[Bug 1065261] [NEW] efibootmgr -w overwrites existing unique MBR signature

[Colin Watson]

Public bug reported:

Kano reported on IRC that efibootmgr -w overwrites an existing unique
MBR signature, and that this can break existing Windows installations.
I had assumed that -w was "write unique MBR signature if that field is
zero", but code inspection confirms that it's "write unique MBR
signature no matter what".

However, I don't want to just drop -w; I'd much rather have the best of
both worlds and leave existing signatures in place but also write a new
signature if it's zero.  My reading of the UEFI spec strongly encourages
writing a signature; it notes for example that this field is always set
by the OS, never by the firmware.

** Affects: grub2 (Ubuntu)
     Importance: Critical
     Assignee: Colin Watson (cjwatson)
         Status: Triaged

** Affects: grub2 (Ubuntu Quantal)
     Importance: Critical
     Assignee: Colin Watson (cjwatson)
         Status: Triaged

** Also affects: grub2 (Ubuntu Quantal)
   Importance: Undecided
       Status: New

** Changed in: grub2 (Ubuntu Quantal)
       Status: New => Triaged

** Changed in: grub2 (Ubuntu Quantal)
   Importance: Undecided => Critical

** Changed in: grub2 (Ubuntu Quantal)
     Assignee: (unassigned) => Colin Watson (cjwatson)

** Changed in: grub2 (Ubuntu Quantal)
    Milestone: None => ubuntu-12.10

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https://bugs.launchpad.net/bugs/1065261

Title:
  efibootmgr -w overwrites existing unique MBR signature

Status in “grub2” package in Ubuntu:
  Triaged
Status in “grub2” source package in Quantal:
  Triaged

Bug description:
  Kano reported on IRC that efibootmgr -w overwrites an existing unique
  MBR signature, and that this can break existing Windows installations.
  I had assumed that -w was "write unique MBR signature if that field is
  zero", but code inspection confirms that it's "write unique MBR
  signature no matter what".

  However, I don't want to just drop -w; I'd much rather have the best
  of both worlds and leave existing signatures in place but also write a
  new signature if it's zero.  My reading of the UEFI spec strongly
  encourages writing a signature; it notes for example that this field
  is always set by the OS, never by the firmware.

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