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>

1 files changed, 9 insertions, 0 deletions

diff --git a/include/drm/drmP.h b/include/drm/drmP.h
index 0e3d517..2907341 100644
--- a/include/drm/drmP.h
+++ b/include/drm/drmP.h
@@ -145,6 +145,7 @@ int drm_err(const char *func, const char *format, ...);
 #define DRIVER_GEM         0x1000
 #define DRIVER_MODESET     0x2000
 #define DRIVER_PRIME       0x4000
+#define DRIVER_RENDER      0x8000
 
 #define DRIVER_BUS_PCI 0x1
 #define DRIVER_BUS_PLATFORM 0x2
@@ -290,6 +291,7 @@ typedef int drm_ioctl_compat_t(struct file *filp, unsigned int cmd,
 #define DRM_ROOT_ONLY	0x4
 #define DRM_CONTROL_ALLOW 0x8
 #define DRM_UNLOCKED	0x10
+#define DRM_RENDER_ALLOW 0x20
 
 struct drm_ioctl_desc {
 	unsigned int cmd;
@@ -1204,6 +1206,7 @@ struct drm_device {
 	unsigned int agp_buffer_token;
 	struct drm_minor *control;		/**< Control node for card */
 	struct drm_minor *primary;		/**< render type primary screen head */
+	struct drm_minor *render;		/**< render node for card */
 
         struct drm_mode_config mode_config;	/**< Current mode config */
 
@@ -1251,6 +1254,11 @@ static inline bool drm_modeset_is_locked(struct drm_device *dev)
 	return mutex_is_locked(&dev->mode_config.mutex);
 }
 
+static inline bool drm_is_render_client(struct drm_file *file_priv)
+{
+	return file_priv->minor->type == DRM_MINOR_RENDER;
+}
+
 /******************************************************************/
 /** \name Internal function definitions */
 /*@{*/
@@ -1450,6 +1458,7 @@ extern void drm_put_dev(struct drm_device *dev);
 extern int drm_put_minor(struct drm_minor **minor);
 extern void drm_unplug_dev(struct drm_device *dev);
 extern unsigned int drm_debug;
+extern unsigned int drm_rnodes;
 
 extern unsigned int drm_vblank_offdelay;
 extern unsigned int drm_timestamp_precision;