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 12:59:15 +0100
From:   Jiri Bohac <jbohac@...e.cz>
To:     David Howells <dhowells@...hat.com>
Cc:     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

Hi,

sorry for replying to such an old thread.

On Thu, Nov 09, 2017 at 05:31:38PM +0000, David Howells wrote:
> When KEXEC_VERIFY_SIG is not enabled, kernel should not load images through
> kexec_file systemcall if the kernel is locked down unless IMA can be used
> to validate the image.

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.

Distribution kernels will then have KEXEC_VERIFY_SIG on and
everyone will need signed kexec images even when totally
uninterested in secureboot.

So instead of this patch, I propose the two followup patches that
split KEXEC_VERIFY_SIG into KEXEC_SIG and KEXEC_SIG_FORCE just as
we have with modules:

[PATCH 08a/30] kexec_file: split KEXEC_VERIFY_SIG into KEXEC_SIG and KEXEC_SIG_FORCE
[PATCH 08b/30] kexec_file: Restrict at runtime if the kernel is locked down

Lockdown would not require KEXEC_SIG_FORCE but when enabled it
would check the signature.

Thanks,

-- 
Jiri Bohac <jbohac@...e.cz>
SUSE Labs, Prague, Czechia