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

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Date:   Wed, 15 Sep 2021 15:28:39 -0600
From:   Eric Snowberg <eric.snowberg@...cle.com>
To:     Jarkko Sakkinen <jarkko@...nel.org>
Cc:     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,
        jmorris@...ei.org, serge@...lyn.com, 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" <konrad.wilk@...cle.com>
Subject: Re: [PATCH v6 00/13] Enroll kernel keys thru MOK


> On Sep 15, 2021, at 11:57 AM, Jarkko Sakkinen <jarkko@...nel.org> wrote:
> 
> On Tue, 2021-09-14 at 17:14 -0400, 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.
>> 
>> I have included links to both the mokutil [5] and shim [6] changes I
>> have made to support this new functionality.
> 
> How hard it is to self-compile shim and boot it with QEMU (I
> do not know even the GIT location of Shim)?

It is not hard, that is the setup I use for my testing.  Upstream shim 
is located here [1].  Or you can use my repo which contains the necessary
changes [2].

[1] https://github.com/rhboot/shim
[2] https://github.com/esnowberg/shim/tree/mokvars-v2