Dev-mode only boots official kernels by default
Although we're now using a single unified BIOS, it is pretty nice to be able
to get a shell in developer mode while still using verified boot for the
kernel and filesystem. Alex & ZGB implemented this by requiring the dev-mode
user to install a special dev-mode BIOS. We don't do that, but we DO require
setting a special flag with "crossystem" to accomplish the same thing.
In order to allow booting a self-signed kernel, you must boot in developer
mode, open a shell, and run this:
Special note to internal developers: If you're in the habit (as I am) of
booting directly from a USB stick in dev-mode, you'll have to run this:
crossystem dev_boot_custom=1 dev_boot_usb=1
Just using dev_boot_usb=1 is no longer enough, because the USB kernel is
signed using the recovery key and by pressing Ctrl-U, we validate it with
the kernel data key. That worked before this change because any self-signed
kernel was fine, and that's how the USB key was treated. Now it actually
requires a verified signature until you enable dev_boot_custom=1 also.
Boot once in normal mode, which clears the special flags. Then switch to
developer mode. You should be able to boot and get a root shell.
Obtain a USB recovery image that's keyed differently. For example, if you're
testing with dev-keys, use a PVT-signed image or vice-versa.
Reboot into dev-mode with the USB recovery stick inserted. At the dev-mode
screen, press Ctrl-U. You should hear a single beep, but it should not boot.
Press Ctrl-D to boot from the hard drive, log in to a shell and run
Repeat the previous test. This time when you press Ctrl-U, it should boot
the recovery image. Turn the system off before it does anything.
Tested-by: Bill Richardson <firstname.lastname@example.org>
Reviewed-by: Randall Spangler <email@example.com>
9 files changed