linux-kernel - Re: [PATCH v2 1/2] security/keys/secure_key: Adds the secure key support based on CAAM.

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Date:   Thu, 02 Aug 2018 11:57:41 -0700
From:   James Bottomley <James.Bottomley@...senPartnership.com>
To:     David Howells <dhowells@...hat.com>,
        Udit Agarwal <udit.agarwal@....com>
Cc:     zohar@...ux.vnet.ibm.com, jmorris@...ei.org, serge@...lyn.com,
        denkenz@...il.com, linux-integrity@...r.kernel.org,
        keyrings@...r.kernel.org, linux-security-module@...r.kernel.org,
        linux-kernel@...r.kernel.org, sahil.malhotra@....com,
        ruchika.gupta@....com, horia.geanta@....com, aymen.sghaier@....com
Subject: Re: [PATCH v2 1/2] security/keys/secure_key: Adds the secure key
 support based on CAAM.

On Thu, 2018-08-02 at 17:14 +0100, David Howells wrote:
> Udit Agarwal <udit.agarwal@....com> wrote:
> 
> > +==========
> > +Secure Key
> > +==========
> > +
> > +Secure key is the new type added to kernel key ring service.
> > +Secure key is a symmetric type key of minimum length 32 bytes
> > +and with maximum possible length to be 128 bytes. It is produced
> > +in kernel using the CAAM crypto engine. Userspace can only see
> > +the blob for the corresponding key. All the blobs are displayed
> > +or loaded in hex ascii.
> 
> To echo Mimi, this sounds suspiciously like it should have a generic
> interface, not one that's specifically tied to one piece of hardware
> -
> particularly if it's named with generic "secure".
> 
> Can you convert this into a "symmetric" type and make the backend
> pluggable?

This is a symmetric key backed by a piece of hardware, which is exactly
what trusted keys are, so if we're defining common infrastructure with
callouts, trusted keys should be part of it.

Additionally, when I look at the trusted key code, I have significant
qualms about using the TPM RNG exclusively in the same way CAAM wants
to use its own RNG.  What I think both should be doing is collecting
data from their local RNGs, mixing it into the kernel entropy pool and
using a kernel generated random number (just in case these RNGs
suddenly turn out to be less random than they should be).

James