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>
Signed-off-by: Thomas Hellstrom <thellstrom@vmware.com>

1 files changed, 8 insertions, 0 deletions

diff --git a/drmP.h b/drmP.h
index 79e4c97..152f533 100644
--- a/drmP.h
+++ b/drmP.h
@@ -161,6 +161,7 @@ extern void drm_ut_debug_printk(unsigned int request_level,
 #define DRIVER_IRQ_VBL2    0x800
 #define DRIVER_MODESET     0x2000
 #define DRIVER_PRIME       0x4000
+#define DRIVER_RENDER      0x8000
 
 /***********************************************************************/
 /** \name Begin the DRM... */
@@ -1123,6 +1124,7 @@ 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 */
 
 	/** \name Drawable information */
 	/*@{ */
@@ -1206,6 +1208,11 @@ static inline int drm_mtrr_del(int handle, unsigned long offset,
 }
 #endif
 
+static inline bool drm_is_render_client(struct drm_file *file_priv)
+{
+	return file_priv->minor->type == DRM_MINOR_RENDER;
+}
+
 /******************************************************************/
 /** \name Internal function definitions */
 /*@{*/
@@ -1433,6 +1440,7 @@ extern int drm_get_dev(struct pci_dev *pdev, const struct pci_device_id *ent,
 extern void drm_put_dev(struct drm_device *dev);
 extern int drm_put_minor(struct drm_minor **minor);
 extern unsigned int drm_debug;
+extern unsigned int drm_rnodes;
 
 extern unsigned int drm_vblank_offdelay;
 extern unsigned int drm_timestamp_precision;