Thank you Mike and Ard,

I'll definitely run ECC and resolve the code nits as well as the other suggestions.

So the previous RNG code in OpenSSL just had a 10-microsecond delay in between every 2 bytes. We could go back to that and match the behavior of before but as Mike pointed out, this approach suffers on systems with slow timer libs. I know this particular Rng library isn't meant to be a good source of randomness and it is meant to offer a solution to those who don't want to make the switch over to a good RngLib specifically for OpenSSL. That said, I don't see any reason why we can't make this a better source of random. I don't think it would be quite N, 2N, 3N, ... because of the variability in the delay mechanism but I do agree that it would be quite close to that. I'll throw out some options:

1. Implement a seeding mechanism that we mix in values with what we've previously generated. So that it's no longer N, 2N, 3N but rather some sort of hashing of the two numbers or other PRNG type system.
2. Use only 8 bits from the performance counter rather than 16. The idea here is that it would roll over more frequently and you'd be more subject to randomness. The downside is that this would take twice as long, which means to generate 64 bits of random data, it would take at least 12 performance timer ticks, which on systems where their performance counters run in KHz rather than MHz or GHz, means you could be looking at a delay of milliseconds rather than microseconds. I'd argue in that case that the platform should use a real RngLib rather than use this one if their timer is so slow, but that's beside the point.
3. Have some way of specifying the delay that is less deterministic? There are a few ways I can think of doing this but none are very good.I'm open to suggestions.

-Matthew Carlson


On Thu, Aug 20, 2020 at 8:21 AM Kinney, Michael D <michael.d.kinney@intel.com> wrote:
Hi Matt,

Some comments inline below.

I also see come comments from Ard on this series about code style.
I did not provide feedback on the code style issues here (except for
a function header comment block style).

There is a tool called ECC (EFI Code Checker) that is now enabled in
EDK II CI.  Please run this checker locally and resolve all issues in
your patch series.

Thanks,

Mike


> -----Original Message-----
> From: matthewfcarlson@gmail.com <matthewfcarlson@gmail.com>
> Sent: Wednesday, August 19, 2020 12:37 PM
> To: devel@edk2.groups.io
> Cc: Ard Biesheuvel <ard.biesheuvel@arm.com>; Kinney, Michael D <michael.d.kinney@intel.com>; Gao, Liming <liming.gao@intel.com>;
> Liu, Zhiguang <zhiguang.liu@intel.com>; Matthew Carlson <matthewfcarlson@gmail.com>
> Subject: [PATCH v8 1/5] MdePkg: TimerRngLib: Added RngLib that uses TimerLib
>
> From: Matthew Carlson <macarl@microsoft.com>
>
> Added a new RngLib that provides random numbers from the TimerLib
> using the performance counter. This is meant to be used for OpenSSL
> to replicate past behavior. This should not be used in production as
> a real source of entropy.
>
> Ref: https://github.com/tianocore/edk2/pull/845
> Ref: https://bugzilla.tianocore.org/show_bug.cgi?id=1871
>
> Cc: Ard Biesheuvel <ard.biesheuvel@arm.com>
> Cc: Michael D Kinney <michael.d.kinney@intel.com>
> Cc: Liming Gao <liming.gao@intel.com>
> Cc: Zhiguang Liu <zhiguang.liu@intel.com>
> Signed-off-by: Matthew Carlson <matthewfcarlson@gmail.com>
> ---
>  MdePkg/Library/BaseRngLibTimerLib/RngLibTimer.c          | 191 ++++++++++++++++++++
>  MdePkg/Library/BaseRngLibTimerLib/BaseRngLibTimerLib.inf |  36 ++++
>  MdePkg/Library/BaseRngLibTimerLib/BaseRngLibTimerLib.uni |  15 ++
>  MdePkg/MdePkg.dsc                                        |   3 +-
>  4 files changed, 244 insertions(+), 1 deletion(-)
>
> diff --git a/MdePkg/Library/BaseRngLibTimerLib/RngLibTimer.c b/MdePkg/Library/BaseRngLibTimerLib/RngLibTimer.c
> new file mode 100644
> index 000000000000..c72aa335823d
> --- /dev/null
> +++ b/MdePkg/Library/BaseRngLibTimerLib/RngLibTimer.c
> @@ -0,0 +1,191 @@
> +/** @file
>
> +  BaseRng Library that uses the TimerLib to provide reasonably random numbers.
>
> +  Do not use this on a production system.
>
> +
>
> +  Copyright (c) Microsoft Corporation.
>
> +  SPDX-License-Identifier: BSD-2-Clause-Patent
>
> +**/
>
> +
>
> +#include <Base.h>
>
> +#include <Library/BaseLib.h>
>
> +#include <Library/DebugLib.h>
>
> +#include <Library/TimerLib.h>
>
> +
>
> +/**
>
> + * Using the TimerLib GetPerformanceCounterProperties() we delay
>
> + * for enough time for the PerformanceCounter to increment.
>
> + * Depending on your system


Please update the comments to describe that this function returns
delay in microseconds.  It does not actually do the delay.

>
> + *
>
> + * If the return value from GetPerformanceCounterProperties (TimerLib)
>
> + * is zero, this function will not delay and attempt to assert.
>
> + */

Comment block style does not match EDK II style.  Remove extra '*'.


>
> +STATIC
>
> +UINT32
>
> +CalculateMinimumDecentDelayInMicroseconds (
>
> +  VOID
>
> +  )
>
> +{
>
> +  UINT64 StartValue;

Remove

>
> +  UINT64 EndValue;

Remove

>
> +  UINT64 CounterHz;
>
> +  UINT64 MinumumDelayInMicroSeconds;
>
> +
>
> +  // Get the counter properties
>
> +  CounterHz = GetPerformanceCounterProperties (&StartValue, &EndValue);


Change to:

    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;
>
> +  }
>
> +  // 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));
>
> +}
>
> +
>
> +
>
> +/**
>
> +  Generates a 16-bit random number.
>
> +
>
> +  if Rand is NULL, then ASSERT().
>
> +
>
> +  @param[out] Rand     Buffer pointer to store the 16-bit random value.
>
> +
>
> +  @retval TRUE         Random number generated successfully.
>
> +  @retval FALSE        Failed to generate the random number.
>
> +
>
> +**/
>
> +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 < 2; Index ++) {
>
> +    *RandPtr = (UINT8)(GetPerformanceCounter () & 0xFF);
>
> +    // Delay to give the performance counter a chance to change
>
> +    MicroSecondDelay (DelayInMicroSeconds);
>
> +    RandPtr++;
>
> +  }
>
> +  return TRUE;
>
> +}
>
> +
>
> +/**
>
> +  Generates a 32-bit random number.
>
> +
>
> +  if Rand is NULL, then ASSERT().
>
> +
>
> +  @param[out] Rand     Buffer pointer to store the 32-bit random value.
>
> +
>
> +  @retval TRUE         Random number generated successfully.
>
> +  @retval FALSE        Failed to generate the random number.
>
> +
>
> +**/
>
> +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 < 4; Index ++) {
>
> +    *RandPtr = (UINT8) (GetPerformanceCounter () & 0xFF);
>
> +    // Delay to give the performance counter a chance to change
>
> +    MicroSecondDelay (DelayInMicroSeconds);
>
> +    RandPtr++;
>
> +  }
>
> +  return TRUE;
>
> +}
>
> +
>
> +/**
>
> +  Generates a 64-bit random number.
>
> +
>
> +  if Rand is NULL, then ASSERT().
>
> +
>
> +  @param[out] Rand     Buffer pointer to store the 64-bit random value.
>
> +
>
> +  @retval TRUE         Random number generated successfully.
>
> +  @retval FALSE        Failed to generate the random number.
>
> +
>
> +**/
>
> +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 < 8; Index ++) {
>
> +    *RandPtr = (UINT8)(GetPerformanceCounter () & 0xFF);
>
> +    // Delay to give the performance counter a chance to change
>
> +    MicroSecondDelay (DelayInMicroSeconds);
>
> +    RandPtr++;
>
> +  }
>
> +
>
> +  return TRUE;
>
> +}
>
> +
>
> +/**
>
> +  Generates a 128-bit random number.
>
> +
>
> +  if Rand is NULL, then ASSERT().
>
> +
>
> +  @param[out] Rand     Buffer pointer to store the 128-bit random value.
>
> +
>
> +  @retval TRUE         Random number generated successfully.
>
> +  @retval FALSE        Failed to generate the random number.
>
> +
>
> +**/
>
> +BOOLEAN
>
> +EFIAPI
>
> +GetRandomNumber128 (
>
> +  OUT     UINT64                    *Rand
>
> +  )
>
> +{
>
> +  ASSERT (Rand != NULL);
>
> +  // This should take around 80ms


Update comment to remove mention of specific delay and match
similar comments in functions above.

>
> +
>
> +  // Read first 64 bits
>
> +  if (!GetRandomNumber64 (Rand)) {
>
> +    return FALSE;
>
> +  }
>
> +
>
> +  // Read second 64 bits
>
> +  return GetRandomNumber64 (++Rand);
>
> +}
>
> diff --git a/MdePkg/Library/BaseRngLibTimerLib/BaseRngLibTimerLib.inf b/MdePkg/Library/BaseRngLibTimerLib/BaseRngLibTimerLib.inf
> new file mode 100644
> index 000000000000..c499e5327351
> --- /dev/null
> +++ b/MdePkg/Library/BaseRngLibTimerLib/BaseRngLibTimerLib.inf
> @@ -0,0 +1,36 @@
> +## @file
>
> +#  Instance of RNG (Random Number Generator) Library.
>
> +#
>
> +#  BaseRng Library that uses the TimerLib to provide reasonably random numbers.
>
> +#  Do NOT use this on a production system as this uses the system performance
>
> +#  counter rather than a true source of random in addition to having a weak
>
> +#  random algorithm. This is provided primarily as a source of entropy for
>
> +#  OpenSSL for platforms that do not have a good built in RngLib as this
>
> +#  emulates what was done before (though it isn't perfect).
>
> +#
>
> +#  Copyright (c) Microsoft Corporation. All rights reserved.<BR>
>
> +#
>
> +#  SPDX-License-Identifier: BSD-2-Clause-Patent
>
> +#
>
> +#
>
> +##
>
> +
>
> +[Defines]
>
> +  INF_VERSION                    = 1.27
>
> +  BASE_NAME                      = BaseRngLibTimerLib
>
> +  MODULE_UNI_FILE                = BaseRngLibTimerLib.uni
>
> +  FILE_GUID                      = 74950C45-10FC-4AB5-B114-49C87C17409B
>
> +  MODULE_TYPE                    = BASE
>
> +  VERSION_STRING                 = 1.0
>
> +  LIBRARY_CLASS                  = RngLib
>
> +  CONSTRUCTOR                    = BaseRngLibConstructor
>
> +
>
> +[Sources]
>
> +  RngLibTimer.c
>
> +
>
> +[Packages]
>
> +  MdePkg/MdePkg.dec
>
> +
>
> +[LibraryClasses]
>
> +  BaseLib
>
> +  TimerLib
>
> diff --git a/MdePkg/Library/BaseRngLibTimerLib/BaseRngLibTimerLib.uni b/MdePkg/Library/BaseRngLibTimerLib/BaseRngLibTimerLib.uni
> new file mode 100644
> index 000000000000..fde24b9f0107
> --- /dev/null
> +++ b/MdePkg/Library/BaseRngLibTimerLib/BaseRngLibTimerLib.uni
> @@ -0,0 +1,15 @@
> +// @file
>
> +// Instance of RNG (Random Number Generator) Library.
>
> +//
>
> +// RngLib that uses TimerLib's performance counter to provide random numbers.
>
> +//
>
> +// Copyright (c) Microsoft Corporation.
>
> +//
>
> +// SPDX-License-Identifier: BSD-2-Clause-Patent
>
> +//
>
> +
>
> +
>
> +#string STR_MODULE_ABSTRACT     #language en-US "Instance of RNG Library"
>
> +
>
> +#string STR_MODULE_DESCRIPTION  #language en-US "BaseRng Library that uses the TimerLib to provide low-entropy random numbers"
>
> +
>
> diff --git a/MdePkg/MdePkg.dsc b/MdePkg/MdePkg.dsc
> index 472fa3777412..d7ba3a730909 100644
> --- a/MdePkg/MdePkg.dsc
> +++ b/MdePkg/MdePkg.dsc
> @@ -62,6 +62,8 @@
>    MdePkg/Library/BasePostCodeLibPort80/BasePostCodeLibPort80.inf
>
>    MdePkg/Library/BasePrintLib/BasePrintLib.inf
>
>    MdePkg/Library/BaseReportStatusCodeLibNull/BaseReportStatusCodeLibNull.inf
>
> +  MdePkg/Library/BaseRngLibTimerLib/BaseRngLibTimerLib.inf
>
> +  MdePkg/Library/BaseRngLibNull/BaseRngLibNull.inf
>
>    MdePkg/Library/BaseSerialPortLibNull/BaseSerialPortLibNull.inf
>
>    MdePkg/Library/BaseSynchronizationLib/BaseSynchronizationLib.inf
>
>    MdePkg/Library/BaseTimerLibNullTemplate/BaseTimerLibNullTemplate.inf
>
> @@ -69,7 +71,6 @@
>    MdePkg/Library/BaseUefiDecompressLib/BaseUefiTianoCustomDecompressLib.inf
>
>    MdePkg/Library/BaseSmbusLibNull/BaseSmbusLibNull.inf
>
>    MdePkg/Library/BaseSafeIntLib/BaseSafeIntLib.inf
>
> -  MdePkg/Library/BaseRngLibNull/BaseRngLibNull.inf
>
>
>
>    MdePkg/Library/DxeCoreEntryPoint/DxeCoreEntryPoint.inf
>
>    MdePkg/Library/DxeCoreHobLib/DxeCoreHobLib.inf
>
> --
> 2.28.0.windows.1