tee: add private login method for kernel clients

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 GP implementation
defined login method range: (0x80000000 - 0xBFFFFFFF).
Reviewed-by: Jerome Forissier <jerome@forissier.org>
Signed-off-by: Sumit Garg <sumit.garg@linaro.org>
Signed-off-by: Jens Wiklander <jens.wiklander@linaro.org>

drivers/tee/tee_core.c

@@ -333,6 +333,13 @@ static int tee_ioctl_open_session(struct tee_context *ctx,
 			goto out;
 	}
 
+	if (arg.clnt_login >= TEE_IOCTL_LOGIN_REE_KERNEL_MIN &&
+	    arg.clnt_login <= TEE_IOCTL_LOGIN_REE_KERNEL_MAX) {
+		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;

include/uapi/linux/tee.h

@@ -173,6 +173,15 @@ 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 - 0xBFFFFFFF). This range is rather
+ * being reserved for REE kernel clients or TEE implementation.
+ */
+#define TEE_IOCTL_LOGIN_REE_KERNEL_MIN		0x80000000
+#define TEE_IOCTL_LOGIN_REE_KERNEL_MAX		0xBFFFFFFF
+/* Private login method for REE kernel clients */
+#define TEE_IOCTL_LOGIN_REE_KERNEL		0x80000000
 
 /**
  * struct tee_ioctl_param - parameter