fTPM/platform/Clock.c

/* Microsoft Reference Implementation for TPM 2.0
 *
 *  The copyright in this software is being made available under the BSD License,
 *  included below. This software may be subject to other third party and
 *  contributor rights, including patent rights, and no such rights are granted
 *  under this license.
 *
 *  Copyright (c) Microsoft Corporation
 *
 *  All rights reserved.
 *
 *  BSD License
 *
 *  Redistribution and use in source and binary forms, with or without modification,
 *  are permitted provided that the following conditions are met:
 *
 *  Redistributions of source code must retain the above copyright notice, this list
 *  of conditions and the following disclaimer.
 *
 *  Redistributions in binary form must reproduce the above copyright notice, this
 *  list of conditions and the following disclaimer in the documentation and/or
 *  other materials provided with the distribution.
 *
 *  THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS ""AS IS""
 *  AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 *  IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
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 *  (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
 *  SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */
//** Description
//
// This file contains the routines that are used by the simulator to mimic
// a hardware clock on a TPM.
//
// In this implementation, all the time values are measured in millisecond.
// However, the precision of the clock functions may be implementation dependent.

//** Includes and Data Definitions
#include "PlatformData.h"
#include "Platform_fp.h"
#include "TpmFail_fp.h"
#include <assert.h>
#include <tee_internal_api.h>

//** Simulator Functions
//*** Introduction
// This set of functions is intended to be called by the simulator environment in
// order to simulate hardware events.

//***_plat__TimerReset()
// This function sets current system clock time as t0 for counting TPM time.
// This function is called at a power on event to reset the clock. When the clock
// is reset, the indication that the clock was stopped is also set.
LIB_EXPORT void
_plat__TimerReset(
    void
    )
{
TEE_Result Result;
    TEE_Time Time = { 0 };

    // Reset our TA persistent time, this affects all instances.
    Result = TEE_SetTAPersistentTime(&Time);

    // Nothing we can do on failure here.
    assert(Result == TEE_SUCCESS);

    s_adjustRate = 0;
    s_lastSystemTime = 0;
    s_tpmTime = 0;
    s_adjustRate = CLOCK_NOMINAL;
    s_timerReset = TRUE;
    s_timerStopped = TRUE;

    return;
}

//*** _plat__TimerRestart()
// This function should be called in order to simulate the restart of the timer
// should it be stopped while power is still applied.
LIB_EXPORT void
_plat__TimerRestart(
    void
    )
{
    s_timerStopped = TRUE;
    return;
}

//** Functions Used by TPM
//*** Introduction
// These functions are called by the TPM code. They should be replaced by
// appropriated hardware functions.

#include <time.h>
TEE_Time     debugTime;

//*** _plat__RealTime()
// This is another, probably futile, attempt to define a portable function
// that will return a 64-bit clock value that has mSec resolution.
uint64_t
_plat__RealTime(
    void
)
{
    TEE_Result Result;
    TEE_Time Time;
    uint64_t Elapsed, Temp;

    Result = TEE_GetTAPersistentTime(&Time);

    // Error conditions from GetTime may be resolved with a clock reset
    if ((Result == TEE_ERROR_TIME_NOT_SET) ||
        (Result == TEE_ERROR_TIME_NEEDS_RESET)) {
        //
        // REVISIT: Since error conditions from get time may be resolved
        // by resetting time. Determine if, when this happens, we see
        // an issue with timing in the reference implementaiton.
        //
        _plat__TimerReset();

        Result = TEE_GetTAPersistentTime(&Time);
        // If the reset didn't resolve the error condision, give up.
        assert(Result == TEE_SUCCESS);
    }
    assert(Result == TEE_SUCCESS);

    Elapsed = ((Time.seconds * 1000) + (Time.millis));

    return Elapsed;
}

//***_plat__TimerRead()
// This function provides access to the tick timer of the platform. The TPM code
// uses this value to drive the TPM Clock.
//
// The tick timer is supposed to run when power is applied to the device. This timer
// should not be reset by time events including _TPM_Init. It should only be reset
// when TPM power is re-applied.
//
// If the TPM is run in a protected environment, that environment may provide the
// tick time to the TPM as long as the time provided by the environment is not
// allowed to go backwards. If the time provided by the system can go backwards
// during a power discontinuity, then the _plat__Signal_PowerOn should call
// _plat__TimerReset().
LIB_EXPORT uint64_t
_plat__TimerRead(
    void
    )
{
#ifdef HARDWARE_CLOCK
#error      "need a defintion for reading the hardware clock"
    return HARDWARE_CLOCK
#else
    clock64_t         timeDiff;
    clock64_t         adjustedTimeDiff;
    clock64_t         timeNow;
    clock64_t         readjustedTimeDiff;

    // This produces a timeNow that is basically locked to the system clock.
    timeNow = _plat__RealTime();

    // if this hasn't been initialized, initialize it
    if(s_lastSystemTime == 0)
    {
        s_lastSystemTime = timeNow;
        TEE_GetSystemTime(&debugTime);
        s_lastReportedTime = 0;
        s_realTimePrevious = 0;
    }
    // The system time can bounce around and that's OK as long as we don't allow
    // time to go backwards. When the time does appear to go backwards, set
    // lastSystemTime to be the new value and then update the reported time.
    if(timeNow < s_lastReportedTime)
        s_lastSystemTime = timeNow;
    s_lastReportedTime = s_lastReportedTime + timeNow - s_lastSystemTime;
    s_lastSystemTime = timeNow;
    timeNow = s_lastReportedTime;

    // The code above produces a timeNow that is similar to the value returned
    // by Clock(). The difference is that timeNow does not max out, and it is
    // at a ms. rate rather than at a CLOCKS_PER_SEC rate. The code below
    // uses that value and does the rate adjustment on the time value.
    // If there is no difference in time, then skip all the computations
    if(s_realTimePrevious >= timeNow)
        return s_tpmTime;
    // Compute the amount of time since the last update of the system clock
    timeDiff = timeNow - s_realTimePrevious;

    // Do the time rate adjustment and conversion from CLOCKS_PER_SEC to mSec
    adjustedTimeDiff = (timeDiff * CLOCK_NOMINAL) / ((uint64_t)s_adjustRate);

    // update the TPM time with the adjusted timeDiff
    s_tpmTime += (clock64_t)adjustedTimeDiff;

    // Might have some rounding error that would loose CLOCKS. See what is not
    // being used. As mentioned above, this could result in putting back more than
    // is taken out. Here, we are trying to recreate timeDiff.
    readjustedTimeDiff = (adjustedTimeDiff * (uint64_t)s_adjustRate )
                                / CLOCK_NOMINAL;

    // adjusted is now converted back to being the amount we should advance the
    // previous sampled time. It should always be less than or equal to timeDiff.
    // That is, we could not have use more time than we started with.
    s_realTimePrevious = s_realTimePrevious + readjustedTimeDiff;

#ifdef  DEBUGGING_TIME
    // Put this in so that TPM time will pass much faster than real time when
    // doing debug.
    // A value of 1000 for DEBUG_TIME_MULTIPLER will make each ms into a second
    // A good value might be 100
    return (s_tpmTime * DEBUG_TIME_MULTIPLIER);
#endif
    return s_tpmTime;
#endif
}


//*** _plat__TimerWasReset()
// This function is used to interrogate the flag indicating if the tick timer has
// been reset.
//
// If the resetFlag parameter is SET, then the flag will be CLEAR before the
// function returns.
LIB_EXPORT BOOL
_plat__TimerWasReset(
   void
    )
{
    BOOL         retVal = s_timerReset;
    s_timerReset = FALSE;
    return retVal;
}

//*** _plat__TimerWasStopped()
// This function is used to interrogate the flag indicating if the tick timer has
// been stopped. If so, this is typically a reason to roll the nonce.
//
// This function will CLEAR the s_timerStopped flag before returning. This provides
// functionality that is similar to status register that is cleared when read. This
// is the model used here because it is the one that has the most impact on the TPM
// code as the flag can only be accessed by one entity in the TPM. Any other
// implementation of the hardware can be made to look like a read-once register.
LIB_EXPORT BOOL
_plat__TimerWasStopped(
    void
    )
{
    BOOL         retVal = s_timerStopped;
    s_timerStopped = FALSE;
    return retVal;
}

//***_plat__ClockAdjustRate()
// Adjust the clock rate
LIB_EXPORT void
_plat__ClockAdjustRate(
    int              adjust         // IN: the adjust number.  It could be positive
                                    //     or negative
    )
{
    // We expect the caller should only use a fixed set of constant values to
    // adjust the rate
    switch(adjust)
    {
        case CLOCK_ADJUST_COARSE:
            s_adjustRate += CLOCK_ADJUST_COARSE;
            break;
        case -CLOCK_ADJUST_COARSE:
            s_adjustRate -= CLOCK_ADJUST_COARSE;
            break;
        case CLOCK_ADJUST_MEDIUM:
            s_adjustRate += CLOCK_ADJUST_MEDIUM;
            break;
        case -CLOCK_ADJUST_MEDIUM:
            s_adjustRate -= CLOCK_ADJUST_MEDIUM;
            break;
        case CLOCK_ADJUST_FINE:
            s_adjustRate += CLOCK_ADJUST_FINE;
            break;
        case -CLOCK_ADJUST_FINE:
            s_adjustRate -= CLOCK_ADJUST_FINE;
            break;
        default:
            // ignore any other values;
            break;
    }

    if(s_adjustRate > (CLOCK_NOMINAL + CLOCK_ADJUST_LIMIT))
        s_adjustRate = CLOCK_NOMINAL + CLOCK_ADJUST_LIMIT;
    if(s_adjustRate < (CLOCK_NOMINAL - CLOCK_ADJUST_LIMIT))
        s_adjustRate = CLOCK_NOMINAL - CLOCK_ADJUST_LIMIT;

    return;
}