Why does the firmware memory region have no permissions?

[Daniel Schaefer]

Whoops, put CC as subject...

On 5/12/21 6:20 PM, Daniel Schaefer wrote:
> Hi Anup,
> 
> I'm in the process of upgrading EDKII to OpenSBI 0.9 and using the Generic Platform.
> 
> Previously we were doing sbi_init with M-Mode, adding our SBI extension and
> then calling sbi_switch_mode to switch to S-Mode. Now sbi_init disallows
> initializing to M-Mode, so I'm directly switching to S-Mode. It seems that even
> from S-Mode I can register our SBI extension with sbi_ecall_register_extension.
> Is that correct?
> 
> However, sbi_init when directly initializing to S-Mode checks that the start_address is executable.
> So I'm wondering why the FW region isn't set as executable in OpenSBI?
> How do other FWs like U-Boot get around this?
> 
> https://github.com/riscv/opensbi/commit/b1678af210dc4b4e6d586d6d96617e9641618994#diff-6e8e352a8a90ba5a7adbb58a806ed9b6404c2c67db416332f9c05a6b322eecd6R346
> 
> If I try to set my own regions by adding .domains_root_regions I get another
> error because OpenSBI checks that I have a region that is the same as the FW
> region added by OpenSBI. If I duplicate the FW region and mark the first one as
> executable I can pass the executable check and also the check that there's an
> FW region.
> Additionally we have to manually call pmp_set in our custom platform to make
> the FW region RWX.
> 
> That seems like a workaround, however. Do you have any suggestion to properly fix it?
> I'm sure we're misunderstand something.
> 
> For context: We're writing the start addr and size of our FW image into the
> scratch space before OpenSBI is initialized. Therefore we're expecting it to
> set the PMP settings correctly.
> 
> Please check out my workaround commit: https://github.com/riscv/riscv-edk2-platforms/commit/a5ac63096ca5da795042baf650170643fe219cab
> 
> Thanks,
> Daniel
>