[Bug 1987924] Re: GRUB may execute the kernel w/ dirty instruction cache on arm64

[Steve Langasek]

Hello dann, or anyone else affected,

Accepted grub2-unsigned into focal-proposed. The package will build now
and be available at
https://launchpad.net/ubuntu/+source/grub2-unsigned/2.04-1ubuntu47.5 in
a few hours, and then in the -proposed repository.

Please help us by testing this new package.  See
https://wiki.ubuntu.com/Testing/EnableProposed for documentation on how
to enable and use -proposed.  Your feedback will aid us getting this
update out to other Ubuntu users.

If this package fixes the bug for you, please add a comment to this bug,
mentioning the version of the package you tested, what testing has been
performed on the package and change the tag from verification-needed-
focal to verification-done-focal. If it does not fix the bug for you,
please add a comment stating that, and change the tag to verification-
failed-focal. In either case, without details of your testing we will
not be able to proceed.

Further information regarding the verification process can be found at
https://wiki.ubuntu.com/QATeam/PerformingSRUVerification .  Thank you in
advance for helping!

N.B. The updated package will be released to -updates after the bug(s)
fixed by this package have been verified and the package has been in
-proposed for a minimum of 7 days.

** Changed in: grub2-unsigned (Ubuntu Focal)
       Status: New => Fix Committed

** Tags added: verification-needed verification-needed-focal

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https://bugs.launchpad.net/bugs/1987924

Title:
  GRUB may execute the kernel w/ dirty instruction cache on arm64

Status in grub2-unsigned package in Ubuntu:
  Fix Released
Status in grub2-unsigned source package in Bionic:
  New
Status in grub2-unsigned source package in Focal:
  Fix Committed
Status in grub2-unsigned source package in Jammy:
  New
Status in grub2-unsigned source package in Kinetic:
  Fix Released

Bug description:
  [Impact]
  Similar to bug 1987541, where shim may execute GRUB w/ polluted instruction cache, GRUB itself also fails to flush the instruction cache for the kernel memory before starting it. This is believed to be the source of some rare crashes seen executing instructions in the kernel EFI stub.

  [Test Case]
  Put an arm64 server in a reboot loop and watch for a crash (synchronous exception abort) after GRUB has started executing the kernel.

  [Fix]
  https://github.com/rhboot/grub2/commit/4e9020a937a30873fa63ba34e16c1e6fb7e7b718

  [What could go wrong]
  The only risk I can identify is possibly-measurable performance impact to booting the kernel.

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