linux-kernel - Re: [PATCH 08/30] kexec_file: Restrict at runtime if the kernel is locked down

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Date:   Thu, 11 Jan 2018 12:47:57 +0000
From:   David Howells <dhowells@...hat.com>
To:     Jiri Bohac <jbohac@...e.cz>
Cc:     dhowells@...hat.com, linux-security-module@...r.kernel.org,
        gnomes@...rguk.ukuu.org.uk, linux-efi@...r.kernel.org,
        linux-kernel@...r.kernel.org, jforbes@...hat.com,
        Chun-Yi Lee <joeyli.kernel@...il.com>
Subject: Re: [PATCH 08/30] kexec_file: Restrict at runtime if the kernel is locked down

David Howells <dhowells@...hat.com> wrote:

> > I don't like the idea that the lockdown (which is a runtime
> > thing) requires a compile time option (KEXEC_VERIFY_SIG) that
> > forces the verification even when the kernel is then not locked
> > down at runtime.
> 
> It doesn't.  The EPERM only triggers if:
> 
>  (1) File signatures aren't mandatory (ie. CONFIG_KEXEC_VERIFY_SIG) is not
>      set, and
> 
>  (2) you're not using IMA appraisal to validate the file contents, and
> 
>  (3) lockdown mode is enabled.
> 
> If file signatures are mandatory or IMA appraisal is in use, then the lockdown
> state doesn't need to be checked.

Having said that, I do see your point, I think.  We should still let through
validly signed images, even if signatures aren't mandatory in lockdown mode.

David