Built in grub gpg verification fails over tftp

Issue

• While booting an x86_64 efi image over tftp on a vmware 10 instance fails.
• The issue can be seen in rhel7 grub 2.02 when using a gpg public key with check_sigantures enabled.
• All file operations over tftp complete, but grub immediately throws the following error:

alloc magic is broken at <addr>: <value>
Aborted. Press any key to exit.

• Pressing a key takes us back to the EFI firmware.
• We can work around the issue by disabling check signatures and manually running verify_detached on a file.
• However, we have to pull the kernel and initrd twice, which doubles the boot time.
• Signature checking from a memdisk does not appear to be broken.