drm: Assert held reservation lock for dma-buf mmapping

When userspace mmaps dma-buf's fd, the dma-buf reservation lock must be
held. Add locking sanity checks to the dma-buf mmaping callbacks of DRM
drivers to ensure that the locking assumptions won't regress in future.

Suggested-by: Daniel Vetter <daniel@ffwll.ch>
Signed-off-by: Dmitry Osipenko <dmitry.osipenko@collabora.com>
Acked-by: Christian König <christian.koenig@amd.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20221110201349.351294-3-dmitry.osipenko@collabora.com

drivers/gpu/drm/drm_prime.c

@@ -781,6 +781,8 @@ int drm_gem_dmabuf_mmap(struct dma_buf *dma_buf, struct vm_area_struct *vma)
 	struct drm_gem_object *obj = dma_buf->priv;
 	struct drm_device *dev = obj->dev;
 
+	dma_resv_assert_held(dma_buf->resv);
+
 	if (!dev->driver->gem_prime_mmap)
 		return -ENOSYS;
 

drivers/gpu/drm/i915/gem/i915_gem_dmabuf.c

@@ -97,6 +97,8 @@ static int i915_gem_dmabuf_mmap(struct dma_buf *dma_buf, struct vm_area_struct *
 	struct drm_i915_private *i915 = to_i915(obj->base.dev);
 	int ret;
 
+	dma_resv_assert_held(dma_buf->resv);
+
 	if (obj->base.size < vma->vm_end - vma->vm_start)
 		return -EINVAL;
 

drivers/gpu/drm/omapdrm/omap_gem_dmabuf.c

@@ -66,6 +66,8 @@ static int omap_gem_dmabuf_mmap(struct dma_buf *buffer,
 	struct drm_gem_object *obj = buffer->priv;
 	int ret = 0;
 
+	dma_resv_assert_held(buffer->resv);
+
 	ret = drm_gem_mmap_obj(obj, omap_gem_mmap_size(obj), vma);
 	if (ret < 0)
 		return ret;

drivers/gpu/drm/tegra/gem.c

@@ -694,6 +694,8 @@ static int tegra_gem_prime_mmap(struct dma_buf *buf, struct vm_area_struct *vma)
 	struct drm_gem_object *gem = buf->priv;
 	int err;
 
+	dma_resv_assert_held(buf->resv);
+
 	err = drm_gem_mmap_obj(gem, gem->size, vma);
 	if (err < 0)
 		return err;