Re: [Patch] UefiCpuPkg/MpLib: fix potential overflow issue.

["Kinney, Michael D" <michael.d.kinney@intel.com>]

Hi Eric,

With this patch GetPerformanceCounterProperties() is called 
twice.  I think you can use TimestampCounterFreq in the else
clause.

Also, the comment blocks are no longer correct.  The original
comment block goes with the else clause, and you need a new
comment block for the if statement that describes the check
for an overflow.

Mike

> -----Original Message-----
> From: Dong, Eric
> Sent: Tuesday, August 22, 2017 10:30 PM
> To: edk2-devel@lists.01.org
> Cc: Kinney, Michael D <michael.d.kinney@intel.com>; Ni, Ruiyu
> <ruiyu.ni@intel.com>
> Subject: [Patch] UefiCpuPkg/MpLib: fix potential overflow
> issue.
> 
> Current calculate timeout logic may have overflow if the input
> timeout value too large. This patch fix this potential overflow
> issue.
> 
> Cc: Michael Kinney <michael.d.kinney@intel.com>
> Cc: Ruiyu Ni <ruiyu.ni@intel.com>
> Contributed-under: TianoCore Contribution Agreement 1.1
> Signed-off-by: Eric Dong <eric.dong@intel.com>
> ---
>  UefiCpuPkg/Library/MpInitLib/MpLib.c | 30
> +++++++++++++++++++++++-------
>  1 file changed, 23 insertions(+), 7 deletions(-)
> 
> diff --git a/UefiCpuPkg/Library/MpInitLib/MpLib.c
> b/UefiCpuPkg/Library/MpInitLib/MpLib.c
> index ed1f55e..005dec4 100644
> --- a/UefiCpuPkg/Library/MpInitLib/MpLib.c
> +++ b/UefiCpuPkg/Library/MpInitLib/MpLib.c
> @@ -1001,6 +1001,9 @@ CalculateTimeout (
>    OUT UINT64  *CurrentTime
>    )
>  {
> +  UINT64 TimeoutInSeconds;
> +  UINT64 TimestampCounterFreq;
> +
>    //
>    // Read the current value of the performance counter
>    //
> @@ -1019,13 +1022,26 @@ CalculateTimeout (
>    // in Hz. So multiply the return value with
> TimeoutInMicroseconds and then divide
>    // it by 1,000,000, to get the number of ticks for the
> timeout value.
>    //
> -  return DivU64x32 (
> -           MultU64x64 (
> -             GetPerformanceCounterProperties (NULL, NULL),
> -             TimeoutInMicroseconds
> -             ),
> -           1000000
> -           );
> +  TimestampCounterFreq = GetPerformanceCounterProperties
> (NULL, NULL);
> +  if (DivU64x64Remainder (MAX_UINT64, TimeoutInMicroseconds,
> NULL) < TimestampCounterFreq) {
> +    //
> +    // Convert microseconds into seconds if direct
> multiplication overflows
> +    //
> +    TimeoutInSeconds = DivU64x32 (TimeoutInMicroseconds,
> 1000000);
> +    //
> +    // Assertion if the final tick count exceeds MAX_UINT64
> +    //
> +    ASSERT (DivU64x64Remainder (MAX_UINT64, TimeoutInSeconds,
> NULL) >= TimestampCounterFreq);
> +    return MultU64x64 (TimestampCounterFreq,
> TimeoutInSeconds);
> +  } else {
> +    return DivU64x32 (
> +             MultU64x64 (
> +               GetPerformanceCounterProperties (NULL, NULL),

Use TimestampCounterFreq instead.

> +               TimeoutInMicroseconds
> +               ),
> +             1000000
> +             );
> +  }
>  }
> 
>  /**
> --
> 2.7.0.windows.1