GNU GRUB 2.14: serial-MMIO lockdown bypass in Canonical-signed gcdx64.efi

<p>Posted by Luppa on Sep 13</p>== Overview ==<br /> <br /> Canonical-signed GRUB2 (grub-efi-amd64-signed), when admitted by UEFI<br /> Secure Boot and reporting lockdown=y, exposes a serial command that accepts<br /> a caller-supplied 64-bit MMIO base address. The lockdown path does not<br /> restrict this command, and the serial implementation does not validate that<br /> the requested register