Re: [PATCH V34 09/29] kexec_file: Restrict at runtime if the kernel is locked down

Matthew Garrett
2019-06-27T15:28:23Z

On Wed, Jun 26, 2019 at 9:59 PM James Morris <jmorris@namei.org> wrote:
> This is not a criticism of the patch but a related issue which I haven't
> seen discussed (apologies if it has).
>
> If signed code is loaded into ring 0, verified by the kernel, then
> executed, you still lose your secure/trusted/verified boot state. If the
> currently running kernel has been runtime-compromised, any signature
> verification performed by the kernel cannot be trusted.
>
> This problem is out of scope for the lockdown threat model (which
> naturally cannot include a compromised kernel), but folk should be aware
> that signature-verified kexec does not provide equivalent assurance to a
> full reboot on a secure-boot system.

By that metric, on a secure boot system how do we determine that code
running in the firmware environment wasn't compromised before it
launched the initial signed kernel?