linux-kernel - Re: [PATCH v3] KEYS: trusted: Fix trusted key backends when building as module

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Date:   Mon, 27 Sep 2021 16:33:08 -0400
From:   Mimi Zohar <zohar@...ux.ibm.com>
To:     Andreas Rammhold <andreas@...mhold.de>
Cc:     Ahmad Fatoum <a.fatoum@...gutronix.de>,
        James Bottomley <jejb@...ux.ibm.com>,
        Jarkko Sakkinen <jarkko@...nel.org>,
        David Howells <dhowells@...hat.com>,
        James Morris <jmorris@...ei.org>,
        "Serge E. Hallyn" <serge@...lyn.com>,
        Sumit Garg <sumit.garg@...aro.org>,
        linux-integrity@...r.kernel.org, keyrings@...r.kernel.org,
        linux-security-module@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3] KEYS: trusted: Fix trusted key backends when
 building as module

On Mon, 2021-09-27 at 22:08 +0200, Andreas Rammhold wrote:
> On 07:27 27.09.21, Mimi Zohar wrote:
> > On Mon, 2021-09-27 at 10:51 +0200, Andreas Rammhold wrote:
> > > On 09:47 13.09.21, Ahmad Fatoum wrote:
> > > > Dear trusted key maintainers,
> > > > 
> > > > On 30.07.21 03:28, Andreas Rammhold wrote:
> > > > > Before this commit the kernel could end up with no trusted key sources
> > > > > even though both of the currently supported backends (TPM and TEE) were
> > > > > compiled as modules. This manifested in the trusted key type not being
> > > > > registered at all.
> > > > > 
> > > > > When checking if a CONFIG_… preprocessor variable is defined we only
> > > > > test for the builtin (=y) case and not the module (=m) case. By using
> > > > > the IS_REACHABLE() macro we do test for both cases.
> > > > > 
> > > > > Fixes: 5d0682be3189 ("KEYS: trusted: Add generic trusted keys framework")
> > > > > Signed-off-by: Andreas Rammhold <andreas@...mhold.de>
> > > > > Reviewed-by: Jarkko Sakkinen <jarkko@...nel.org>
> > > > Does anyone intend to pick this up?
> > > 
> > > Did this end up in any tree by now? I am wondering if I should resend
> > > the patch instead. Perhaps it was just overlooked?
> > 
> > For EVM environments only using trusted and encrypted keys, not file
> > signatures, the trusted key is needed to decrypt the "master" key in
> > order to verify kernel modules.
> 
> So what you are saying is that right now (before this patch & after this
> patch) you could compile a kernel that wouldn't be able to load any
> modules when the trusted keychain part is built as module?

Before this patch, trusted and encrypted keys are builtin, so verifying
kernel modules with security.evm containing an EVM hmac would succeed. 
Afterwards it would fail, as there's a dependency on the trusted key to
verify the integrity of the trusted key module.

Mimi