Re: [GIT PULL] Kernel lockdown for secure boot

From: Matthew Garrett
Date: Wed Apr 04 2018 - 12:22:26 EST

On Wed, Apr 4, 2018 at 6:52 AM Theodore Y. Ts'o <tytso@xxxxxxx> wrote:

> On Wed, Apr 04, 2018 at 02:33:37PM +0100, David Howells wrote:
> > Theodore Y. Ts'o <tytso@xxxxxxx> wrote:
> >
> > > Whoa. Why doesn't lockdown prevent kexec? Put another away, why
> > > isn't this a problem for people who are fearful that Linux could be
> > > used as part of a Windows boot virus in a Secure UEFI context?
> >
> > Lockdown mode restricts kexec to booting an authorised image (where the
> > authorisation may be by signature or by IMA).

> If that's true, then Matthew's assertion that lockdown w/o secure boot
> is insecure goes away, no?

If you don't have secure boot then an attacker with root can modify your
bootloader or kernel, and on next boot lockdown can be silently disabled.