drm/msm: protect against faults from copy_from_user() in submit ioctl

commit d78d383a upstream.

An evil userspace could try to cause deadlock by passing an unfaulted-in
GEM bo as submit->bos (or submit->cmds) table.  Which will trigger
msm_gem_fault() while we already hold struct_mutex.  See:

https://github.com/freedreno/msmtest/blob/master/evilsubmittest.cSigned-off-by: Rob Clark <robdclark@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/gpu/drm/msm/msm_drv.h

@@ -148,6 +148,12 @@ struct msm_drm_private {
 	} vram;
 
 	struct msm_vblank_ctrl vblank_ctrl;
+
+	/* task holding struct_mutex.. currently only used in submit path
+	 * to detect and reject faults from copy_from_user() for submit
+	 * ioctl.
+	 */
+	struct task_struct *struct_mutex_task;
 };
 
 struct msm_format {

drivers/gpu/drm/msm/msm_gem.c

@@ -196,11 +196,20 @@ int msm_gem_fault(struct vm_area_struct *vma, struct vm_fault *vmf)
 {
 	struct drm_gem_object *obj = vma->vm_private_data;
 	struct drm_device *dev = obj->dev;
+	struct msm_drm_private *priv = dev->dev_private;
 	struct page **pages;
 	unsigned long pfn;
 	pgoff_t pgoff;
 	int ret;
 
+	/* This should only happen if userspace tries to pass a mmap'd
+	 * but unfaulted gem bo vaddr into submit ioctl, triggering
+	 * a page fault while struct_mutex is already held.  This is
+	 * not a valid use-case so just bail.
+	 */
+	if (priv->struct_mutex_task == current)
+		return VM_FAULT_SIGBUS;
+
 	/* Make sure we don't parallel update on a fault, nor move or remove
 	 * something from beneath our feet
 	 */

drivers/gpu/drm/msm/msm_gem_submit.c

@@ -394,6 +394,7 @@ int msm_ioctl_gem_submit(struct drm_device *dev, void *data,
 		return -ENOMEM;
 
 	mutex_lock(&dev->struct_mutex);
+	priv->struct_mutex_task = current;
 
 	ret = submit_lookup_objects(submit, args, file);
 	if (ret)
@@ -479,6 +480,7 @@ int msm_ioctl_gem_submit(struct drm_device *dev, void *data,
 	submit_cleanup(submit);
 	if (ret)
 		msm_gem_submit_free(submit);
+	priv->struct_mutex_task = NULL;
 	mutex_unlock(&dev->struct_mutex);
 	return ret;
 }