linux-kernel - Re: [PATCH 0/7] Add CA enforcement keyring restrictions

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Date:   Wed, 9 Nov 2022 09:58:26 -0500
From:   Elaine Palmer <erpalmer@...ux.vnet.ibm.com>
To:     Eric Snowberg <eric.snowberg@...cle.com>,
        jarkko Sakkinen <jarkko@...nel.org>,
        Mimi Zohar <zohar@...ux.ibm.com>,
        Elaine Palmer <erpalmerny@...il.com>
Cc:     Coiby Xu <coxu@...hat.com>,
        "davem@...emloft.net" <davem@...emloft.net>,
        David Howells <dhowells@...hat.com>,
        "dmitry.kasatkin@...il.com" <dmitry.kasatkin@...il.com>,
        "dwmw2@...radead.org" <dwmw2@...radead.org>,
        "herbert@...dor.apana.org.au" <herbert@...dor.apana.org.au>,
        "jmorris@...ei.org" <jmorris@...ei.org>,
        Konrad Wilk <konrad.wilk@...cle.com>,
        Kanth Ghatraju <kanth.ghatraju@...cle.com>,
        "keyrings@...r.kernel.org" <keyrings@...r.kernel.org>,
        "linux-crypto@...r.kernel.org" <linux-crypto@...r.kernel.org>,
        "linux-integrity@...r.kernel.org" <linux-integrity@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-security-module@...r.kernel.org" 
        <linux-security-module@...r.kernel.org>,
        Lakshmi Ramasubramanian <nramas@...ux.microsoft.com>,
        "pvorel@...e.cz" <pvorel@...e.cz>,
        Roberto Sassu <roberto.sassu@...wei.com>,
        "serge@...lyn.com" <serge@...lyn.com>,
        "tiwai@...e.de" <tiwai@...e.de>,
        "erpalmer@...ux.ibm.com" <erpalmer@...ux.ibm.com>
Subject: Re: [PATCH 0/7] Add CA enforcement keyring restrictions



On 2022/11/09 9:25 AM, Eric Snowberg wrote:
>
>> On Nov 8, 2022, at 6:24 PM, Elaine Palmer <erpalmerny@...il.com> wrote:
>>
>>
>>
>> On 2022/11/04 9:20 AM, Coiby Xu wrote:
>>> Hi Eric,
>>>
>>> I wonder if there is any update on this work? I would be glad to do
>>> anything that may be helpful including testing a new version of code.
>>>
>> Hi Coiby,
>>
>> Yes, this discussion got stuck when we couldn't agree on one of the
>> following options:
>>
>> (A) Filter which keys from MOK (or a management system) are loaded
>>     onto the .machine keyring. Specifically, load only keys with
>>     CA+keyCertSign attributes.
>>
>> (B) Load all keys from MOK (or a management system) onto the
>>     .machine keyring. Then, subsequently filter those to restrict
>>     which ones can be loaded onto the .ima keyring specifically.
>>
>> The objection to (A) was that distros would have to go through
>> two steps instead of one to load keys. The one-step method of
>> loading keys was supported by an out-of-tree patch and then by
>> the addition of the .machine keyring.
>>
>> The objection to (B) was that, because the .machine keyring is now
>> linked to the .secondary keyring, it expands the scope of what the
>> kernel has trusted in the past. The effect is that keys in MOK
>> have the same broad scope as keys previously restricted to
>> .builtin and .secondary. It doesn't affect just IMA, but the rest
>> of the kernel as well.
>>
>> I would suggest that we can get unstuck by considering:
>>
>> (C) Defining a systemd (or dracut module) to load keys onto the
>>     .secondary keyring
>>
>> (D) Using a configuration option to specify what types of
>>     .machine keys should be allowed to pass through to the
>>     .secondary keyring.
>>    
>>     The distro could choose (A) by allowing only
>>     CA+keyCertSign keys.
>>
>>     The distro could choose (B) by allowing any kind
>>     of key.
>>
>> We all seemed to agree that enforcing key usage should be
>> implemented and that a useful future effort is to add policies
>> to keys and keyrings, like, "This key can only be used for
>> verifying kernel modules."
>>
>> I hope we can come to an agreement so work can proceed and IMA
>> can be re-enabled.
> I would be open to making the changes necessary to support both (A and B) 
> options.  What type of configuration option would be considered?  Would this 
> be a compile time Kconfig, a Linux boot command line parameter, or another 
> MOK variable?
>
Thank you, Eric.  A compile time Kconfig would be the most secure, yet
would still support (B) when allowed.