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Commit 1793126f authored by David Herrmann's avatar David Herrmann Committed by Dave Airlie
Browse files

drm: implement experimental render nodes 



Render nodes provide an API for userspace to use non-privileged GPU
commands without any running DRM-Master. It is useful for offscreen
rendering, GPGPU clients, and normal render clients which do not perform
modesetting.

Compared to legacy clients, render clients no longer need any
authentication to perform client ioctls. Instead, user-space controls
render/client access to GPUs via filesystem access-modes on the
render-node. Once a render-node was opened, a client has full access to
the client/render operations on the GPU. However, no modesetting or ioctls
that affect global state are allowed on render nodes.

To prevent privilege-escalation, drivers must explicitly state that they
support render nodes. They must mark their render-only ioctls as
DRM_RENDER_ALLOW so render clients can use them. Furthermore, they must
support clients without any attached master.

If filesystem access-modes are not enough for fine-grained access control
to render nodes (very unlikely, considering the versaitlity of FS-ACLs),
you may still fall-back to fd-passing from server to client (which allows
arbitrary access-control). However, note that revoking access is
currently impossible and unlikely to get implemented.

Note: Render clients no longer have any associated DRM-Master as they are
supposed to be independent of any server state. DRM core highly depends on
file_priv->master to be non-NULL for modesetting/ctx/etc. commands.
Therefore, drivers must be very careful to not require DRM-Master if they
support DRIVER_RENDER.

So far render-nodes are protected by "drm_rnodes". As long as this
module-parameter is not set to 1, a driver will not create render nodes.
This allows us to experiment with the API a bit before we stabilize it.

v2: drop insecure GEM_FLINK to force use of dmabuf

Signed-off-by: default avatarDavid Herrmann <dh.herrmann@gmail.com>
Signed-off-by: default avatarDave Airlie <airlied@redhat.com>
parent 6cb3b7f1

Documentation/DocBook/drm.tmpl

+69 −0
Original line number Diff line number Diff line
@@ -205,6 +205,12 @@ 
              Driver implements DRM PRIME buffer sharing.

            </para></listitem>

          </varlistentry>

          <varlistentry>

            <term>DRIVER_RENDER</term>

            <listitem><para>

              Driver supports dedicated render nodes.

            </para></listitem>

          </varlistentry>

        </variablelist>

      </sect3>

      <sect3>
@@ -2644,6 +2650,69 @@ int (*resume) (struct drm_device *);</synopsis> 
      info, since man pages should cover the rest.

    </para>



  <!-- External: render nodes -->



    <sect1>

      <title>Render nodes</title>

      <para>

        DRM core provides multiple character-devices for user-space to use.

        Depending on which device is opened, user-space can perform a different

        set of operations (mainly ioctls). The primary node is always created

        and called <term>card&lt;num&gt;</term>. Additionally, a currently

        unused control node, called <term>controlD&lt;num&gt;</term> is also

        created. The primary node provides all legacy operations and

        historically was the only interface used by userspace. With KMS, the

        control node was introduced. However, the planned KMS control interface

        has never been written and so the control node stays unused to date.

      </para>

      <para>

        With the increased use of offscreen renderers and GPGPU applications,

        clients no longer require running compositors or graphics servers to

        make use of a GPU. But the DRM API required unprivileged clients to

        authenticate to a DRM-Master prior to getting GPU access. To avoid this

        step and to grant clients GPU access without authenticating, render

        nodes were introduced. Render nodes solely serve render clients, that

        is, no modesetting or privileged ioctls can be issued on render nodes.

        Only non-global rendering commands are allowed. If a driver supports

        render nodes, it must advertise it via the <term>DRIVER_RENDER</term>

        DRM driver capability. If not supported, the primary node must be used

        for render clients together with the legacy drmAuth authentication

        procedure.

      </para>

      <para>

        If a driver advertises render node support, DRM core will create a

        separate render node called <term>renderD&lt;num&gt;</term>. There will

        be one render node per device. No ioctls except  PRIME-related ioctls

        will be allowed on this node. Especially <term>GEM_OPEN</term> will be

        explicitly prohibited. Render nodes are designed to avoid the

        buffer-leaks, which occur if clients guess the flink names or mmap

        offsets on the legacy interface. Additionally to this basic interface,

        drivers must mark their driver-dependent render-only ioctls as

        <term>DRM_RENDER_ALLOW</term> so render clients can use them. Driver

        authors must be careful not to allow any privileged ioctls on render

        nodes.

      </para>

      <para>

        With render nodes, user-space can now control access to the render node

        via basic file-system access-modes. A running graphics server which

        authenticates clients on the privileged primary/legacy node is no longer

        required. Instead, a client can open the render node and is immediately

        granted GPU access. Communication between clients (or servers) is done

        via PRIME. FLINK from render node to legacy node is not supported. New

        clients must not use the insecure FLINK interface.

      </para>

      <para>

        Besides dropping all modeset/global ioctls, render nodes also drop the

        DRM-Master concept. There is no reason to associate render clients with

        a DRM-Master as they are independent of any graphics server. Besides,

        they must work without any running master, anyway.

        Drivers must be able to run without a master object if they support

        render nodes. If, on the other hand, a driver requires shared state

        between clients which is visible to user-space and accessible beyond

        open-file boundaries, they cannot support render nodes.

      </para>

    </sect1>



  <!-- External: vblank handling -->



    <sect1>

drivers/gpu/drm/drm_drv.c

+7 −6
Original line number Diff line number Diff line
@@ -68,7 +68,7 @@ static const struct drm_ioctl_desc drm_ioctls[] = { 
	DRM_IOCTL_DEF(DRM_IOCTL_GET_MAP, drm_getmap, DRM_UNLOCKED),

	DRM_IOCTL_DEF(DRM_IOCTL_GET_CLIENT, drm_getclient, DRM_UNLOCKED),

	DRM_IOCTL_DEF(DRM_IOCTL_GET_STATS, drm_getstats, DRM_UNLOCKED),

	DRM_IOCTL_DEF(DRM_IOCTL_GET_CAP, drm_getcap, DRM_UNLOCKED),

	DRM_IOCTL_DEF(DRM_IOCTL_GET_CAP, drm_getcap, DRM_UNLOCKED|DRM_RENDER_ALLOW),

	DRM_IOCTL_DEF(DRM_IOCTL_SET_VERSION, drm_setversion, DRM_MASTER),



	DRM_IOCTL_DEF(DRM_IOCTL_SET_UNIQUE, drm_setunique, DRM_AUTH|DRM_MASTER|DRM_ROOT_ONLY),
@@ -130,14 +130,14 @@ static const struct drm_ioctl_desc drm_ioctls[] = { 


	DRM_IOCTL_DEF(DRM_IOCTL_UPDATE_DRAW, drm_noop, DRM_AUTH|DRM_MASTER|DRM_ROOT_ONLY),



	DRM_IOCTL_DEF(DRM_IOCTL_GEM_CLOSE, drm_gem_close_ioctl, DRM_UNLOCKED),

	DRM_IOCTL_DEF(DRM_IOCTL_GEM_CLOSE, drm_gem_close_ioctl, DRM_UNLOCKED|DRM_RENDER_ALLOW),

	DRM_IOCTL_DEF(DRM_IOCTL_GEM_FLINK, drm_gem_flink_ioctl, DRM_AUTH|DRM_UNLOCKED),

	DRM_IOCTL_DEF(DRM_IOCTL_GEM_OPEN, drm_gem_open_ioctl, DRM_AUTH|DRM_UNLOCKED),



	DRM_IOCTL_DEF(DRM_IOCTL_MODE_GETRESOURCES, drm_mode_getresources, DRM_CONTROL_ALLOW|DRM_UNLOCKED),



	DRM_IOCTL_DEF(DRM_IOCTL_PRIME_HANDLE_TO_FD, drm_prime_handle_to_fd_ioctl, DRM_AUTH|DRM_UNLOCKED),

	DRM_IOCTL_DEF(DRM_IOCTL_PRIME_FD_TO_HANDLE, drm_prime_fd_to_handle_ioctl, DRM_AUTH|DRM_UNLOCKED),

	DRM_IOCTL_DEF(DRM_IOCTL_PRIME_HANDLE_TO_FD, drm_prime_handle_to_fd_ioctl, DRM_AUTH|DRM_UNLOCKED|DRM_RENDER_ALLOW),

	DRM_IOCTL_DEF(DRM_IOCTL_PRIME_FD_TO_HANDLE, drm_prime_fd_to_handle_ioctl, DRM_AUTH|DRM_UNLOCKED|DRM_RENDER_ALLOW),



	DRM_IOCTL_DEF(DRM_IOCTL_MODE_GETPLANERESOURCES, drm_mode_getplane_res, DRM_CONTROL_ALLOW|DRM_UNLOCKED),

	DRM_IOCTL_DEF(DRM_IOCTL_MODE_GETCRTC, drm_mode_getcrtc, DRM_CONTROL_ALLOW|DRM_UNLOCKED),
@@ -420,9 +420,10 @@ long drm_ioctl(struct file *filp, 
		DRM_DEBUG("no function\n");

		retcode = -EINVAL;

	} else if (((ioctl->flags & DRM_ROOT_ONLY) && !capable(CAP_SYS_ADMIN)) ||

		   ((ioctl->flags & DRM_AUTH) && !file_priv->authenticated) ||

		   ((ioctl->flags & DRM_AUTH) && !drm_is_render_client(file_priv) && !file_priv->authenticated) ||

		   ((ioctl->flags & DRM_MASTER) && !file_priv->is_master) ||

		   (!(ioctl->flags & DRM_CONTROL_ALLOW) && (file_priv->minor->type == DRM_MINOR_CONTROL))) {

		   (!(ioctl->flags & DRM_CONTROL_ALLOW) && (file_priv->minor->type == DRM_MINOR_CONTROL)) ||

		   (!(ioctl->flags & DRM_RENDER_ALLOW) && drm_is_render_client(file_priv))) {

		retcode = -EACCES;

	} else {

		if (cmd & (IOC_IN | IOC_OUT)) {

drivers/gpu/drm/drm_fops.c

+7 −7
Original line number Diff line number Diff line
@@ -262,10 +262,10 @@ static int drm_open_helper(struct inode *inode, struct file *filp, 
			goto out_prime_destroy;

	}





	/* if there is no current master make this fd it */

	/* if there is no current master make this fd it, but do not create

	 * any master object for render clients */

	mutex_lock(&dev->struct_mutex);

	if (!priv->minor->master) {

	if (!priv->minor->master && !drm_is_render_client(priv)) {

		/* create a new master */

		priv->minor->master = drm_master_create(priv->minor);

		if (!priv->minor->master) {
@@ -303,12 +303,11 @@ static int drm_open_helper(struct inode *inode, struct file *filp, 
				goto out_close;

			}

		}

		mutex_unlock(&dev->struct_mutex);

	} else {

	} else if (!drm_is_render_client(priv)) {

		/* get a reference to the master */

		priv->master = drm_master_get(priv->minor->master);

		mutex_unlock(&dev->struct_mutex);

	}

	mutex_unlock(&dev->struct_mutex);



	mutex_lock(&dev->struct_mutex);

	list_add(&priv->lhead, &dev->filelist);
@@ -478,6 +477,7 @@ int drm_release(struct inode *inode, struct file *filp) 
	iput(container_of(dev->dev_mapping, struct inode, i_data));



	/* drop the reference held my the file priv */

	if (file_priv->master)

		drm_master_put(&file_priv->master);

	file_priv->is_master = 0;

	list_del(&file_priv->lhead);

drivers/gpu/drm/drm_pci.c

+9 −0
Original line number Diff line number Diff line
@@ -354,6 +354,12 @@ int drm_get_pci_dev(struct pci_dev *pdev, const struct pci_device_id *ent, 
			goto err_g2;

	}



	if (drm_core_check_feature(dev, DRIVER_RENDER) && drm_rnodes) {

		ret = drm_get_minor(dev, &dev->render, DRM_MINOR_RENDER);

		if (ret)

			goto err_g21;

	}



	if ((ret = drm_get_minor(dev, &dev->primary, DRM_MINOR_LEGACY)))

		goto err_g3;
@@ -383,6 +389,9 @@ int drm_get_pci_dev(struct pci_dev *pdev, const struct pci_device_id *ent, 
err_g4:

	drm_put_minor(&dev->primary);

err_g3:

	if (dev->render)

		drm_put_minor(&dev->render);

err_g21:

	if (drm_core_check_feature(dev, DRIVER_MODESET))

		drm_put_minor(&dev->control);

err_g2:

drivers/gpu/drm/drm_platform.c

+9 −0
Original line number Diff line number Diff line
@@ -69,6 +69,12 @@ static int drm_get_platform_dev(struct platform_device *platdev, 
			goto err_g1;

	}



	if (drm_core_check_feature(dev, DRIVER_RENDER) && drm_rnodes) {

		ret = drm_get_minor(dev, &dev->render, DRM_MINOR_RENDER);

		if (ret)

			goto err_g11;

	}



	ret = drm_get_minor(dev, &dev->primary, DRM_MINOR_LEGACY);

	if (ret)

		goto err_g2;
@@ -100,6 +106,9 @@ static int drm_get_platform_dev(struct platform_device *platdev, 
err_g3:

	drm_put_minor(&dev->primary);

err_g2:

	if (dev->render)

		drm_put_minor(&dev->render);

err_g11:

	if (drm_core_check_feature(dev, DRIVER_MODESET))

		drm_put_minor(&dev->control);

err_g1: