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

[dann frazier]

= verification =
I've rebooted a BlueField 2 device several times with this update. I've neither seen a hang nor any sign of regression.

ubuntu at localhost:~$ dpkg -l | grep grub
ii  grub-common                        2.04-1ubuntu26.16                                        arm64        GRand Unified Bootloader (common files)
ii  grub-efi-arm64                     2.04-1ubuntu47.5                                         arm64        GRand Unified Bootloader, version 2 (ARM64 UEFI version)
ii  grub-efi-arm64-bin                 2.04-1ubuntu47.5                                         arm64        GRand Unified Bootloader, version 2 (ARM64 UEFI modules)
ii  grub-efi-arm64-signed              1.173.4+2.04-1ubuntu47.5                                 arm64        GRand Unified Bootloader, version 2 (EFI-ARM64 version, signed)
ii  grub2-common                       2.04-1ubuntu26.16                                        arm64        GRand Unified Bootloader (common files for version 2)


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