linux-kernel - Re: [PATCH v4 00/12] Enroll kernel keys thru MOK

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Date:   Tue, 31 Aug 2021 20:52:16 -0400
From:   Nayna <nayna@...ux.vnet.ibm.com>
To:     Eric Snowberg <eric.snowberg@...cle.com>,
        Mimi Zohar <zohar@...ux.ibm.com>
Cc:     James Bottomley <James.Bottomley@...senPartnership.com>,
        Jarkko Sakkinen <jarkko@...nel.org>,
        David Howells <dhowells@...hat.com>, keyrings@...r.kernel.org,
        linux-integrity <linux-integrity@...r.kernel.org>,
        David Woodhouse <dwmw2@...radead.org>,
        Herbert Xu <herbert@...dor.apana.org.au>,
        "David S . Miller" <davem@...emloft.net>,
        James Morris <jmorris@...ei.org>,
        "Serge E . Hallyn" <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,
        Lakshmi Ramasubramanian <nramas@...ux.microsoft.com>,
        lszubowi@...hat.com, linux-kernel@...r.kernel.org,
        linux-crypto@...r.kernel.org,
        linux-security-module@...r.kernel.org, pjones@...hat.com,
        "konrad.wilk@...cle.com" <konrad.wilk@...cle.com>,
        Patrick Uiterwijk <patrick@...terwijk.org>
Subject: Re: [PATCH v4 00/12] Enroll kernel keys thru MOK


On 8/30/21 1:39 PM, Eric Snowberg wrote:
>> On Aug 27, 2021, at 2:44 PM, Nayna <nayna@...ux.vnet.ibm.com> wrote:
>> On 8/25/21 6:27 PM, James Bottomley wrote:
>>> Remember, a CA cert is a self signed cert with the CA:TRUE basic
>>> constraint.  Pretty much no secure boot key satisfies this (secure boot
>>> chose deliberately NOT to use CA certificates, so they're all some type
>>> of intermediate or leaf), so the design seems to be only to pick out
>>> the CA certificates you put in the MOK keyring.  Adding the _ca suffix
>>> may deflect some of the "why aren't all my MOK certificates in the
>>> keyring" emails ...
>>
>> My understanding is the .system_ca keyring should not be restricted only
>> to self-signed CAs (Root CA). Any cert that can qualify as Root or
>> Intermediate CA with Basic Constraints CA:TRUE should be allowed. In
>> fact, the intermediate CA certificates closest to the leaf nodes would be
>> best.
> With an intermediate containing CA:TRUE, the intermediate cert would not
> be self signed. Just for my clarification, does this mean I should remove
> the check that validates if it is self signed and instead somehow check if
> the CA flag is set?  Wouldn’t this potentially allow improperly signed certs
> into this new keyring?
>
In this model, we are relying on the admin to ensure the authenticity of 
the certificate(s) being loaded onto the new keyring. It is similar to 
trusting the admin to enable the variable and add keys to MOK. Following 
are the checks that must pass before adding it to .system_ca keyring.

1. Check against revocation_list.
2. Check Basic Constraints: CA=TRUE.
3. Check keyUsage = keyCertSign.

Thanks & Regards,

        - Nayna