Useful Buildroot Defconfigs not included in the normal release
x86_64-efi
After building, convert the disk image to a vdi with: VBoxManage convertfromraw output/images/disk.img output/images/disk.vdi
If you have rebuilt the disk image, it won't match the UUID kept in your Virtualbox database, so get it from the error box and update it with: VBoxManage internalcommands sethduuid "/full/path/to/buildroot/output/images/disk.vdi" [UUID]