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

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Message-ID: <YgJrypdQium7AcWV@casper.infradead.org>
Date:   Tue, 8 Feb 2022 13:10:34 +0000
From:   Matthew Wilcox <willy@...radead.org>
To:     Julian Andres Klode <julian.klode@...onical.com>
Cc:     Masahiro Yamada <masahiroy@...nel.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 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.