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

[dann frazier]

Public bug reported:

[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/pull/107

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

** Affects: grub2 (Ubuntu)
     Importance: Undecided
         Status: New

** Affects: grub2 (Ubuntu Bionic)
     Importance: Undecided
         Status: New

** Affects: grub2 (Ubuntu Focal)
     Importance: Undecided
         Status: New

** Affects: grub2 (Ubuntu Jammy)
     Importance: Undecided
         Status: New

** Affects: grub2 (Ubuntu Kinetic)
     Importance: Undecided
         Status: New

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

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

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

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

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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 package in Ubuntu:
  New
Status in grub2 source package in Bionic:
  New
Status in grub2 source package in Focal:
  New
Status in grub2 source package in Jammy:
  New
Status in grub2 source package in Kinetic:
  New

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/pull/107

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

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