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: David Herrmann <dh.herrmann@gmail.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>

6 files changed, 51 insertions, 13 deletions

diff --git a/drivers/gpu/drm/drm_drv.c b/drivers/gpu/drm/drm_drv.c
index 288da3dc2a09..e572dd20bdee 100644
--- a/drivers/gpu/drm/drm_drv.c
+++ b/drivers/gpu/drm/drm_drv.c
@@ -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)) {
diff --git a/drivers/gpu/drm/drm_fops.c b/drivers/gpu/drm/drm_fops.c
index 136c949307ba..4be8e09a32ef 100644
--- a/drivers/gpu/drm/drm_fops.c
+++ b/drivers/gpu/drm/drm_fops.c
@@ -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);
@@ -478,7 +477,8 @@ 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 */
-	drm_master_put(&file_priv->master);
+	if (file_priv->master)
+		drm_master_put(&file_priv->master);
 	file_priv->is_master = 0;
 	list_del(&file_priv->lhead);
 	mutex_unlock(&dev->struct_mutex);
diff --git a/drivers/gpu/drm/drm_pci.c b/drivers/gpu/drm/drm_pci.c
index 3fca2db1c40c..1f96cee6eee8 100644
--- a/drivers/gpu/drm/drm_pci.c
+++ b/drivers/gpu/drm/drm_pci.c
@@ -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:
diff --git a/drivers/gpu/drm/drm_platform.c b/drivers/gpu/drm/drm_platform.c
index 400024b6d512..f7a18c6ba4c4 100644
--- a/drivers/gpu/drm/drm_platform.c
+++ b/drivers/gpu/drm/drm_platform.c
@@ -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:
diff --git a/drivers/gpu/drm/drm_stub.c b/drivers/gpu/drm/drm_stub.c
index e30bb0d7c67a..e7eb0276f7f1 100644
--- a/drivers/gpu/drm/drm_stub.c
+++ b/drivers/gpu/drm/drm_stub.c
@@ -40,6 +40,9 @@
 unsigned int drm_debug = 0;	/* 1 to enable debug output */
 EXPORT_SYMBOL(drm_debug);
 
+unsigned int drm_rnodes = 0;	/* 1 to enable experimental render nodes API */
+EXPORT_SYMBOL(drm_rnodes);
+
 unsigned int drm_vblank_offdelay = 5000;    /* Default to 5000 msecs. */
 EXPORT_SYMBOL(drm_vblank_offdelay);
 
@@ -56,11 +59,13 @@ MODULE_AUTHOR(CORE_AUTHOR);
 MODULE_DESCRIPTION(CORE_DESC);
 MODULE_LICENSE("GPL and additional rights");
 MODULE_PARM_DESC(debug, "Enable debug output");
+MODULE_PARM_DESC(rnodes, "Enable experimental render nodes API");
 MODULE_PARM_DESC(vblankoffdelay, "Delay until vblank irq auto-disable [msecs]");
 MODULE_PARM_DESC(timestamp_precision_usec, "Max. error on timestamps [usecs]");
 MODULE_PARM_DESC(timestamp_monotonic, "Use monotonic timestamps");
 
 module_param_named(debug, drm_debug, int, 0600);
+module_param_named(rnodes, drm_rnodes, int, 0600);
 module_param_named(vblankoffdelay, drm_vblank_offdelay, int, 0600);
 module_param_named(timestamp_precision_usec, drm_timestamp_precision, int, 0600);
 module_param_named(timestamp_monotonic, drm_timestamp_monotonic, int, 0600);
@@ -446,6 +451,9 @@ void drm_put_dev(struct drm_device *dev)
 	if (drm_core_check_feature(dev, DRIVER_MODESET))
 		drm_put_minor(&dev->control);
 
+	if (dev->render)
+		drm_put_minor(&dev->render);
+
 	if (driver->driver_features & DRIVER_GEM)
 		drm_gem_destroy(dev);
 
@@ -462,6 +470,8 @@ void drm_unplug_dev(struct drm_device *dev)
 	/* for a USB device */
 	if (drm_core_check_feature(dev, DRIVER_MODESET))
 		drm_unplug_minor(dev->control);
+	if (dev->render)
+		drm_unplug_minor(dev->render);
 	drm_unplug_minor(dev->primary);
 
 	mutex_lock(&drm_global_mutex);
diff --git a/drivers/gpu/drm/drm_usb.c b/drivers/gpu/drm/drm_usb.c
index 34a156f0c336..87664723b9ce 100644
--- a/drivers/gpu/drm/drm_usb.c
+++ b/drivers/gpu/drm/drm_usb.c
@@ -33,6 +33,12 @@ int drm_get_usb_dev(struct usb_interface *interface,
 	if (ret)
 		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;
@@ -62,6 +68,9 @@ int drm_get_usb_dev(struct usb_interface *interface,
 err_g3:
 	drm_put_minor(&dev->primary);
 err_g2:
+	if (dev->render)
+		drm_put_minor(&dev->render);
+err_g11:
 	drm_put_minor(&dev->control);
 err_g1:
 	kfree(dev);