linux-kernel - Re: [PATCH v2] builddeb: Support signing kernels with the module signing key

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Date:   Thu, 10 Feb 2022 08:03:44 +0900
From:   Masahiro Yamada <masahiroy@...nel.org>
To:     Julian Andres Klode <julian.klode@...onical.com>
Cc:     Matthew Wilcox <willy@...radead.org>,
        Ben Hutchings <ben@...adent.org.uk>,
        linux-efi <linux-efi@...r.kernel.org>,
        Linux Kbuild mailing list <linux-kbuild@...r.kernel.org>,
        efi@...ts.einval.com,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        David Howells <dhowells@...hat.com>, keyrings@...r.kernel.org,
        David Woodhouse <dwmw2@...radead.org>,
        debian-kernel <debian-kernel@...ts.debian.org>
Subject: Re: [PATCH v2] builddeb: Support signing kernels with the module
 signing key

On Wed, Feb 9, 2022 at 1:13 AM Julian Andres Klode
<julian.klode@...onical.com> wrote:
>
> On Tue, Feb 08, 2022 at 01:10:34PM +0000, Matthew Wilcox wrote:
> > On Tue, Feb 08, 2022 at 12:01:22PM +0100, Julian Andres Klode wrote:
> > > It's worth pointing out that in Ubuntu, the generated MOK key
> > > is for module signing only (extended key usage 1.3.6.1.4.1.2312.16.1.2),
> > > kernels signed with it will NOT be bootable.
> >
> > Why should these be separate keys?  There's no meaningful security
> > boundary between a kernel module and the ernel itself; a kernel
> > modulecan, for example, write to CR3, and that's game over for
> > any pretence at separation.
>
> I don't really _know_, but I believe the difference is that the
> kernel binaries runs in boot services, and calls ExitBootServices,
> whereas modules are loaded after ExitBootServices.
>
> But I don't know the full rationale why (a) the feature exists in
> the first place and (b) why the Ubuntu security team chose to require
> that constraint.
>
> My goal is just to make people aware of that so they can make
> informed decisions :)
>
> --
> debian developer - deb.li/jak | jak-linux.org - free software dev
> ubuntu core developer                              i speak de, en


So, this is the restriction only for Ubuntu.

If it works for Debian, I am fine with
adding the kernel signing to scripts/package/builddeb.

If it is annoying for some people, maybe we can add
some switch like KDEB_SIGN_KERNEL to conditionally
sign the kernel.

-- 
Best Regards
Masahiro Yamada