linux-kernel - Re: [PATCH v6 00/13] Enroll kernel keys thru MOK

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Date:   Thu, 16 Sep 2021 16:03:33 -0400
From:   Nayna <nayna@...ux.vnet.ibm.com>
To:     Eric Snowberg <eric.snowberg@...cle.com>, keyrings@...r.kernel.org,
        linux-integrity@...r.kernel.org, zohar@...ux.ibm.com,
        dhowells@...hat.com, dwmw2@...radead.org,
        herbert@...dor.apana.org.au, davem@...emloft.net,
        jarkko@...nel.org, jmorris@...ei.org, serge@...lyn.com
Cc:     keescook@...omium.org, gregkh@...uxfoundation.org,
        torvalds@...ux-foundation.org, scott.branden@...adcom.com,
        weiyongjun1@...wei.com, nayna@...ux.ibm.com, ebiggers@...gle.com,
        ardb@...nel.org, nramas@...ux.microsoft.com, lszubowi@...hat.com,
        linux-kernel@...r.kernel.org, linux-crypto@...r.kernel.org,
        linux-security-module@...r.kernel.org,
        James.Bottomley@...senPartnership.com, pjones@...hat.com,
        konrad.wilk@...cle.com
Subject: Re: [PATCH v6 00/13] Enroll kernel keys thru MOK


On 9/14/21 5:14 PM, Eric Snowberg wrote:
> Back in 2013 Linus requested a feature to allow end-users to have the
> ability "to add their own keys and sign modules they trust". This was
> his *second* order outlined here [1]. There have been many attempts
> over the years to solve this problem, all have been rejected.  Many
> of the failed attempts loaded all preboot firmware keys into the kernel,
> including the Secure Boot keys. Many distributions carry one of these
> rejected attempts [2], [3], [4]. This series tries to solve this problem
> with a solution that takes into account all the problems brought up in
> the previous attempts.
>
> On UEFI based systems, this series introduces a new Linux kernel keyring
> containing the Machine Owner Keys (MOK) called machine. It also defines
> a new MOK variable in shim. This variable allows the end-user to decide
> if they want to load MOK keys into the machine keyring. Mimi has suggested
> that only CA keys contained within the MOK be loaded into the machine
> keyring. All other certs will load into the platform keyring instead.
>
> By default, nothing changes; MOK keys are not loaded into the machine
> keyring.  They are only loaded after the end-user makes the decision
> themselves.  The end-user would set this through mokutil using a new
> --trust-mok option [5]. This would work similar to how the kernel uses
> MOK variables to enable/disable signature validation as well as use/ignore
> the db. Any kernel operation that uses either the builtin or secondary
> trusted keys as a trust source shall also reference the new machine
> keyring as a trust source.
>
> Secure Boot keys will never be loaded into the machine keyring.  They
> will always be loaded into the platform keyring.  If an end-user wanted
> to load one, they would need to enroll it into the MOK.
>
> Steps required by the end user:
>
> Sign kernel module with user created key:
> $ /usr/src/kernels/$(uname -r)/scripts/sign-file sha512 \
>     machine_signing_key.priv machine_signing_key.x509 my_module.ko
>
> Import the key into the MOK
> $ mokutil --import machine_signing_key.x509
>
> Setup the kernel to load MOK keys into the .machine keyring
> $ mokutil --trust-mok
>
> Then reboot, the MokManager will load and ask if you want to trust the
> MOK key and enroll the MOK into the MOKList.  Afterwards the signed kernel
> module will load.

machine_signing_key.x509 appears to be a code-signing, self-signed key.  
It's not a CA key, but the intent of the patchset is to load only CA 
keys to .machine keyring.

Shouldn't there be two steps: one to load the CA key into MOK, and a 
second one to load the code-signing key which is signed by this CA ?

Thanks & Regards,

       - Nayna