drm: mark context support as a legacy subsystem

So after a lot of digging around in git histories it looks like this
has only ever be used by dri1 render clients. Hence we can fully
disable the entire thing for modesetting drivers and so greatly reduce
the attack surface for potential exploits (or at least tools like
trinity ...).

Also add the drm_legacy prefix for functions which are called from
common code. To further reduce the impact on common code also extract
all the ctx release handling into a function (instead of only
releasing individual handles) and make ctxbitmap_cleanup return void -
it can never fail.
Reviewed-by: Eric Anholt <eric@anholt.net>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Signed-off-by: Dave Airlie <airlied@redhat.com>

drivers/gpu/drm/drm_context.c

@@ -42,10 +42,6 @@
 
 #include <drm/drmP.h>
 
-/******************************************************************/
-/** \name Context bitmap support */
-/*@{*/
-
 /**
  * Free a handle from the context bitmap.
  *
@@ -56,13 +52,48 @@
  * in drm_device::ctx_idr, while holding the drm_device::struct_mutex
  * lock.
  */
-void drm_ctxbitmap_free(struct drm_device * dev, int ctx_handle)
+static void drm_ctxbitmap_free(struct drm_device * dev, int ctx_handle)
 {
+	if (drm_core_check_feature(dev, DRIVER_MODESET))
+		return;
+
 	mutex_lock(&dev->struct_mutex);
 	idr_remove(&dev->ctx_idr, ctx_handle);
 	mutex_unlock(&dev->struct_mutex);
 }
 
+/******************************************************************/
+/** \name Context bitmap support */
+/*@{*/
+
+void drm_legacy_ctxbitmap_release(struct drm_device *dev,
+				  struct drm_file *file_priv)
+{
+	if (drm_core_check_feature(dev, DRIVER_MODESET))
+		return;
+
+	mutex_lock(&dev->ctxlist_mutex);
+	if (!list_empty(&dev->ctxlist)) {
+		struct drm_ctx_list *pos, *n;
+
+		list_for_each_entry_safe(pos, n, &dev->ctxlist, head) {
+			if (pos->tag == file_priv &&
+			    pos->handle != DRM_KERNEL_CONTEXT) {
+				if (dev->driver->context_dtor)
+					dev->driver->context_dtor(dev,
+								  pos->handle);
+
+				drm_ctxbitmap_free(dev, pos->handle);
+
+				list_del(&pos->head);
+				kfree(pos);
+				--dev->ctx_count;
+			}
+		}
+	}
+	mutex_unlock(&dev->ctxlist_mutex);
+}
+
 /**
  * Context bitmap allocation.
  *
@@ -90,10 +121,12 @@ static int drm_ctxbitmap_next(struct drm_device * dev)
  *
  * Initialise the drm_device::ctx_idr
  */
-int drm_ctxbitmap_init(struct drm_device * dev)
+void drm_legacy_ctxbitmap_init(struct drm_device * dev)
 {
+	if (drm_core_check_feature(dev, DRIVER_MODESET))
+		return;
+
 	idr_init(&dev->ctx_idr);
-	return 0;
 }
 
 /**
@@ -104,7 +137,7 @@ int drm_ctxbitmap_init(struct drm_device * dev)
  * Free all idr members using drm_ctx_sarea_free helper function
  * while holding the drm_device::struct_mutex lock.
  */
-void drm_ctxbitmap_cleanup(struct drm_device * dev)
+void drm_legacy_ctxbitmap_cleanup(struct drm_device * dev)
 {
 	mutex_lock(&dev->struct_mutex);
 	idr_destroy(&dev->ctx_idr);
@@ -136,6 +169,9 @@ int drm_getsareactx(struct drm_device *dev, void *data,
 	struct drm_local_map *map;
 	struct drm_map_list *_entry;
 
+	if (drm_core_check_feature(dev, DRIVER_MODESET))
+		return -EINVAL;
+
 	mutex_lock(&dev->struct_mutex);
 
 	map = idr_find(&dev->ctx_idr, request->ctx_id);
@@ -180,6 +216,9 @@ int drm_setsareactx(struct drm_device *dev, void *data,
 	struct drm_local_map *map = NULL;
 	struct drm_map_list *r_list = NULL;
 
+	if (drm_core_check_feature(dev, DRIVER_MODESET))
+		return -EINVAL;
+
 	mutex_lock(&dev->struct_mutex);
 	list_for_each_entry(r_list, &dev->maplist, head) {
 		if (r_list->map
@@ -280,6 +319,9 @@ int drm_resctx(struct drm_device *dev, void *data,
 	struct drm_ctx ctx;
 	int i;
 
+	if (drm_core_check_feature(dev, DRIVER_MODESET))
+		return -EINVAL;
+
 	if (res->count >= DRM_RESERVED_CONTEXTS) {
 		memset(&ctx, 0, sizeof(ctx));
 		for (i = 0; i < DRM_RESERVED_CONTEXTS; i++) {
@@ -310,6 +352,9 @@ int drm_addctx(struct drm_device *dev, void *data,
 	struct drm_ctx_list *ctx_entry;
 	struct drm_ctx *ctx = data;
 
+	if (drm_core_check_feature(dev, DRIVER_MODESET))
+		return -EINVAL;
+
 	ctx->handle = drm_ctxbitmap_next(dev);
 	if (ctx->handle == DRM_KERNEL_CONTEXT) {
 		/* Skip kernel's context and get a new one. */
@@ -353,6 +398,9 @@ int drm_getctx(struct drm_device *dev, void *data, struct drm_file *file_priv)
 {
 	struct drm_ctx *ctx = data;
 
+	if (drm_core_check_feature(dev, DRIVER_MODESET))
+		return -EINVAL;
+
 	/* This is 0, because we don't handle any context flags */
 	ctx->flags = 0;
 
@@ -375,6 +423,9 @@ int drm_switchctx(struct drm_device *dev, void *data,
 {
 	struct drm_ctx *ctx = data;
 
+	if (drm_core_check_feature(dev, DRIVER_MODESET))
+		return -EINVAL;
+
 	DRM_DEBUG("%d\n", ctx->handle);
 	return drm_context_switch(dev, dev->last_context, ctx->handle);
 }
@@ -395,6 +446,9 @@ int drm_newctx(struct drm_device *dev, void *data,
 {
 	struct drm_ctx *ctx = data;
 
+	if (drm_core_check_feature(dev, DRIVER_MODESET))
+		return -EINVAL;
+
 	DRM_DEBUG("%d\n", ctx->handle);
 	drm_context_switch_complete(dev, file_priv, ctx->handle);
 
@@ -417,6 +471,9 @@ int drm_rmctx(struct drm_device *dev, void *data,
 {
 	struct drm_ctx *ctx = data;
 
+	if (drm_core_check_feature(dev, DRIVER_MODESET))
+		return -EINVAL;
+
 	DRM_DEBUG("%d\n", ctx->handle);
 	if (ctx->handle != DRM_KERNEL_CONTEXT) {
 		if (dev->driver->context_dtor)

drivers/gpu/drm/drm_fops.c

@@ -474,26 +474,7 @@ int drm_release(struct inode *inode, struct file *filp)
 	if (dev->driver->driver_features & DRIVER_GEM)
 		drm_gem_release(dev, file_priv);
 
-	mutex_lock(&dev->ctxlist_mutex);
-	if (!list_empty(&dev->ctxlist)) {
-		struct drm_ctx_list *pos, *n;
-
-		list_for_each_entry_safe(pos, n, &dev->ctxlist, head) {
-			if (pos->tag == file_priv &&
-			    pos->handle != DRM_KERNEL_CONTEXT) {
-				if (dev->driver->context_dtor)
-					dev->driver->context_dtor(dev,
-								  pos->handle);
-
-				drm_ctxbitmap_free(dev, pos->handle);
-
-				list_del(&pos->head);
-				kfree(pos);
-				--dev->ctx_count;
-			}
-		}
-	}
-	mutex_unlock(&dev->ctxlist_mutex);
+	drm_legacy_ctxbitmap_release(dev, file_priv);
 
 	mutex_lock(&dev->struct_mutex);
 

drivers/gpu/drm/drm_stub.c

@@ -288,13 +288,7 @@ int drm_fill_in_dev(struct drm_device *dev,
 			goto error_out_unreg;
 	}
 
-
-
-	retcode = drm_ctxbitmap_init(dev);
-	if (retcode) {
-		DRM_ERROR("Cannot allocate memory for context bitmap.\n");
-		goto error_out_unreg;
-	}
+	drm_legacy_ctxbitmap_init(dev);
 
 	if (driver->driver_features & DRIVER_GEM) {
 		retcode = drm_gem_init(dev);
@@ -463,7 +457,7 @@ void drm_put_dev(struct drm_device *dev)
 		drm_rmmap(dev, r_list->map);
 	drm_ht_remove(&dev->map_hash);
 
-	drm_ctxbitmap_cleanup(dev);
+	drm_legacy_ctxbitmap_cleanup(dev);
 
 	if (drm_core_check_feature(dev, DRIVER_MODESET))
 		drm_put_minor(&dev->control);

include/drm/drmP.h

@@ -1313,9 +1313,10 @@ extern int drm_newctx(struct drm_device *dev, void *data,
 extern int drm_rmctx(struct drm_device *dev, void *data,
 		     struct drm_file *file_priv);
 
-extern int drm_ctxbitmap_init(struct drm_device *dev);
-extern void drm_ctxbitmap_cleanup(struct drm_device *dev);
-extern void drm_ctxbitmap_free(struct drm_device *dev, int ctx_handle);
+extern void drm_legacy_ctxbitmap_init(struct drm_device *dev);
+extern void drm_legacy_ctxbitmap_cleanup(struct drm_device *dev);
+extern void drm_legacy_ctxbitmap_release(struct drm_device *dev,
+					 struct drm_file *file_priv);
 
 extern int drm_setsareactx(struct drm_device *dev, void *data,
 			   struct drm_file *file_priv);