[Linaro-mm-sig] Re: [PATCH v5 2/9] drm/mediatek: Add secure buffer control flow to mtk_drm_gem

On Wed, Apr 03, 2024 at 06:26:54PM +0800, Shawn Sung wrote:

From: "Jason-JH.Lin" jason-jh.lin@mediatek.com

Add secure buffer control flow to mtk_drm_gem.

When user space takes DRM_MTK_GEM_CREATE_ENCRYPTED flag and size to create a mtk_drm_gem object, mtk_drm_gem will find a matched size dma buffer from secure dma-heap and bind it to mtk_drm_gem object.

Signed-off-by: Jason-JH.Lin jason-jh.lin@mediatek.com Signed-off-by: Hsiao Chien Sung shawn.sung@mediatek.com

---

drivers/gpu/drm/mediatek/mtk_gem.c | 85 +++++++++++++++++++++++++++++- drivers/gpu/drm/mediatek/mtk_gem.h | 4 ++ 2 files changed, 88 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/mediatek/mtk_gem.c b/drivers/gpu/drm/mediatek/mtk_gem.c index e59e0727717b7..ec34d02c14377 100644 --- a/drivers/gpu/drm/mediatek/mtk_gem.c +++ b/drivers/gpu/drm/mediatek/mtk_gem.c @@ -4,6 +4,8 @@ */ #include <linux/dma-buf.h> +#include <linux/dma-heap.h> +#include <uapi/linux/dma-heap.h> #include <drm/mediatek_drm.h> #include <drm/drm.h> @@ -102,6 +104,81 @@ struct mtk_gem_obj *mtk_gem_create(struct drm_device *dev, return ERR_PTR(ret); } +struct mtk_gem_obj *mtk_gem_create_from_heap(struct drm_device *dev,

• 			     const char *heap, size_t size)
  

+{

• struct mtk_drm_private *priv = dev->dev_private;
• struct mtk_gem_obj *mtk_gem;
• struct drm_gem_object *obj;
• struct dma_heap *dma_heap;
• struct dma_buf *dma_buf;
• struct dma_buf_attachment *attach;
• struct sg_table *sgt;
• struct iosys_map map = {};
• int ret;
• mtk_gem = mtk_gem_init(dev, size);
• if (IS_ERR(mtk_gem))

• return ERR_CAST(mtk_gem);
  

• obj = &mtk_gem->base;
• dma_heap = dma_heap_find(heap);
• if (!dma_heap) {

• DRM_ERROR("heap find fail\n");
  

• goto err_gem_free;
  

• }
• dma_buf = dma_heap_buffer_alloc(dma_heap, size,

• 			O_RDWR | O_CLOEXEC, DMA_HEAP_VALID_HEAP_FLAGS);
  

• if (IS_ERR(dma_buf)) {

• DRM_ERROR("buffer alloc fail\n");
  

• dma_heap_put(dma_heap);
  

• goto err_gem_free;
  

• }
• dma_heap_put(dma_heap);
• attach = dma_buf_attach(dma_buf, priv->dma_dev);
• if (IS_ERR(attach)) {

• DRM_ERROR("attach fail, return\n");
  

• dma_buf_put(dma_buf);
  

• goto err_gem_free;
  

• }
• sgt = dma_buf_map_attachment(attach, DMA_BIDIRECTIONAL);
• if (IS_ERR(sgt)) {

• DRM_ERROR("map failed, detach and return\n");
  

• dma_buf_detach(dma_buf, attach);
  

• dma_buf_put(dma_buf);
  

• goto err_gem_free;
  

• }
• obj->import_attach = attach;
• mtk_gem->dma_addr = sg_dma_address(sgt->sgl);
• mtk_gem->sg = sgt;
• mtk_gem->size = dma_buf->size;
• if (!strcmp(heap, "mtk_svp") || !strcmp(heap, "mtk_svp_cma")) {

• /* secure buffer can not be mapped */
  

• mtk_gem->secure = true;
  

• } else {

• ret = dma_buf_vmap(dma_buf, &map);
  

• mtk_gem->kvaddr = map.vaddr;
  

• if (ret) {
  

• 	DRM_ERROR("map failed, ret=%d\n", ret);
  

• 	dma_buf_unmap_attachment(attach, sgt, DMA_BIDIRECTIONAL);
  

• 	dma_buf_detach(dma_buf, attach);
  

• 	dma_buf_put(dma_buf);
  

• 	mtk_gem->kvaddr = NULL;
  

• }
  

• }
• return mtk_gem;

+err_gem_free:

• drm_gem_object_release(obj);
• kfree(mtk_gem);
• return ERR_PTR(-ENOMEM);

+}

void mtk_gem_free_object(struct drm_gem_object *obj) { struct mtk_gem_obj *mtk_gem = to_mtk_gem_obj(obj); @@ -229,7 +306,9 @@ struct drm_gem_object *mtk_gem_prime_import_sg_table(struct drm_device *dev, if (IS_ERR(mtk_gem)) return ERR_CAST(mtk_gem);

• mtk_gem->secure = !sg_page(sg->sgl); mtk_gem->dma_addr = sg_dma_address(sg->sgl);
• mtk_gem->size = attach->dmabuf->size; mtk_gem->sg = sg;

return &mtk_gem->base; @@ -304,7 +383,11 @@ int mtk_gem_create_ioctl(struct drm_device *dev, void *data, struct drm_mtk_gem_create *args = data; int ret;

• mtk_gem = mtk_gem_create(dev, args->size, false);

• if (args->flags & DRM_MTK_GEM_CREATE_ENCRYPTED)

• mtk_gem = mtk_gem_create_from_heap(dev, "mtk_svp_cma", args->size);
  

That heap doesn't exist upstream either. Also, I'm wondering if it's the right solution there.

From what I can tell, you want to allow to create encrypted buffers from the TEE. Why do we need this as a DRM ioctl at all? A heap seems like the perfect solution to do so, and then you just have to import it into DRM.

I'm also not entirely sure that not having a SG list is enough to consider the buffer secure. Wouldn't a buffer allocated without a kernel mapping also be in that situation?

Maxime