Re: [Tee-dev] [PATCH v2] drivers: optee: allow op-tee to access devices on the i2c bus

[Sumit Garg]

Hi Jorge,

On Mon, 1 Jun 2020 at 04:41, Jorge Ramirez-Ortiz <jorge@xxxxxxxxxxxx> wrote:
>
> Some secure elements like NXP's SE050 sit on I2C buses. For OP-TEE to
> control this type of cryptographic devices it needs coordinated access
> to the bus, so collisions and RUNTIME_PM dont get in the way.
>
> This trampoline driver allow OP-TEE to access them.
>

This sounds like an interesting use-case but I would like to
understand how secure is this communication interface with the secure
element? Like in the case of RPMB, secure world data is encrypted
which flows via tee-supplicant to RPMB device.

-Sumit

> Signed-off-by: Jorge Ramirez-Ortiz <jorge@xxxxxxxxxxxx>
> ---
>  drivers/tee/optee/optee_msg.h | 18 +++++++++++
>  drivers/tee/optee/rpc.c       | 57 +++++++++++++++++++++++++++++++++++
>  2 files changed, 75 insertions(+)
>
> diff --git a/drivers/tee/optee/optee_msg.h b/drivers/tee/optee/optee_msg.h
> index 795bc19ae17a..b6cc964fdeea 100644
> --- a/drivers/tee/optee/optee_msg.h
> +++ b/drivers/tee/optee/optee_msg.h
> @@ -419,4 +419,22 @@ struct optee_msg_arg {
>   */
>  #define OPTEE_MSG_RPC_CMD_SHM_FREE     7
>
> +/*
> + * Access a device on an i2c bus
> + *
> + * [in]  param[0].u.value.a            mode: RD(0), WR(1)
> + * [in]  param[0].u.value.b            i2c adapter
> + * [in]  param[0].u.value.c            i2c chip
> + *
> + * [io]  param[1].u.tmem.buf_ptr       physical address
> + * [io]  param[1].u.tmem.size          transfer size in bytes
> + * [io]  param[1].u.tmem.shm_ref       shared memory reference
> + *
> + * [out]  param[0].u.value.a           bytes transferred
> + *
> + */
> +#define OPTEE_MSG_RPC_CMD_I2C_TRANSFER 8
> +#define OPTEE_MSG_RPC_CMD_I2C_TRANSFER_RD 0
> +#define OPTEE_MSG_RPC_CMD_I2C_TRANSFER_WR 1
> +
>  #endif /* _OPTEE_MSG_H */
> diff --git a/drivers/tee/optee/rpc.c b/drivers/tee/optee/rpc.c
> index b4ade54d1f28..21d452805c6f 100644
> --- a/drivers/tee/optee/rpc.c
> +++ b/drivers/tee/optee/rpc.c
> @@ -9,6 +9,7 @@
>  #include <linux/device.h>
>  #include <linux/slab.h>
>  #include <linux/tee_drv.h>
> +#include <linux/i2c.h>
>  #include "optee_private.h"
>  #include "optee_smc.h"
>
> @@ -48,6 +49,59 @@ static void handle_rpc_func_cmd_get_time(struct optee_msg_arg *arg)
>  bad:
>         arg->ret = TEEC_ERROR_BAD_PARAMETERS;
>  }
> +static void handle_rpc_func_cmd_i2c_transfer(struct tee_context *ctx,
> +                                            struct optee_msg_arg *arg)
> +{
> +       struct i2c_client client;
> +       struct tee_shm *shm;
> +       int i, ret;
> +       char *buf;
> +       uint32_t attr[] = {
> +               OPTEE_MSG_ATTR_TYPE_VALUE_INPUT,
> +               OPTEE_MSG_ATTR_TYPE_TMEM_INOUT,
> +               OPTEE_MSG_ATTR_TYPE_VALUE_OUTPUT,
> +       };
> +
> +       if (arg->num_params != ARRAY_SIZE(attr))
> +               goto bad;
> +
> +       for (i = 0; i < ARRAY_SIZE(attr); i++)
> +               if ((arg->params[i].attr & OPTEE_MSG_ATTR_TYPE_MASK) != attr[i])
> +                       goto bad;
> +
> +       shm = (struct tee_shm *)(unsigned long)arg->params[1].u.tmem.shm_ref;
> +       buf = (char *)shm->kaddr;
> +
> +       client.addr = arg->params[0].u.value.c;
> +       client.adapter = i2c_get_adapter(arg->params[0].u.value.b);
> +       if (!client.adapter)
> +               goto bad;
> +
> +       snprintf(client.name, I2C_NAME_SIZE, "i2c%d", client.adapter->nr);
> +
> +       switch (arg->params[0].u.value.a) {
> +       case OPTEE_MSG_RPC_CMD_I2C_TRANSFER_RD:
> +               ret = i2c_master_recv(&client, buf, arg->params[1].u.tmem.size);
> +               break;
> +       case OPTEE_MSG_RPC_CMD_I2C_TRANSFER_WR:
> +               ret = i2c_master_send(&client, buf, arg->params[1].u.tmem.size);
> +               break;
> +       default:
> +               i2c_put_adapter(client.adapter);
> +               goto bad;
> +       }
> +
> +       if (ret >= 0) {
> +               arg->params[2].u.value.a = ret;
> +               arg->ret = TEEC_SUCCESS;
> +       } else
> +               arg->ret = TEEC_ERROR_COMMUNICATION;
> +
> +       i2c_put_adapter(client.adapter);
> +       return;
> +bad:
> +       arg->ret = TEEC_ERROR_BAD_PARAMETERS;
> +}
>
>  static struct wq_entry *wq_entry_get(struct optee_wait_queue *wq, u32 key)
>  {
> @@ -382,6 +436,9 @@ static void handle_rpc_func_cmd(struct tee_context *ctx, struct optee *optee,
>         case OPTEE_MSG_RPC_CMD_SHM_FREE:
>                 handle_rpc_func_cmd_shm_free(ctx, arg);
>                 break;
> +       case OPTEE_MSG_RPC_CMD_I2C_TRANSFER:
> +               handle_rpc_func_cmd_i2c_transfer(ctx, arg);
> +               break;
>         default:
>                 handle_rpc_supp_cmd(ctx, arg);
>         }
> --
> 2.17.1
>
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