linux-kernel - Re: [PATCHv2 2/2] tpm_ftpm_tee: register driver on TEE bus

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Message-ID: <20200528101150.GA156014@jade>
Date:   Thu, 28 May 2020 12:11:50 +0200
From:   Jens Wiklander <jens.wiklander@...aro.org>
To:     Maxim Uvarov <maxim.uvarov@...aro.org>
Cc:     Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        "tee-dev @ lists . linaro . org" <tee-dev@...ts.linaro.org>,
        peterhuewe@....de, Jason Gunthorpe <jgg@...pe.ca>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-integrity@...r.kernel.org, Arnd Bergmann <arnd@...aro.org>,
        Sumit Garg <sumit.garg@...aro.org>
Subject: Re: [PATCHv2 2/2] tpm_ftpm_tee: register driver on TEE bus

On Thu, May 28, 2020 at 11:08:18AM +0300, Maxim Uvarov wrote:
> On Wed, 27 May 2020 at 22:42, Jarkko Sakkinen
> <jarkko.sakkinen@...ux.intel.com> wrote:
> >
> > On Mon, 2020-05-25 at 09:50 +0300, Maxim Uvarov wrote:
> > > Jakko,
> > > tee-supplicant application provides state machine over callbacks with
> > > RPC messages.
> > > https://github.com/OP-TEE/optee_client/blob/master/tee-supplicant/src/tee_supplicant.c#L614
> > > It also allocates shm. Without running tee-supplicant
> > > tee_client_open_session() will fail.
> > > optee_open_session()->get_msg_arg()->tee_shm_alloc()->...
> > > Optee team wanted to remove some dependencies from tee-supplicant with
> > > moving code
> > > to the kernel. But for now I think that should be out of the scope of
> > > current patches due to
> > > they fix driver initialization on tee bus without breaking current
> > > functionality.
> >
> > So what is the role in high-level for tee-supplicant? Why does it
> > exist? No time to dive into code unfortunately.
> >
> 
> Original implementation for tee-supplicant does several things:
> 1. allocate shm
> 2. load ta from user space (fs file)
> 3. emulate rpmb
> 4. also there are some ftrace and socket functions which I did not use.
> 
> As I I understand, current implementation uses tee-supplicant and it's
> library as
> API from user land to Trusted OS.
> 
> Some docs can be found here:
> https://optee.readthedocs.io/en/latest/architecture/index.html
> 
> 
> 
> > These kernel commits do not explain in simple terms enough how all
> > of these entities connect with each other, if you don't have that
> > understanding beforehand.
> >
> 
> Yes, that is true. But I think it's something new and good docs will
> be some time later.

There's already some in Documentation/tee.txt, but it will get outdated
if we don't update it when we architectural changes like this. It's a
pity we missed updating it with the introduction of the bus. It seems a
good time to do it now so it easier to follow what's done.

Cheers,
Jens

> 
> > /Jarkko
> >
> 
> Regards,
> Maxim.