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

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Message-ID: <CAN5uoS8QCL+s2Kt0QSBAz4B84KWPKFhVYNG=+3T=rtdvK-jwEw@mail.gmail.com>
Date:   Wed, 10 May 2023 16:58:20 +0200
From:   Etienne Carriere <etienne.carriere@...aro.org>
To:     Sumit Garg <sumit.garg@...aro.org>
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

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.
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].

[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
> >