Re: [PATCH 1/2] efi/x86: Move efi stub globals from .bss to .data

Ard Biesheuvel
2020-04-08T07:49:15Z

(add Peter, Leif and Daniel)

On Wed, 8 Apr 2020 at 09:43, Dave Young <dyoung-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org> wrote:
>
> On 04/06/20 at 02:06pm, Arvind Sankar wrote:
> > Commit
> >
> > 3ee372ccce4d ("x86/boot/compressed/64: Remove .bss/.pgtable from
> > bzImage")
> >
> > removed the .bss section from the bzImage.
> >
> > However, while a PE loader is required to zero-initialize the .bss
> > section before calling the PE entry point, the EFI handover protocol
> > does not currently document any requirement that .bss be initialized by
> > the bootloader prior to calling the handover entry.
> >
> > When systemd-boot is used to boot a unified kernel image [1], the image
> > is constructed by embedding the bzImage as a .linux section in a PE
> > executable that contains a small stub loader from systemd together with
> > additional sections and potentially an initrd. As the .bss section
> > within the bzImage is no longer explicitly present as part of the file,
> > it is not initialized before calling the EFI handover entry.
> > Furthermore, as the size of the embedded .linux section is only the size
> > of the bzImage file itself, the .bss section's memory may not even have
> > been allocated.
>
> I did not follow up the old report, maybe I missed something. But not
> sure why only systemd-boot is mentioned here. I also have similar issue
> with early efi failure. With these two patches applied, it works well
> then.
>
> BTW, I use Fedora 31 + Grub2
>

OK, so I take it this means that GRUB's PE/COFF loader does not
zero-initialize BSS either? Does it honor the image size in memory if
it exceeds the file size?