[PATCH 1/2] efi: Add dependency on M-mode for RISC-V

[Sean Anderson]

On 9/28/20 12:27 PM, Heinrich Schuchardt wrote:
> On 28.09.20 18:08, Sean Anderson wrote:
>> >From section 2.3.7 of the UEFI specification:
>>
>>> RISC-V UEFI will only be executed in machine mode. The machine mode has
>>> the highest privilege and this mode is the only mandatory privilege level
>>> for RISC-V platforms; all other privilege levels are optional depending
>>> on the platform requirements. Machine mode is the first mode entered at
>>> the power-on reset. This level is used in UEFI for low-level access to a
>>> hardware platform.
>>
>> Signed-off-by: Sean Anderson <seanga2 at gmail.com>
>> ---
>>
>>  lib/efi_loader/Kconfig | 2 ++
>>  1 file changed, 2 insertions(+)
>>
>> diff --git a/lib/efi_loader/Kconfig b/lib/efi_loader/Kconfig
>> index bad1a29ba8..2197c84bf3 100644
>> --- a/lib/efi_loader/Kconfig
>> +++ b/lib/efi_loader/Kconfig
>> @@ -10,6 +10,8 @@ config EFI_LOADER
>>  	depends on !EFI_STUB || !X86_64 || EFI_STUB_64BIT
>>  	# We need EFI_STUB_32BIT to be set on x86_32 with EFI_STUB
>>  	depends on !EFI_STUB || !X86 || X86_64 || EFI_STUB_32BIT
>> +	# RISC-V UEFI must run in machine mode
>> +	depends on !RISCV || RISCV_M_MODE
>>  	default y if !ARM || SYS_CPU = armv7 || SYS_CPU = armv8
>>  	select LIB_UUID
>>  	select HAVE_BLOCK_DEVICE
>>
> 
> Hello Sean,
> 
> the specification is wrong. A change request has been made to correct
> the specification. We should not change U-Boot here.
> 
> See the discussion in this thread:
> https://lists.linaro.org/pipermail/boot-architecture/2020-September/001481.html
> 
> Best regards
> 
> Heinrich
> 

Thanks for linking that. I'm glad some of these issues are being addressed. However, I am concerned about your suggestion

> * Don't trust the values of tp and gp when entered
>   from the payloads world.

Because tp *must* be trusted in S-Mode...

Of course, all this could be averted by adding an sbi_get_mhartid function...

--Sean