++iterations;
        millis = mbedtls_timing_get_timer( &timer, 0 );
    }
    while( millis < TIMING_SHORT_TEST_MS );

    /* Reset the timer and check that it has restarted. */
    TEST_ASSERT( mbedtls_timing_get_timer( &timer, 1 ) == 0 );
    /* Read the timer immediately after reset. It should be 0 or close
       to it. */
    TEST_ASSERT( mbedtls_timing_get_timer( &timer, 0 ) < TIMING_SHORT_TEST_MS );
    return;

exit:
    /* No cleanup needed, but show some diagnostic information, because timing
       problems can be hard to reproduce. */
    mbedtls_fprintf( stdout, "  Finished with millis=%lu get(timer)<=%lu iterations=%lu\n",
                     millis, mbedtls_timing_get_timer( &timer, 0 ),
                     iterations );
}
/* END_CASE */

/* BEGIN_CASE */
void timing_two_timers( int delta )
{
    struct mbedtls_timing_hr_time timer1, timer2;
    unsigned long millis1, millis2;

    /* Start the first timer and wait for a short time. */
    (void) mbedtls_timing_get_timer( &timer1, 1 );
    do
    {
        millis1 = mbedtls_timing_get_timer( &timer1, 0 );
    }
    while( millis1 < TIMING_SHORT_TEST_MS );

    /* Do a short busy-wait, so that the difference between timer1 and timer2
       doesn't practically always end up being very close to a whole number of
       milliseconds. */
    while( delta > 0 )
        --delta;

    /* Start the second timer and compare it with the first. */
    mbedtls_timing_get_timer( &timer2, 1 );
    do
    {
        millis1 = mbedtls_timing_get_timer( &timer1, 0 );
        millis2 = mbedtls_timing_get_timer( &timer2, 0 );
        /* The first timer should always be ahead of the first. */
        TEST_ASSERT( millis1 > millis2 );
        /* The timers shouldn't drift apart, i.e. millis2-millis1 should stay
           roughly constant, but this is hard to test reliably, especially in
           a busy environment such as an overloaded continuous integration
           system, so we don't test it it. */
    }
    while( millis2 < TIMING_SHORT_TEST_MS );

    return;

exit:
    /* No cleanup needed, but show some diagnostic iterations, because timing
       problems can be hard to reproduce. */
    mbedtls_fprintf( stdout, "  Finished with millis1=%lu get(timer1)<=%lu millis2=%lu get(timer2)<=%lu\n",
                     millis1, mbedtls_timing_get_timer( &timer1, 0 ),
                     millis2, mbedtls_timing_get_timer( &timer2, 0 ) );
}
/* END_CASE */

/* BEGIN_CASE */
void timing_alarm( int seconds )
{
    struct mbedtls_timing_hr_time timer;
    unsigned long millis = 0;
    /* We check that about the desired number of seconds has elapsed. Be
       slightly liberal with the lower bound, so as to allow platforms where
       the alarm (with second resolution) and the timer (with millisecond
       resolution) are based on different clocks. Be very liberal with the
       upper bound, because the platform might be busy. */
    unsigned long millis_min = ( seconds > 0 ?
                                 seconds * 900 :
                                 0 );
    unsigned long millis_max = ( seconds > 0 ?
                                 seconds * 1100 + 400 :
                                 TIMING_ALARM_0_DELAY_MS );
    unsigned long iterations = 0;

    /* Set an alarm and count how long it takes with a timer. */
    (void) mbedtls_timing_get_timer( &timer, 1 );
    mbedtls_set_alarm( seconds );

    if( seconds > 0 )
    {
        /* We set the alarm for at least 1 second. It should not have fired
           immediately, even on a slow and busy platform. */
        TEST_ASSERT( !mbedtls_timing_alarmed );
    }
    /* A 0-second alarm should fire quickly, but we don't guarantee that it
       fires immediately, so mbedtls_timing_alarmed may or may not be set at
       this point. */

    /* Busy-wait until the alarm rings */
    do
    {
        ++iterations;
        millis = mbedtls_timing_get_timer( &timer, 0 );
    }
    while( !mbedtls_timing_alarmed && millis <= millis_max );

    TEST_ASSERT( mbedtls_timing_alarmed );
    TEST_ASSERT( millis >= millis_min );
    TEST_ASSERT( millis <= millis_max );

    mbedtls_timing_alarmed = 0;
    return;

exit:
    /* Show some diagnostic iterations, because timing
       problems can be hard to reproduce. */
    mbedtls_fprintf( stdout, "  Finished with alarmed=%d millis=%lu get(timer)<=%lu iterations=%lu\n",
                     mbedtls_timing_alarmed,
                     millis, mbedtls_timing_get_timer( &timer, 0 ),
                     iterations );
    /* Cleanup */
    mbedtls_timing_alarmed = 0;
}
/* END_CASE */

/* BEGIN_CASE */
void timing_delay( int int_ms, int fin_ms )
{
    /* This function assumes that if int_ms is nonzero then it is large
       enough that we have time to read all timers at least once in an
       interval of time lasting int_ms milliseconds, and likewise for (fin_ms
       - int_ms). So don't call it with arguments that are too small. */

    mbedtls_timing_delay_context delay;
    struct mbedtls_timing_hr_time timer;
    unsigned long delta; /* delay started between timer=0 and timer=delta */
    unsigned long before = 0, after = 0;
    unsigned long iterations = 0;
    int status = -2;
    int saw_status_1 = 0;
    int warn_inconclusive = 0;

    assert( int_ms >= 0 );
    assert( fin_ms >= 0 );

    /* Start a reference timer. Program a delay, and verify that the status of
       the delay is consistent with the time given by the reference timer. */
    (void) mbedtls_timing_get_timer( &timer, 1 );
    mbedtls_timing_set_delay( &delay, int_ms, fin_ms );
    /* Set delta to an upper bound for the interval between the start of timer
       and the start of delay. Reading timer after starting delay gives us an
       upper bound for the interval, rounded to a 1ms precision. Since this
       might have been rounded down, but we need an upper bound, we add 1. */
    delta = mbedtls_timing_get_timer( &timer, 0 ) + 1;

    status = mbedtls_timing_get_delay( &delay );
    if( fin_ms == 0 )
    {
        /* Cancelled timer. Just check the correct status for this case. */
        TEST_ASSERT( status == -1 );
        return;
    }

    /* Initially, none of the delays must be passed yet if they're nonzero.
       This could fail for very small values of int_ms and fin_ms, where "very
       small" depends how fast and how busy the platform is. */
    if( int_ms > 0 )
    {
        TEST_ASSERT( status == 0 );
    }
    else
    {
        TEST_ASSERT( status == 1 );
    }

    do
    {
        unsigned long delay_min, delay_max;
        int status_min, status_max;
        ++iterations;
        before = mbedtls_timing_get_timer( &timer, 0 );
        status = mbedtls_timing_get_delay( &delay );
        after = mbedtls_timing_get_timer( &timer, 0 );
        /* At a time between before and after, the delay's status was status.
           Check that this is consistent given that the delay was started
           between times 0 and delta. */
        delay_min = ( before > delta ? before - delta : 0 );
        status_min = expected_delay_status( int_ms, fin_ms, delay_min );
        delay_max = after;
        status_max = expected_delay_status( int_ms, fin_ms, delay_max );
        TEST_ASSERT( status >= status_min );
        TEST_ASSERT( status <= status_max );
        if( status == 1 )
            saw_status_1 = 1;
    }
    while ( before <= fin_ms + delta && status != 2 );

    /* Since we've waited at least fin_ms, the delay must have fully
       expired. */
    TEST_ASSERT( status == 2 );

    /* If the second delay is more than the first, then there must have been a
       point in time when the first delay was passed but not the second delay.
       This could fail for very small values of (fin_ms - int_ms), where "very
       small" depends how fast and how busy the platform is. In practice, this
       is the test that's most likely to fail on a heavily loaded machine. */
    if( fin_ms > int_ms )
    {
        warn_inconclusive = 1;
        TEST_ASSERT( saw_status_1 );
    }

    return;

exit:
    /* No cleanup needed, but show some diagnostic iterations, because timing
       problems can be hard to reproduce. */
    mbedtls_fprintf( stdout, "  Finished with delta=%lu before=%lu after=%lu status=%d iterations=%lu\n",
                     delta, before, after, status, iterations );
    if( warn_inconclusive )
        mbedtls_fprintf( stdout, "  Inconclusive test, try running it on a less heavily loaded machine.\n" );
 }
/* END_CASE */