Re: [edk2-devel] [PATCH edk2-platforms 1/1] SbsaQemu: use FEAT_RNG for EFI_RNG_PROTOCOL

["Leif Lindholm" <quic_llindhol@quicinc.com>]

On 2024-07-01 13:58, Marcin Juszkiewicz wrote:

>>> diff --git a/Platform/Qemu/SbsaQemu/SbsaQemu.dsc 
>>> b/Platform/Qemu/SbsaQemu/SbsaQemu.dsc
>>> index 9306986bf7c0..3463e5c7a635 100644
>>> --- a/Platform/Qemu/SbsaQemu/SbsaQemu.dsc
>>> +++ b/Platform/Qemu/SbsaQemu/SbsaQemu.dsc
>>> @@ -148,7 +148,9 @@ [LibraryClasses.common]
>>>     #
>>
>> Since sbsa-ref still supports processors without FEAT_RNG, this may 
>> cause unexpected breakages for some users.
> 
> That's why I sent it as more of RFC than changes for merging.
> 
>> Could we first of all conditionalise this change:
>>
>> [Defines]
>> ...
>>    DEFINE_DEBUG_PRINT_ERROR_LEVEL = ...
>>    DEFINE FEATRNG_ENABLE         = TRUE
>>
>> so that someone who still wishes to run tests against older cpus can 
>> still do so through a rebuild with -D FEATRNG_ENABLE=FALSE
> 
> Is there a way to load both BaseRngLib and BaseRngLibTimerLib and switch
> between them depending on availability of FEAT_RNG?

Not without severe hackery. The library is statically linked into RngDxe.

>>> diff --git a/Platform/Qemu/SbsaQemu/SbsaQemu.fdf 
>>> b/Platform/Qemu/SbsaQemu/SbsaQemu.fdf
>>> index b35f42e11aa4..51a1ef8519f9 100644
>>> --- a/Platform/Qemu/SbsaQemu/SbsaQemu.fdf
>>> +++ b/Platform/Qemu/SbsaQemu/SbsaQemu.fdf
>>> @@ -192,6 +192,7 @@ [FV.FvMain]
>>>     INF ArmPkg/Drivers/TimerDxe/TimerDxe.inf
>>>     INF OvmfPkg/VirtNorFlashDxe/VirtNorFlashDxe.inf
>>>     INF MdeModulePkg/Universal/WatchdogTimerDxe/WatchdogTimer.inf
>>> +  INF SecurityPkg/RandomNumberGenerator/RngDxe/RngDxe.inf
>>
>> Second:
>> What is the failure mode of running the BaseRngLib flavour on cpus 
>> that don't support FEAT_RNG? RngDxe itself seems to do the right 
>> thing, but do we get any warning messages or will certain operations 
>> now fail silently?
> 
> On FEAT_RNG cores we get:
> 
> InstallProtocolInterface: BC62157E-3E33-4FEC-9920-2D3B36D750DF 101FAD68798
> ProtectUefiImageCommon - 0xFAD683C0
>    - 0x00000101FBBDB000 - 0x0000000000007000
> ArmTrngLib could not be correctly initialized.
> InstallProtocolInterface: 3152BCA5-EADE-433D-862E-C01CDC291F44 101FBBE0020
> Loading driver B601F8C4-43B7-4784-95B1-F4226CB40CEE
> 
> 
> On core without FEAT_RNG:
> 
> InstallProtocolInterface: BC62157E-3E33-4FEC-9920-2D3B36D750DF 101FAD68798
> ProtectUefiImageCommon - 0xFAD683C0
>    - 0x00000101FBBDB000 - 0x0000000000007000
> ArmTrngLib could not be correctly initialized.
> Error: Image at 101FBBDB000 start failed: 00000001
> Loading driver B601F8C4-43B7-4784-95B1-F4226CB40CEE

But it still keeps booting correctly after that? With some missing 
functionality?

> So there is some kind of information but you need to know what
> to look for ;(

Ard: would you be opposed to putting a DEBUG print and/or an ASSERT in 
BaseRngLibContructor if mRndrSupported == 0?

An alternative would be to place a test and noisy warning inside 
SbsaQemuPlatformDxe.

/
     Leif



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