Message-ID: <aAYhCg6XOeZm7jqq@sumit-X1>
Date: Mon, 21 Apr 2025 16:12:18 +0530
From: Sumit Garg <sumit.garg@...nel.org>
To: Amirreza Zarrabi <amirreza.zarrabi@....qualcomm.com>
Cc: Jens Wiklander <jens.wiklander@...aro.org>,
	Bjorn Andersson <andersson@...nel.org>,
	Konrad Dybcio <konradybcio@...nel.org>,
	Bartosz Golaszewski <bartosz.golaszewski@...aro.org>,
	Apurupa Pattapu <quic_apurupa@...cinc.com>,
	Kees Cook <kees@...nel.org>,
	"Gustavo A. R. Silva" <gustavoars@...nel.org>,
	Sumit Semwal <sumit.semwal@...aro.org>,
	Christian König <christian.koenig@....com>,
	linux-arm-msm@...r.kernel.org, op-tee@...ts.trustedfirmware.org,
	linux-kernel@...r.kernel.org, linux-hardening@...r.kernel.org,
	dri-devel@...ts.freedesktop.org, linaro-mm-sig@...ts.linaro.org,
	linux-doc@...r.kernel.org
Subject: Re: [PATCH v3 02/11] tee: add close_context to TEE driver operation

On Thu, Mar 27, 2025 at 07:47:24PM -0700, Amirreza Zarrabi wrote:
> The tee_context can be used to manage TEE user resources, including
> those allocated by the driver for the TEE on behalf of the user.
> The release() callback is invoked only when all resources, such as
> tee_shm, are released and there are no references to the tee_context.
> 
> When a user closes the device file, the driver should notify the
> TEE to release any resources it may hold and drop the context
> references. To achieve this, a close_context() callback is
> introduced to initiate resource release in the TEE driver when
> the device file is closed.

Can you ellaborate more as to whether the TEE driver will release
resources corresponding to a particular user or all the users?

> 
> Relocate teedev_ctx_get, teedev_ctx_put, tee_device_get, and
> tee_device_get functions to tee_drv.h to make them accessible
> outside the TEE subsystem.

These should rather be relocated to tee_core.h as tee_drv.h is rather
meant for kernel TEE client drivers.

> 
> Signed-off-by: Amirreza Zarrabi <amirreza.zarrabi@....qualcomm.com>
> ---
>  drivers/tee/tee_core.c    | 39 +++++++++++++++++++++++++++++++++++++++
>  drivers/tee/tee_private.h |  6 ------
>  include/linux/tee_core.h  | 11 +++++++++--
>  include/linux/tee_drv.h   | 40 ++++++++++++++++++++++++++++++++++++++++
>  4 files changed, 88 insertions(+), 8 deletions(-)
> 
> diff --git a/drivers/tee/tee_core.c b/drivers/tee/tee_core.c
> index 24edce4cdbaa..22cc7d624b0c 100644
> --- a/drivers/tee/tee_core.c
> +++ b/drivers/tee/tee_core.c
> @@ -72,6 +72,20 @@ struct tee_context *teedev_open(struct tee_device *teedev)
>  }
>  EXPORT_SYMBOL_GPL(teedev_open);
>  
> +/**
> + * teedev_ctx_get() - Increment the reference count of a context
> + *
> + * This function increases the refcount of the context, which is tied to
> + * resources shared by the same tee_device. During the unregistration process,
> + * the context may remain valid even after tee_device_unregister() has returned.
> + *
> + * Users should ensure that the context's refcount is properly decreased before
> + * calling tee_device_put(), typically within the context's release() function.
> + * Alternatively, users can call tee_device_get() and teedev_ctx_get() together
> + * and release them simultaneously (see shm_alloc_helper()).
> + *
> + * @ctx: Pointer to the context
> + */

Let's not duplicate the documentation here when it has already been
documented in the header file.

Same for other places below.

-Sumit

>  void teedev_ctx_get(struct tee_context *ctx)
>  {
>  	if (ctx->releasing)
> @@ -79,6 +93,7 @@ void teedev_ctx_get(struct tee_context *ctx)
>  
>  	kref_get(&ctx->refcount);
>  }
> +EXPORT_SYMBOL_GPL(teedev_ctx_get);
>  
>  static void teedev_ctx_release(struct kref *ref)
>  {
> @@ -89,6 +104,10 @@ static void teedev_ctx_release(struct kref *ref)
>  	kfree(ctx);
>  }
>  
> +/**
> + * teedev_ctx_put() - Decrease reference count on a context
> + * @ctx: pointer to the context
> + */
>  void teedev_ctx_put(struct tee_context *ctx)
>  {
>  	if (ctx->releasing)
> @@ -96,11 +115,15 @@ void teedev_ctx_put(struct tee_context *ctx)
>  
>  	kref_put(&ctx->refcount, teedev_ctx_release);
>  }
> +EXPORT_SYMBOL_GPL(teedev_ctx_put);
>  
>  void teedev_close_context(struct tee_context *ctx)
>  {
>  	struct tee_device *teedev = ctx->teedev;
>  
> +	if (teedev->desc->ops->close_context)
> +		teedev->desc->ops->close_context(ctx);
> +
>  	teedev_ctx_put(ctx);
>  	tee_device_put(teedev);
>  }
> @@ -1024,6 +1047,10 @@ int tee_device_register(struct tee_device *teedev)
>  }
>  EXPORT_SYMBOL_GPL(tee_device_register);
>  
> +/**
> + * tee_device_put() - Decrease the user count for a tee_device
> + * @teedev: pointer to the tee_device
> + */
>  void tee_device_put(struct tee_device *teedev)
>  {
>  	mutex_lock(&teedev->mutex);
> @@ -1037,7 +1064,18 @@ void tee_device_put(struct tee_device *teedev)
>  	}
>  	mutex_unlock(&teedev->mutex);
>  }
> +EXPORT_SYMBOL_GPL(tee_device_put);
>  
> +/**
> + * tee_device_get() - Increment the user count for a tee_device
> + * @teedev: Pointer to the tee_device
> + *
> + * If tee_device_unregister() has been called and the final user of @teedev
> + * has already released the device, this function will fail to prevent new users
> + * from accessing the device during the unregistration process.
> + *
> + * Returns: true if @teedev remains valid, otherwise false
> + */
>  bool tee_device_get(struct tee_device *teedev)
>  {
>  	mutex_lock(&teedev->mutex);
> @@ -1049,6 +1087,7 @@ bool tee_device_get(struct tee_device *teedev)
>  	mutex_unlock(&teedev->mutex);
>  	return true;
>  }
> +EXPORT_SYMBOL_GPL(tee_device_get);
>  
>  /**
>   * tee_device_unregister() - Removes a TEE device
> diff --git a/drivers/tee/tee_private.h b/drivers/tee/tee_private.h
> index 9bc50605227c..d3f40a03de36 100644
> --- a/drivers/tee/tee_private.h
> +++ b/drivers/tee/tee_private.h
> @@ -14,12 +14,6 @@
>  
>  int tee_shm_get_fd(struct tee_shm *shm);
>  
> -bool tee_device_get(struct tee_device *teedev);
> -void tee_device_put(struct tee_device *teedev);
> -
> -void teedev_ctx_get(struct tee_context *ctx);
> -void teedev_ctx_put(struct tee_context *ctx);
> -
>  struct tee_shm *tee_shm_alloc_user_buf(struct tee_context *ctx, size_t size);
>  struct tee_shm *tee_shm_register_user_buf(struct tee_context *ctx,
>  					  unsigned long addr, size_t length);
> diff --git a/include/linux/tee_core.h b/include/linux/tee_core.h
> index a38494d6b5f4..8a4c9e30b652 100644
> --- a/include/linux/tee_core.h
> +++ b/include/linux/tee_core.h
> @@ -65,8 +65,9 @@ struct tee_device {
>  /**
>   * struct tee_driver_ops - driver operations vtable
>   * @get_version:	returns version of driver
> - * @open:		called when the device file is opened
> - * @release:		release this open file
> + * @open:		called for a context when the device file is opened
> + * @close_context:	called when the device file is closed
> + * @release:		called to release the context
>   * @open_session:	open a new session
>   * @close_session:	close a session
>   * @system_session:	declare session as a system session
> @@ -76,11 +77,17 @@ struct tee_device {
>   * @supp_send:		called for supplicant to send a response
>   * @shm_register:	register shared memory buffer in TEE
>   * @shm_unregister:	unregister shared memory buffer in TEE
> + *
> + * The context given to @open might last longer than the device file if it is
> + * tied to other resources in the TEE driver. @close_context is called when the
> + * client closes the device file, even if there are existing references to the
> + * context. The TEE driver can use @close_context to start cleaning up.
>   */
>  struct tee_driver_ops {
>  	void (*get_version)(struct tee_device *teedev,
>  			    struct tee_ioctl_version_data *vers);
>  	int (*open)(struct tee_context *ctx);
> +	void (*close_context)(struct tee_context *ctx);
>  	void (*release)(struct tee_context *ctx);
>  	int (*open_session)(struct tee_context *ctx,
>  			    struct tee_ioctl_open_session_arg *arg,
> diff --git a/include/linux/tee_drv.h b/include/linux/tee_drv.h
> index a54c203000ed..ce23fd42c5d4 100644
> --- a/include/linux/tee_drv.h
> +++ b/include/linux/tee_drv.h
> @@ -96,6 +96,46 @@ struct tee_param {
>  	} u;
>  };
>  
> +/**
> + * tee_device_get() - Increment the user count for a tee_device
> + * @teedev: Pointer to the tee_device
> + *
> + * If tee_device_unregister() has been called and the final user of @teedev
> + * has already released the device, this function will fail to prevent new users
> + * from accessing the device during the unregistration process.
> + *
> + * Returns: true if @teedev remains valid, otherwise false
> + */
> +bool tee_device_get(struct tee_device *teedev);
> +
> +/**
> + * tee_device_put() - Decrease the user count for a tee_device
> + * @teedev: pointer to the tee_device
> + */
> +void tee_device_put(struct tee_device *teedev);
> +
> +/**
> + * teedev_ctx_get() - Increment the reference count of a context
> + *
> + * This function increases the refcount of the context, which is tied to
> + * resources shared by the same tee_device. During the unregistration process,
> + * the context may remain valid even after tee_device_unregister() has returned.
> + *
> + * Users should ensure that the context's refcount is properly decreased before
> + * calling tee_device_put(), typically within the context's release() function.
> + * Alternatively, users can call tee_device_get() and teedev_ctx_get() together
> + * and release them simultaneously (see shm_alloc_helper()).
> + *
> + * @ctx: Pointer to the context
> + */
> +void teedev_ctx_get(struct tee_context *ctx);
> +
> +/**
> + * teedev_ctx_put() - Decrease reference count on a context
> + * @ctx: pointer to the context
> + */
> +void teedev_ctx_put(struct tee_context *ctx);
> +
>  /**
>   * tee_shm_alloc_kernel_buf() - Allocate kernel shared memory for a
>   *                              particular TEE client driver
> 
> -- 
> 2.34.1
> 
> 

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