linux-kernel - Re: sign-file and detached PKCS#7 firmware signatures

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Message-ID: <CAB=NE6UT57VDg9OBYPVOq-xtZDqw-9UM79_sSP7jGb2Ev2NUeA@mail.gmail.com>
Date:	Tue, 19 May 2015 13:12:38 -0700
From:	"Luis R. Rodriguez" <mcgrof@...e.com>
To:	David Howells <dhowells@...hat.com>
Cc:	Rusty Russell <rusty@...tcorp.com.au>,
	Michal Marek <mmarek@...e.cz>,
	Matthew Garrett <mjg59@...f.ucam.org>, keyrings@...ux-nfs.org,
	dmitry.kasatkin@...il.com,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Seth Forshee <seth.forshee@...onical.com>,
	linux-security-module <linux-security-module@...r.kernel.org>,
	David Woodhouse <dwmw2@...radead.org>
Subject: Re: sign-file and detached PKCS#7 firmware signatures

On Tue, May 19, 2015 at 11:47 AM, David Howells <dhowells@...hat.com> wrote:
> Luis R. Rodriguez <mcgrof@...e.com> wrote:
>
>> I'll also mention:
>>
>> ---
>> The $DIGEST_ALGORITHM needs to be supported on the running kernel and
>> can differ from CONFIG_MODULE_SIG_HASH.
>> ---
>>
>> As I do no think that is quite obvious to a system integrator at first.
>
> Actually, this isn't necessarily so for the firmware.

Sorry by "needs to be supported on the running kernel" I meant "=y" or "=m".

> It *is* for the module signing, but you can always load the module to give you
> the digest algorithm (or public key algorithm) for the firmware.

Sure.

> Though you would still have to be careful with firmware loaded during the
> initramfs phase.

Make sense, how about:

---
The $DIGEST_ALGORITHM needs to be enabled as built-in (=y) or modular
(=m) in the running kernel and can differ from CONFIG_MODULE_SIG_HASH.
If you are enabling the $DIGEST_ALGORITHM as a module take care to
ensure that this module will also be present on the initramfs used as
some modules within the initramfs may need it if using the
firmware_class APIs and firmware signing has been enabled.
---

  Luis
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