drm: Turn off Legacy Context Functions

The context functions are not used by the i915 driver and should not
be used by modeset drivers. These driver functions contain several bugs
and security holes. This change makes these functions optional can be
turned on by a setting, they are turned off by default for modeset
driver with the exception of the nouvea driver that may require them with
an old version of libdrm.

The previous attempt was

commit 7c510133d9
Author: Daniel Vetter <daniel.vetter@ffwll.ch>
Date:   Thu Aug 8 15:41:21 2013 +0200

    drm: mark context support as a legacy subsystem

but this had to be reverted

commit c21eb21cb5
Author: Dave Airlie <airlied@redhat.com>
Date:   Fri Sep 20 08:32:59 2013 +1000

    Revert "drm: mark context support as a legacy subsystem"

v2: remove returns from void function, and formatting (Daniel Vetter)

v3:
- s/Nova/nouveau/ in the commit message, and add references to the
  previous attempts
- drop the part touching the drm hw lock, that should be a separate
  patch.

Signed-off-by: Peter Antoine <peter.antoine@intel.com> (v2)
Cc: Peter Antoine <peter.antoine@intel.com> (v2)
Reviewed-by: Peter Antoine <peter.antoine@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/drm_context.c

@@ -53,6 +53,10 @@ struct drm_ctx_list {
  */
 void drm_legacy_ctxbitmap_free(struct drm_device * dev, int ctx_handle)
 {
+	if (!drm_core_check_feature(dev, DRIVER_KMS_LEGACY_CONTEXT) &&
+	    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);
@@ -87,6 +91,10 @@ static int drm_legacy_ctxbitmap_next(struct drm_device * dev)
  */
 int drm_legacy_ctxbitmap_init(struct drm_device * dev)
 {
+	if (!drm_core_check_feature(dev, DRIVER_KMS_LEGACY_CONTEXT) &&
+	    drm_core_check_feature(dev, DRIVER_MODESET))
+		return -EINVAL;
+
 	idr_init(&dev->ctx_idr);
 	return 0;
 }
@@ -101,6 +109,10 @@ int drm_legacy_ctxbitmap_init(struct drm_device * dev)
  */
 void drm_legacy_ctxbitmap_cleanup(struct drm_device * dev)
 {
+	if (!drm_core_check_feature(dev, DRIVER_KMS_LEGACY_CONTEXT) &&
+	    drm_core_check_feature(dev, DRIVER_MODESET))
+		return;
+
 	mutex_lock(&dev->struct_mutex);
 	idr_destroy(&dev->ctx_idr);
 	mutex_unlock(&dev->struct_mutex);
@@ -119,6 +131,10 @@ void drm_legacy_ctxbitmap_flush(struct drm_device *dev, struct drm_file *file)
 {
 	struct drm_ctx_list *pos, *tmp;
 
+	if (!drm_core_check_feature(dev, DRIVER_KMS_LEGACY_CONTEXT) &&
+	    drm_core_check_feature(dev, DRIVER_MODESET))
+		return;
+
 	mutex_lock(&dev->ctxlist_mutex);
 
 	list_for_each_entry_safe(pos, tmp, &dev->ctxlist, head) {
@@ -161,6 +177,10 @@ int drm_legacy_getsareactx(struct drm_device *dev, void *data,
 	struct drm_local_map *map;
 	struct drm_map_list *_entry;
 
+	if (!drm_core_check_feature(dev, DRIVER_KMS_LEGACY_CONTEXT) &&
+	    drm_core_check_feature(dev, DRIVER_MODESET))
+		return -EINVAL;
+
 	mutex_lock(&dev->struct_mutex);
 
 	map = idr_find(&dev->ctx_idr, request->ctx_id);
@@ -205,6 +225,10 @@ int drm_legacy_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_KMS_LEGACY_CONTEXT) &&
+	    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
@@ -305,6 +329,10 @@ int drm_legacy_resctx(struct drm_device *dev, void *data,
 	struct drm_ctx ctx;
 	int i;
 
+	if (!drm_core_check_feature(dev, DRIVER_KMS_LEGACY_CONTEXT) &&
+	    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++) {
@@ -335,6 +363,10 @@ int drm_legacy_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_KMS_LEGACY_CONTEXT) &&
+	    drm_core_check_feature(dev, DRIVER_MODESET))
+		return -EINVAL;
+
 	ctx->handle = drm_legacy_ctxbitmap_next(dev);
 	if (ctx->handle == DRM_KERNEL_CONTEXT) {
 		/* Skip kernel's context and get a new one. */
@@ -378,6 +410,10 @@ int drm_legacy_getctx(struct drm_device *dev, void *data,
 {
 	struct drm_ctx *ctx = data;
 
+	if (!drm_core_check_feature(dev, DRIVER_KMS_LEGACY_CONTEXT) &&
+	    drm_core_check_feature(dev, DRIVER_MODESET))
+		return -EINVAL;
+
 	/* This is 0, because we don't handle any context flags */
 	ctx->flags = 0;
 
@@ -400,6 +436,10 @@ int drm_legacy_switchctx(struct drm_device *dev, void *data,
 {
 	struct drm_ctx *ctx = data;
 
+	if (!drm_core_check_feature(dev, DRIVER_KMS_LEGACY_CONTEXT) &&
+	    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);
 }
@@ -420,6 +460,10 @@ int drm_legacy_newctx(struct drm_device *dev, void *data,
 {
 	struct drm_ctx *ctx = data;
 
+	if (!drm_core_check_feature(dev, DRIVER_KMS_LEGACY_CONTEXT) &&
+	    drm_core_check_feature(dev, DRIVER_MODESET))
+		return -EINVAL;
+
 	DRM_DEBUG("%d\n", ctx->handle);
 	drm_context_switch_complete(dev, file_priv, ctx->handle);
 
@@ -442,6 +486,10 @@ int drm_legacy_rmctx(struct drm_device *dev, void *data,
 {
 	struct drm_ctx *ctx = data;
 
+	if (!drm_core_check_feature(dev, DRIVER_KMS_LEGACY_CONTEXT) &&
+	    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_drv.c

@@ -582,9 +582,12 @@ struct drm_device *drm_dev_alloc(struct drm_driver *driver,
 	if (drm_ht_create(&dev->map_hash, 12))
 		goto err_minors;
 
+	if (drm_core_check_feature(dev, DRIVER_KMS_LEGACY_CONTEXT) ||
+		!drm_core_check_feature(dev, DRIVER_MODESET))
 		ret = drm_legacy_ctxbitmap_init(dev);
 		if (ret) {
-		DRM_ERROR("Cannot allocate memory for context bitmap.\n");
+			DRM_ERROR(
+				"Cannot allocate memory for context bitmap.\n");
 			goto err_ht;
 		}
 

drivers/gpu/drm/nouveau/nouveau_drm.c

@@ -941,7 +941,8 @@ static struct drm_driver
 driver_stub = {
 	.driver_features =
 		DRIVER_USE_AGP |
-		DRIVER_GEM | DRIVER_MODESET | DRIVER_PRIME | DRIVER_RENDER,
+		DRIVER_GEM | DRIVER_MODESET | DRIVER_PRIME | DRIVER_RENDER |
+		DRIVER_KMS_LEGACY_CONTEXT,
 
 	.load = nouveau_drm_load,
 	.unload = nouveau_drm_unload,

include/drm/drmP.h

@@ -148,6 +148,7 @@ void drm_err(const char *format, ...);
 #define DRIVER_PRIME			0x4000
 #define DRIVER_RENDER			0x8000
 #define DRIVER_ATOMIC			0x10000
+#define DRIVER_KMS_LEGACY_CONTEXT	0x20000
 
 /***********************************************************************/
 /** \name Macros to make printk easier */