* Steven Rostedt: > Once locked down is set, can it ever be undone without rebooting? I think this is the original intent with such patches, yes. But then reality interferes and people add some escape hatch, so that it's possible again to load arbitrary kernel modules. And for servers, you can't have a meaningful physical presence check, so you end up with a lot of complexity for something that offers absolutely zero gains in security. The other practical issue is that general-purpose Linux distributions cannot prevent kernel downgrades, so even if there's a cryptographically signed chain from the firmware to the kernel, you can boot last year's kernel, use a root-to-ring-0 exploit to disable its particular implementation of lockdown, and then kexec the real kernel with lockdown disabled. I'm sure that kernel lockdown has applications somewhere, but for general-purpose distributions (who usually want to support third-party kernel modules), it's an endless source of problems that wouldn't exist without it.
