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Subject: Re: [Tee-dev] [PATCH v5 2/2] tee: add private login method for kernel
 clients
To:     Sumit Garg <sumit.garg@linaro.org>
Cc:     Jens Wiklander <jens.wiklander@linaro.org>,
        "tee-dev @ lists . linaro . org" <tee-dev@lists.linaro.org>,
        Daniel Thompson <daniel.thompson@linaro.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
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 <CAFA6WYOvBNcGe+4ndq-YmM6haVoH4QiM7goYw5T40mR15muQKQ@mail.gmail.com>
From:   Jerome Forissier <jerome@forissier.org>
Message-ID: <b64c3ace-4558-deb5-7493-4837f48af188@forissier.org>
Date:   Thu, 26 Mar 2020 10:23:33 +0100
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On 3/26/20 10:07 AM, Sumit Garg wrote:
> On Thu, 26 Mar 2020 at 14:05, Jérôme Forissier <jerome@forissier.org> wrote:
>>
>> On Thu, Mar 26, 2020 at 8:24 AM Sumit Garg <sumit.garg@linaro.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.

(BTW sorry for my previous HTML reply)

-- 
Jerome
> 
> -Sumit
> 
>> --
>> Jerome
>>
>>>
>>>
>>> Signed-off-by: Sumit Garg <sumit.garg@linaro.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@lists.linaro.org
>>> https://lists.linaro.org/mailman/listinfo/tee-dev