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

[Sumit Garg]

On Thu, 26 Mar 2020 at 14:05, JÃrÃme Forissier <jerome@xxxxxxxxxxxxx> wrote:
>
> On Thu, Mar 26, 2020 at 8:24 AM Sumit Garg <sumit.garg@xxxxxxxxxx> 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/

-Sumit

> --
> Jerome
>
>>
>>
>> Signed-off-by: Sumit Garg <sumit.garg@xxxxxxxxxx>
>> ---
>>  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
>>
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