Improve GRUB_SIGN_VERIFY protections #98
Description
We can reach the same level of protection provided by shim + SELoader but only using PGP signing by levering few spots:
- Fix the -s test flag that should add GRUB_FILE_TYPE_SKIP_SIGNATURE flags in order to test the presence of the file ignoring the the signature file in this case (even if doesn't seems to be a good idea to use it -s flaw in grub-efi.cfg? #97)
- Force the verifier to set the grub_errno if it fails to verify (https://github.com/rhboot/grub2/blob/fedora-39/grub-core/kern/verifiers.c#L204)
- Don't let pass the grub_file_open on GRUB_ERR_BAD_SIGNATURE (https://github.com/rhboot/grub2/blob/fedora-39/grub-core/kern/file.c#L150): Error message, sleep, reboot . Which cover all file openings globally, like buffiles, initrd, kernel. Every file opened by the grub2 has to be correctly signed (if no GRUB_FILE_TYPE_SKIP_SIGNATURE is set)
- Don't ignore error on source commands (https://github.com/rhboot/grub2/blob/fedora-39/grub-core/normal/main.c#L287): Removing the signature of the sourced file will make the source to fail and may completly change the behaviour of the wanted process (even with a fix for -s flaw in grub-efi.cfg? #97, the source will not be executed). Which is handled by this patch in the case of mok2verify:
(I have patch for this issue, but for kirkstone branch. I may try to port it)