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

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <24245.1516205816@warthog.procyon.org.uk>
Date:   Wed, 17 Jan 2018 16:16:56 +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

Jiri Bohac <jbohac@...e.cz> wrote:

> > 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.
> 
> yes, to be clear, the problem I'm trying to fix is:
> - without CONFIG_KEXEC_VERIFY_SIG kexec in a locked down kernel
>   will not work at all -> every distro that wants to support
>   secureboot will need to enable CONFIG_KEXEC_VERIFY_SIG;
> 
> - once CONFIG_KEXEC_VERIFY_SIG is enabled, kexec images need to
>   be signed even if secureboot is not used
>
> The problem is that CONFIG_KEXEC_VERIFY_SIG enables both the
> implementation and the enforcement of the signature checking.

Yep.  I understand that.

> What I'm proposing are new config options that allow a kernel to
> be compiled in such a way that:
> - kexec works even without signatures if secureboot is off
> - kexec works with secureboot but requires signed images

Agreed to both of those.  I also agree with making it possible to
configurationally require signatures, which your first patch does.

> The semantics should be the same as with signed modules, because
> requiring kexec signatures when you can load unsigned modules is
> futile. But with your original patchset, that's exactly what
> distro kernels will be doing when booted with secureboot off,
> MODULE_SIG_FORCE=n and KEXEC_VERIFY_SIG=y.

I should fix that.

David