linux-kernel - Re: [PATCH] char: tpm: ftpm_tee: use kernel login identifier

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Message-ID: <CAFA6WYNEmAdYZ6KpKYrFUuVPjHm=L7dF74d7tWE45DVZrJXqnA@mail.gmail.com>
Date:   Thu, 11 May 2023 13:35:11 +0530
From:   Sumit Garg <sumit.garg@...aro.org>
To:     Etienne Carriere <etienne.carriere@...aro.org>,
        Thirupathaiah Annapureddy <thiruan@...rosoft.com>
Cc:     linux-kernel@...r.kernel.org, Peter Huewe <peterhuewe@....de>,
        Jarkko Sakkinen <jarkko@...nel.org>,
        Jason Gunthorpe <jgg@...pe.ca>, linux-integrity@...r.kernel.org
Subject: Re: [PATCH] char: tpm: ftpm_tee: use kernel login identifier

+ Thirupathaiah (TEE fTPM driver author)

On Wed, 10 May 2023 at 20:28, Etienne Carriere
<etienne.carriere@...aro.org> wrote:
>
> Hello Sumit,
>
> On Wed, 10 May 2023 at 12:24, Sumit Garg <sumit.garg@...aro.org> wrote:
> >
> > Hi Etienne,
> >
> > On Sat, 6 May 2023 at 00:14, Etienne Carriere
> > <etienne.carriere@...aro.org> wrote:
> > >
> > > Changes fTPM TEE driver to open the TEE session with REE kernel login
> > > identifier rather than public login. This is needed in case fTPM service
> > > it denied to user land application and restricted to kernel operating
> > > system services only.
> >
> > This is a valid restriction to avoid any unintended use of fTPM by
> > user-space. But has the corresponding patch landed in fTPM TA which
> > would enforce this restriction?
>
> Not yet. Actually, I've posted some other change requests in the repo
> [1]  but got no feedback. Not nice from me but I didn't post any other
> changes since.

Hi Thirupathaiah,

Is there any plan to maintain fTPM OP-TEE TA going forward? As
otherwise users have to maintain downstream patches or forks.

> In the mean time, I think Linux kernel should be ready for this before
> fTPM implementation is fixed.
> Note that U-Boot already integrate this login identifier change, see [2].

Yeah you are right but without a corresponding reference fTPM TA, it
won't be possible to test this capability.

-Sumit

>
> [1] https://github.com/microsoft/ms-tpm-20-ref/pull/83
> [2] https://source.denx.de/u-boot/u-boot/-/commit/33ba80303e93869c439828dd289fb8ef64ed3bfc
>
> Best regards,
> Etienne
>
> >
> > -Sumit
> >
> > >
> > > Signed-off-by: Etienne Carriere <etienne.carriere@...aro.org>
> > > ---
> > >  drivers/char/tpm/tpm_ftpm_tee.c | 2 +-
> > >  1 file changed, 1 insertion(+), 1 deletion(-)
> > >
> > > diff --git a/drivers/char/tpm/tpm_ftpm_tee.c b/drivers/char/tpm/tpm_ftpm_tee.c
> > > index 528f35b14fb6..6d32e260af43 100644
> > > --- a/drivers/char/tpm/tpm_ftpm_tee.c
> > > +++ b/drivers/char/tpm/tpm_ftpm_tee.c
> > > @@ -241,7 +241,7 @@ static int ftpm_tee_probe(struct device *dev)
> > >         /* Open a session with fTPM TA */
> > >         memset(&sess_arg, 0, sizeof(sess_arg));
> > >         export_uuid(sess_arg.uuid, &ftpm_ta_uuid);
> > > -       sess_arg.clnt_login = TEE_IOCTL_LOGIN_PUBLIC;
> > > +       sess_arg.clnt_login = TEE_IOCTL_LOGIN_REE_KERNEL;
> > >         sess_arg.num_params = 0;
> > >
> > >         rc = tee_client_open_session(pvt_data->ctx, &sess_arg, NULL);
> > > --
> > > 2.25.1
> > >