linux-kernel - Re: [RFC 3/7] tee: add private login method for kernel clients

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Message-ID: <20190708153908.GA28253@jax>
Date:   Mon, 8 Jul 2019 17:39:09 +0200
From:   Jens Wiklander <jens.wiklander@...aro.org>
To:     Sumit Garg <sumit.garg@...aro.org>
Cc:     keyrings@...r.kernel.org, linux-integrity@...r.kernel.org,
        linux-security-module@...r.kernel.org, corbet@....net,
        dhowells@...hat.com, jejb@...ux.ibm.com,
        jarkko.sakkinen@...ux.intel.com, zohar@...ux.ibm.com,
        jmorris@...ei.org, serge@...lyn.com, ard.biesheuvel@...aro.org,
        daniel.thompson@...aro.org, linux-doc@...r.kernel.org,
        linux-kernel@...r.kernel.org, tee-dev@...ts.linaro.org
Subject: Re: [RFC 3/7] tee: add private login method for kernel clients

Hi Sumit,

On Thu, Jun 13, 2019 at 04:00:29PM +0530, Sumit Garg 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 and disallow user-space to open-session using this login method.
> 
> Signed-off-by: Sumit Garg <sumit.garg@...aro.org>
> ---
>  drivers/tee/tee_core.c   | 6 ++++++
>  include/uapi/linux/tee.h | 2 ++
>  2 files changed, 8 insertions(+)
> 
> diff --git a/drivers/tee/tee_core.c b/drivers/tee/tee_core.c
> index 0f16d9f..4581bd1 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_REE_KERNEL) {
TEE_IOCTL_LOGIN_REE_KERNEL is defined as 0x80000000 which is in the
range specified and implementation defined by the GP spec. I wonder if
we shouldn't filter the entire implementation defined range instead of
just this value.

> +		pr_err("login method not allowed for user-space client\n");
pr_debug(), if it's needed at all.

> +		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 4b9eb06..f33c69c 100644
> --- a/include/uapi/linux/tee.h
> +++ b/include/uapi/linux/tee.h
> @@ -172,6 +172,8 @@ 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
> +/* Private login method for REE kernel clients */
It's worth noting that this is filtered by the TEE framework, compared
to everything else which is treated opaquely.

> +#define TEE_IOCTL_LOGIN_REE_KERNEL		0x80000000
>  
>  /**
>   * struct tee_ioctl_param - parameter
> -- 
> 2.7.4
> 

Thanks,
Jens