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grub mishandles corrupt/missing primary GPT


From: Chris Murphy
Subject: grub mishandles corrupt/missing primary GPT
Date: Wed, 23 Oct 2013 19:38:52 -0600

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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