RngLibTimer.c

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#include <Base.h>
#include <Uefi.h>
#include <Library/BaseLib.h>
#include <Library/BaseMemoryLib.h>
#include <Library/DebugLib.h>
#include <Library/TimerLib.h>
#include <Guid/RngAlgorithm.h>
 
#define DEFAULT_DELAY_TIME_IN_MICROSECONDS  10
 
STATIC
UINT32
CalculateMinimumDecentDelayInMicroseconds (
  VOID
  )
{
  UINT64  CounterHz;
 
  // Get the counter properties
  CounterHz = GetPerformanceCounterProperties (NULL, NULL);
  // Make sure we won't divide by zero
  if (CounterHz == 0) {
    ASSERT (CounterHz != 0); // Assert so the developer knows something is wrong
    return DEFAULT_DELAY_TIME_IN_MICROSECONDS;
  }
 
  // Calculate the minimum delay based on 1.5 microseconds divided by the hertz.
  // We calculate the length of a cycle (1/CounterHz) and multiply it by 1.5 microseconds
  // This ensures that the performance counter has increased by at least one
  return (UINT32)(MAX (DivU64x64Remainder (1500000, CounterHz, NULL), 1));
}
 
BOOLEAN
EFIAPI
GetRandomNumber16 (
  OUT     UINT16  *Rand
  )
{
  UINT32  Index;
  UINT8   *RandPtr;
  UINT32  DelayInMicroSeconds;
 
  ASSERT (Rand != NULL);
 
  if (Rand == NULL) {
    return FALSE;
  }
 
  DelayInMicroSeconds = CalculateMinimumDecentDelayInMicroseconds ();
  RandPtr             = (UINT8 *)Rand;
  // Get 2 bytes of random ish data
  for (Index = 0; Index < sizeof (UINT16); Index++) {
    *RandPtr = (UINT8)(GetPerformanceCounter () & 0xFF);
    // Delay to give the performance counter a chance to change
    MicroSecondDelay (DelayInMicroSeconds);
    RandPtr++;
  }
 
  return TRUE;
}
 
BOOLEAN
EFIAPI
GetRandomNumber32 (
  OUT     UINT32  *Rand
  )
{
  UINT32  Index;
  UINT8   *RandPtr;
  UINT32  DelayInMicroSeconds;
 
  ASSERT (Rand != NULL);
 
  if (NULL == Rand) {
    return FALSE;
  }
 
  RandPtr             = (UINT8 *)Rand;
  DelayInMicroSeconds = CalculateMinimumDecentDelayInMicroseconds ();
  // Get 4 bytes of random ish data
  for (Index = 0; Index < sizeof (UINT32); Index++) {
    *RandPtr = (UINT8)(GetPerformanceCounter () & 0xFF);
    // Delay to give the performance counter a chance to change
    MicroSecondDelay (DelayInMicroSeconds);
    RandPtr++;
  }
 
  return TRUE;
}
 
BOOLEAN
EFIAPI
GetRandomNumber64 (
  OUT     UINT64  *Rand
  )
{
  UINT32  Index;
  UINT8   *RandPtr;
  UINT32  DelayInMicroSeconds;
 
  ASSERT (Rand != NULL);
 
  if (NULL == Rand) {
    return FALSE;
  }
 
  RandPtr             = (UINT8 *)Rand;
  DelayInMicroSeconds = CalculateMinimumDecentDelayInMicroseconds ();
  // Get 8 bytes of random ish data
  for (Index = 0; Index < sizeof (UINT64); Index++) {
    *RandPtr = (UINT8)(GetPerformanceCounter () & 0xFF);
    // Delay to give the performance counter a chance to change
    MicroSecondDelay (DelayInMicroSeconds);
    RandPtr++;
  }
 
  return TRUE;
}
 
BOOLEAN
EFIAPI
GetRandomNumber128 (
  OUT     UINT64  *Rand
  )
{
  ASSERT (Rand != NULL);
  // This should take around 80ms
 
  // Read first 64 bits
  if (!GetRandomNumber64 (Rand)) {
    return FALSE;
  }
 
  // Read second 64 bits
  return GetRandomNumber64 (++Rand);
}
 
EFI_STATUS
EFIAPI
GetRngGuid (
  GUID  *RngGuid
  )
{
  if (RngGuid == NULL) {
    return EFI_INVALID_PARAMETER;
  }
 
  CopyMem (RngGuid, &gEdkiiRngAlgorithmUnSafe, sizeof (*RngGuid));
  return EFI_SUCCESS;
}