linux-kernel - Re: [RFC v2 0/6] Introduce TEE based Trusted Keys support

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Message-ID: <CAE=NcraDkm5cxE=ceq_9XkQz=NZ6KdVXkNUsdD4G2LrWz-bpDw@mail.gmail.com>
Date:   Thu, 1 Aug 2019 09:21:39 +0300
From:   Janne Karhunen <janne.karhunen@...il.com>
To:     Sumit Garg <sumit.garg@...aro.org>
Cc:     keyrings@...r.kernel.org, linux-integrity@...r.kernel.org,
        linux-security-module@...r.kernel.org,
        Jens Wiklander <jens.wiklander@...aro.org>,
        Jonathan Corbet <corbet@....net>, dhowells@...hat.com,
        jejb@...ux.ibm.com,
        Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>,
        Mimi Zohar <zohar@...ux.ibm.com>,
        James Morris <jmorris@...ei.org>,
        "Serge E. Hallyn" <serge@...lyn.com>,
        Casey Schaufler <casey@...aufler-ca.com>,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        Daniel Thompson <daniel.thompson@...aro.org>,
        Linux Doc Mailing List <linux-doc@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        "tee-dev @ lists . linaro . org" <tee-dev@...ts.linaro.org>
Subject: Re: [RFC v2 0/6] Introduce TEE based Trusted Keys support

On Wed, Jul 31, 2019 at 4:58 PM Sumit Garg <sumit.garg@...aro.org> wrote:

> > To clarify a bit further - my thought was to support any type of trust
> > source.
>
> That could be very well accomplished via Trusted Keys abstraction
> framework [1]. A trust source just need to implement following APIs:
>
> struct trusted_key_ops ts_trusted_key_ops = {
>        .migratable = 0, /* non-migratable */
>        .init = init_ts_trusted,
>        .seal = ts_key_seal,
>        .unseal = ts_key_unseal,
>        .get_random = ts_get_random,
>        .cleanup = cleanup_ts_trusted,
> };

Which is basically the same as implementing a new keytype in the
kernel; abstraction is not raised in any considerable manner this way?

I chose the userspace plugin due to this, you can use userspace aids
to provide any type of service. Use the crypto library you desire to
do the magic you want.


> > With the
> > user mode helper in between anyone can easily add their own thing in
> > there.
>
> Isn't actual purpose to have trusted keys is to protect user-space
> from access to kernel keys in plain format? Doesn't user mode helper
> defeat that purpose in one way or another?

Not really. CPU is in the user mode while running the code, but the
code or the secure keydata being is not available to the 'normal'
userspace. It's like microkernel service/driver this way. The usermode
driver is part of the kernel image and it runs on top of a invisible
rootfs.


--
Janne