Re: [PATCH] ArmPkg/ArmScmiDxe: Fix the calculation of RequiredArraySize in ClockDescribeRates()

["Sudeep Holla" <sudeep.holla@arm.com>]

On Fri, Feb 03, 2023 at 12:10:38PM +0100, Pierre Gondois wrote:
> Hello Sudeep,
> 
> On 2/2/23 15:30, Sudeep Holla wrote:
> > As per the SCMI specification, section CLOCK_DESCRIBE_RATES mentions that
> > the value of num_rates_flags[11:0] in the response must be 3 if the return
> > format is the triplet. Due to the buggy firmware, this was not noticed for
> > long time. The firmware is now fixed resulting in ClockDescribeRates() to
> > fail with "Buffer Too Small" error as the RequiredArraySize gets miscalculated
> > as 72 instead of 24.
> > 
> > Fix the issue by reusing the logic for both the return format which must
> > work if num_rates_flags has correct value as expected from the specification.
> > 
> > Cc: Pierre Gondois <Pierre.Gondois@arm.com>
> > Cc: Girish Pathak <girish.pathak@arm.com>
> > Cc: Jeff Brasen <jbrasen@nvidia.com>
> > Reported-by: Sami Mujawar <sami.mujawar@arm.com>
> > Signed-off-by: Sudeep Holla <sudeep.holla@arm.com>
> > ---
> >   ArmPkg/Drivers/ArmScmiDxe/ScmiClockProtocol.c | 7 +------
> >   1 file changed, 1 insertion(+), 6 deletions(-)
> > 
> > Hi All,
> > 
> > Sorry for the resend, I hadn't subscribed before so resending after the
> > subscription.
> > 
> > Regards,
> > Sudeep
> > 
> > diff --git a/ArmPkg/Drivers/ArmScmiDxe/ScmiClockProtocol.c b/ArmPkg/Drivers/ArmScmiDxe/ScmiClockProtocol.c
> > index 12a7e6df5d43..1412717bc227 100644
> > --- a/ArmPkg/Drivers/ArmScmiDxe/ScmiClockProtocol.c
> > +++ b/ArmPkg/Drivers/ArmScmiDxe/ScmiClockProtocol.c
> > @@ -236,12 +236,7 @@ ClockDescribeRates (
> >         *TotalRates = NUM_RATES (DescribeRates->NumRatesFlags)
> >                       + NUM_REMAIN_RATES (DescribeRates->NumRatesFlags);
> > -      if (*Format == ScmiClockRateFormatDiscrete) {
> > -        RequiredArraySize = (*TotalRates) * sizeof (UINT64);
> > -      } else {
> > -        // We need to return triplet of 64 bit value for each rate
> > -        RequiredArraySize = (*TotalRates) * 3 * sizeof (UINT64);
> > -      }
> > +      RequiredArraySize = (*TotalRates) * sizeof (UINT64);
> >         if (RequiredArraySize > (*RateArraySize)) {
> >           *RateArraySize = RequiredArraySize;
> 
> I think the following also needs to be modified:
> """
> for (RateNo = 0; RateNo < NUM_RATES (DescribeRates->NumRatesFlags); RateNo++) {
>   // Linear clock rates from minimum to maximum in steps
>   // Minimum clock rate.
>   Rate                                    = &DescribeRates->Rates[RateOffset++];
>   RateArray[RateIndex].ContinuousRate.Min =
> 	ConvertTo64Bit (Rate->Low, Rate->High);
> 
>   Rate = &DescribeRates->Rates[RateOffset++];
>   // Maximum clock rate.
>   RateArray[RateIndex].ContinuousRate.Max =
> 	ConvertTo64Bit (Rate->Low, Rate->High);
> 
>   Rate = &DescribeRates->Rates[RateOffset++];
>   // Step.
>   RateArray[RateIndex++].ContinuousRate.Step =
> 	ConvertTo64Bit (Rate->Low, Rate->High);
> }
> """
>

Right, good catch. For some reason, I don't see any exceptions in release
build :(. I will try the debug build and check. Thanks for the review.
> 
> With the above loop removed:
> Reviewed-by: Pierre Gondois <pierre.gondois@arm.com>
> Tested-by: Pierre Gondois <pierre.gondois@arm.com>
>

Thanks!

-- 
Regards,
Sudeep