Re: Question About DxeDriver load process

[Andrew Fish <afish@apple.com>]

Rafael,

I forgot to mention that the DXE Core is loaded by the DXE IPL PEIM. This can sometime require the discovery of a new FV to find the DXE Core. 
https://github.com/tianocore/edk2/blob/master/MdeModulePkg/Core/DxeIplPeim/DxeLoad.c#L254

Thanks,

Andrew Fish

> On Jul 30, 2018, at 4:46 AM, Rafael Machado <rafaelrodrigues.machado@gmail.com> wrote:
> 
> Hi Andrew
> 
> Thanks a lot for the perfectly detailed explanation!
> Amazing!
> 
> Thanks and Regards
> Rafael R. Machado
> 
> Em sex, 27 de jul de 2018 às 19:14, Andrew Fish <afish@apple.com> escreveu:
> 
>> Rafael,
>> 
>> Since it is useful to also understand this when you are bringing up a
>> platform....
>> 
>> SEC generally contains the hardware reset vector. SEC hands off to the PEI
>> Core. Generally there is some build magic to help SEC find the PEI Core.
>> Worst case you can walk the BFV (Boot Firmware Volume) and find it.
>> 
>> SEC hands the PEI Core the EFI_SEC_PEI_HAND_OFF structure. This is how the
>> PEI Core knows about stack, heap, and the location of the BFV to find PEIMs
>> 
>> https://github.com/tianocore/edk2/blob/master/MdePkg/Include/Pi/PiPeiCis.h#L967
>> 
>> The PEI Core has a PPI Notify Callback for
>> gEfiPeiFirmwareVolumeInfoPpiGuid, and  gEfiPeiFirmwareVolumeInfo2PpiGuid to
>> discover new FVs.
>> 
>> https://github.com/tianocore/edk2/blob/master/MdeModulePkg/Core/Pei/FwVol/FwVol.c#L547
>> 
>> PEI Code writes hobs, EFI_HOB_TYPE_FV and EFI_HOB_TYPE_FV3, to help DXE
>> discover FVs.
>> 
>> When the DXE Core is started it will call FwVolBlockDriverInit() and  all
>> the EFI_HOB_TYPE_FV, and optionally pick up the authentication status from
>> EFI_HOB_TYPE_FV3, will get processed.
>> 
>> https://github.com/tianocore/edk2/blob/master/MdeModulePkg/Core/Dxe/FwVolBlock/FwVolBlock.c#L625
>> 
>> via calling ProduceFVBProtocolOnBuffer(). ProduceFVBProtocolOnBuffer() can
>> also be called gBS->ProcessFirmwareVolume().
>> 
>> https://github.com/tianocore/edk2/blob/master/MdeModulePkg/Core/Dxe/FwVolBlock/FwVolBlock.c#L452
>> 
>> https://github.com/tianocore/edk2/blob/master/MdeModulePkg/Core/Dxe/FwVolBlock/FwVolBlock.c#L687
>> 
>> Loading drivers from the FV is the job of the DXE Dispatcher. The DXE
>> Dispatcher has protocol notify event on gEfiFirmwareVolume2ProtocolGuid
>> that will get the executables in the Dispatch list, mDiscoveredList.
>> 
>> https://github.com/tianocore/edk2/blob/master/MdeModulePkg/Core/Dxe/Dispatcher/Dispatcher.c#L1193
>> 
>> So adding a gEfiFirmwareVolume2ProtocolGuid driver, or calling
>> gBS->ProcessFirmwareVolume() is how you would make an FV show up that was
>> not listed in the HOBs.
>> 
>> In the DXE Phase security is handle by gBS->LoadImage() and it uses
>> gEfiSecurity2ArchProtocolGuid and gEfiSecurityArchProtocolGuid to validate
>> the image. This makes sense as a signed EFI PE/COFF image has the signature
>> in the PE/COFF image, so you have to start the PE/COFF loading process to
>> verify that signature.  gEfiSecurity2ArchProtocolGuid lets you build
>> security policy based on the location of the driver.
>> 
>> https://github.com/tianocore/edk2/blob/master/MdeModulePkg/Core/Dxe/Image/Image.c#L1041
>> 
>> When the Dispatcher runs of things to Dispatch it returns and the DXE Core
>> calls the BDS to process platform Boot Device Selection.
>> 
>> https://github.com/tianocore/edk2/blob/master/MdeModulePkg/Core/Dxe/DxeMain/DxeMain.c#L550
>> 
>> After BDS starts the only way to run code from an FV would be to call
>> gDS->Dispatcher(). Likely you would call gDS->ProcessFirmwareVolume() and
>> then  gDS->Dispatcher(). To speed boot it is not uncommon to have multiple
>> FVs. For example you could have an FV that contained all the setup
>> resources and only call gDS->ProcessFirmwareVolume() on that FV if the user
>> hit the Setup hot key.
>> 
>> Thanks,
>> 
>> Andrew Fish
>> 
>> PS For x86 (0xFFFFFFF0 reset vector) and any other architectures that have
>> the reset vector at the end there is a special file name in the FV called
>> gEfiFirmwareVolumeTopFileGuid that tells the FV creation tools to put that
>> file at the very end of the FV, so the end of that file would end up at the
>> reset vector location.
>> 
>> 
>>> On Jul 27, 2018, at 11:12 AM, Rafael Machado <
>> rafaelrodrigues.machado@gmail.com> wrote:
>>> 
>>> Hi everyone
>>> 
>>> I have a question.
>>> Let's suppose I have a BIOS with several FV regions. Between these FV
>> there
>>> is one that is empty.
>>> 
>>> My question is:
>>> In case I get this BIOS and inject a dxe driver at this FV. Would it be
>>> executed, or there are specific FVs that are considered as containers to
>>> executable code avoiding other FVs content to be executed?
>>> 
>>> In case the answer comes with some code examples from edk2 tree it would
>> be
>>> amazing :)
>>> 
>>> Thanks and Regards
>>> Rafael
>>> _______________________________________________
>>> edk2-devel mailing list
>>> edk2-devel@lists.01.org
>>> https://lists.01.org/mailman/listinfo/edk2-devel
>> 
>> 
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