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

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Date:   Wed, 9 Nov 2022 14:25:08 +0000
From:   Eric Snowberg <eric.snowberg@...cle.com>
To:     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>, Mimi Zohar <zohar@...ux.ibm.com>,
        "erpalmer@...ux.ibm.com" <erpalmer@...ux.ibm.com>
Subject: Re: [PATCH 0/7] Add CA enforcement keyring restrictions



> 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?