https://bugzilla.redhat.com/show_bug.cgi?id=1022743
Gist is, starting with a disk with valid PMBR, primary GPT, and backup GPT, if
I zero LBA 2, I can no longer boot from the disk. I get a grub rescue prompt.
Instead, if I merely corrupt a portion of the first partitiontypeguid to mimic
corruption, I can still boot, whereas this primary GPT fails checksums with
both gdisk and parted.
This tells me that GRUB isn't checking for the validity of the primary GPT. And
GRUB doesn't ever use the backup GPT.
Expected behavior is GRUB should check if the MBR is a PMBR (1st and only entry
is type 0xEE) and if not then consider the disk MBR. If it is PMBR, check
validity of the primary GPT header+table, if valid use it. If invalid, check
validity of backup GPT header+table, if valid use it. If invalid, fail.
Chris Murphy
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