[PATCH] efi: Restrict the simple file system protocol to support only FAT

[Ilias Apalodimas]

On Thu, Jun 03, 2021 at 03:36:38PM +0900, Masami Hiramatsu wrote:
> Hi Ilias,
> 
> 2021年6月3日(木) 15:25 Ilias Apalodimas <ilias.apalodimas at linaro.org>:
> >
> > [...]
> > > >
> > > > At least Debian and Ubuntu do not allow /boot to be on a FAT file system. If we want to boot Linux via the EFI stub without GRUB, we need ext4 support exposed to the EFI sub-system. See Ilias' recent contributions for the EFI_LOAD_FILE2_PROTOCOL for initrd and efidebug. This came in handy for booting via EFI on RISC-V where the initrd= command line parameter is not supported by Linux.
> > >
> > > IMHO, such dependency is out of UEFI spec. That means Debian/Ubuntu
> > > doesn't follow the UEFI spec. (but as far as I know, those install ESP
> > > on the disk and install GRUB efi application for boot)
> > > And yes, EFI_LOAD_FILE2_PROTOCOL needs to load initrd from somewhere
> > > (I'm usually put it on the ESP). But, if the EFI_LOAD_FILE2_PROTOCOL
> > > *requires* to access ext4 partition, I think that is not supported by
> > > UEFI spec.
> >
> > One of the advantages in using EFI_LOAD_FILE2_PROTOCOL is that you can load
> > it from *any* file system the firmware has access to. The only thing the
> > kernel does is provide a buffer big enough to fit in the initrd.  The
> > firmware is free to locate the file and copy it in that memory however it
> > sees fit.
> 
> Ah, I got it. Yes, EFI_LOAD_FILE2_PROTOCOL doesn't depend on the
> EFI_SIMPLE_FILE_SYSTEM_PROTOCOL. Thus it should be able to load
> the file from where the U-Boot can access. However, since current implementation
> depends on the EFI_SIMPLE_FILE_SYSTEM_PROTOCOL, my patch limits
> the ability...
> 

Yea that changed recently. On the first version, I was using u-boot
internal functions to locate and load the file.  When we decided to store a
device path on Boot#### options, in order to locate the initrd, we started
using the EFI APIs to load it. You can check commit 53f6a5aa8626 for more
details.

Cheers
/Ilias
> Thank you,
> 
> >
> > Cheers
> > /Ilias
> > >
> > > Anyway, I agree that denying access to non-FAT partitions is too
> > > restricted. What about my other ideas? If the volume is set to
> > > ReadOnly, that is good for both of the SCT and the
> > > EFI_LOAD_FILE2_PROTOCOL.
> > >
> > >
> > > Thank you,
> > >
> > > >
> > > > Best regards
> > > >
> > > > Heinrich
> > > >
> > > >
> 
> 
> 
> -- 
> Masami Hiramatsu