linux-kernel - Re: [Tee-dev] [PATCH v5 2/2] tee: add private login method for kernel clients

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Message-ID: <CAFA6WYOGPNOyWU3Y+ipAo_FGioTnRkdmURc7H1FM1ENe_dfQXg@mail.gmail.com>
Date:   Thu, 26 Mar 2020 15:09:08 +0530
From:   Sumit Garg <sumit.garg@...aro.org>
To:     Jerome Forissier <jerome@...issier.org>
Cc:     Jens Wiklander <jens.wiklander@...aro.org>,
        "tee-dev @ lists . linaro . org" <tee-dev@...ts.linaro.org>,
        Daniel Thompson <daniel.thompson@...aro.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [Tee-dev] [PATCH v5 2/2] tee: add private login method for kernel clients

On Thu, 26 Mar 2020 at 14:53, Jerome Forissier <jerome@...issier.org> wrote:
>
> On 3/26/20 10:07 AM, Sumit Garg wrote:
> > On Thu, 26 Mar 2020 at 14:05, Jérôme Forissier <jerome@...issier.org> wrote:
> >>
> >> On Thu, Mar 26, 2020 at 8:24 AM Sumit Garg <sumit.garg@...aro.org> wrote:
> >>>
> >>> There are use-cases where user-space shouldn't be allowed to communicate
> >>> directly with a TEE device which is dedicated to provide a specific
> >>> service for a kernel client. So add a private login method for kernel
> >>> clients
> >>
> >>
> >> OK
> >>
> >>> and disallow user-space to open-session using GP implementation
> >>> defined login method range: (0x80000000 - 0xFFFFFFFF).
> >>
> >>
> >> I'm not sure this is correct, because it would prevent the client library or the TEE supplicant from using such values, although they are part of the TEE implementation; and further, nothing mandates that an implementation-defined method should not be used directly by client applications.
> >>
> >
> > Initial implementation of this patch only put restriction for single
> > implementation-defined login method (TEE_IOCTL_LOGIN_REE_KERNEL) only.
> > But after discussion with Jens here [1], I have changed that to
> > restrict complete implementation-defined range. If we think to further
> > partition this range considering API stability then I am open to that
> > too.
> >
> > [1] https://lore.kernel.org/patchwork/patch/1088062/
>
> In the end he proposed to reserve half the range for user space and half
> for kernel space.

It seems I probably misunderstood his proposal. So let me reserve
(0x80000000 - 0xBFFFFFFF) range for kernel space.

>
> (BTW sorry for my previous HTML reply)
>

No worries.

-Sumit

> --
> Jerome
> >
> > -Sumit
> >
> >> --
> >> Jerome
> >>
> >>>
> >>>
> >>> Signed-off-by: Sumit Garg <sumit.garg@...aro.org>
> >>> ---
> >>>  drivers/tee/tee_core.c   | 6 ++++++
> >>>  include/uapi/linux/tee.h | 8 ++++++++
> >>>  2 files changed, 14 insertions(+)
> >>>
> >>> diff --git a/drivers/tee/tee_core.c b/drivers/tee/tee_core.c
> >>> index 37d22e3..533e7a8 100644
> >>> --- a/drivers/tee/tee_core.c
> >>> +++ b/drivers/tee/tee_core.c
> >>> @@ -334,6 +334,12 @@ static int tee_ioctl_open_session(struct tee_context *ctx,
> >>>                         goto out;
> >>>         }
> >>>
> >>> +       if (arg.clnt_login & TEE_IOCTL_LOGIN_MASK) {
> >>> +               pr_debug("login method not allowed for user-space client\n");
> >>> +               rc = -EPERM;
> >>> +               goto out;
> >>> +       }
> >>> +
> >>>         rc = ctx->teedev->desc->ops->open_session(ctx, &arg, params);
> >>>         if (rc)
> >>>                 goto out;
> >>> diff --git a/include/uapi/linux/tee.h b/include/uapi/linux/tee.h
> >>> index 6596f3a..19172a2 100644
> >>> --- a/include/uapi/linux/tee.h
> >>> +++ b/include/uapi/linux/tee.h
> >>> @@ -173,6 +173,14 @@ struct tee_ioctl_buf_data {
> >>>  #define TEE_IOCTL_LOGIN_APPLICATION            4
> >>>  #define TEE_IOCTL_LOGIN_USER_APPLICATION       5
> >>>  #define TEE_IOCTL_LOGIN_GROUP_APPLICATION      6
> >>> +/*
> >>> + * Disallow user-space to use GP implementation specific login
> >>> + * method range (0x80000000 - 0xFFFFFFFF). This range is rather
> >>> + * being reserved for REE kernel clients or TEE implementation.
> >>> + */
> >>> +#define TEE_IOCTL_LOGIN_MASK                   0x80000000
> >>> +/* Private login method for REE kernel clients */
> >>> +#define TEE_IOCTL_LOGIN_REE_KERNEL             0x80000000
> >>>
> >>>  /**
> >>>   * struct tee_ioctl_param - parameter
> >>> --
> >>> 2.7.4
> >>>
> >>> _______________________________________________
> >>> Tee-dev mailing list
> >>> Tee-dev@...ts.linaro.org
> >>> https://lists.linaro.org/mailman/listinfo/tee-dev

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