Re: [PATCH v3 03/11] drm/mediatek: Add secure buffer control flow to mtk_drm_gem

[Jeffrey Kardatzke]

On Fri, Jan 12, 2024 at 5:13 AM Daniel Vetter <daniel@xxxxxxxx> wrote:
>
> On Sun, Dec 24, 2023 at 02:29:24AM +0800, Jason-JH.Lin wrote:
> > 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@xxxxxxxxxxxx>
>
> Apologies for jumping rather late, but last year was a mess here.
>
> There's the fundamental issue that this is new uapi, and it needs open
> userspace, and I haven't seen that.

The open userspace for it is currently in minigbm for ChromeOS here:
https://chromium.googlesource.com/chromiumos/platform/minigbm/+/main/mediatek.c#322

Does that satisfy that particular requirement?
>
> What's more, this is a pure kms api so there's no precedent at all for
> adding special ioctl to those - all the existing support for
> protected/restricted content buffers in upstream has used render nodes and
> EGL_EXT_protected_content in mesa3d to enable this feature on the drm/kms
> side. So I'm not exactly sure what your plan here is, but you need one,
> and it needs to be more than a testcase/demo.

I'm probably not understanding something here, but for the Intel
protected content allocation there was a specific structure
(drm_i915_gem_create_ext_protected_content) added to the
DRM_IOCTL_I915_GEM_CREATE_EXT ioctl in order to enable allocation of
protected buffers.  So wouldn't that be precedent for using an ioctl
like this to allocate a GEM object?

>
> The other issue, and the reason I've looked into the mtk code, is that the
> dma-buf implementation breaks the dma-buf api. So that needs to be
> changed.
Yeah, agreed here...I do see now that attaching dma_bufs for content
that is completely inaccessible by the kernel will be a no-go.
>
> Finally I think the primary way to display a protected content buffer on a
> pure kms driver should be by using prime fd2handle buffer importing.
> Because you're adding a dma-buf heap it's already possible for userspace
> to use this path (or at least try), and so we have to make this path work
> anyway.

Is what you're getting at here having MTK implement their own
gem_prime_import in order to work around having to do the dma_buf
attach operation? (from looking at the code, this appears to be the
only place in non-vendor specific code that dma_buf_attach is called)
>
> Once we have the prime import path working correctly for protected content
> buffers (which should shake out all the dma-api issues I've explained in
> the dma-buf heaps thread), it should be possible to implement the direct
> allocation function in a generic helper:
>
> struct drm_gem_object * drm_gem_create_object_from_heap(struct drm_device *dev,
>                                                         struct drm_file *file,
>                                                         struct drm_buf_heap *heap);
>
> Which does roughly:
>
> - allocate a dma-buf from the desired heap
> - import that dma-buf into the device using prime for the drm_file
> - using the already implemented driver import code for special cases like
>   protected content buffers
>
> There should be no need to hand-roll all this code here, and especially
> not have any special-casing for the heap string name or things like that.
> That all must be handled in the dma-buf prime import code.
>
> Cheers, Sima
>
> > ---
> >  drivers/gpu/drm/mediatek/mtk_drm_gem.c | 85 +++++++++++++++++++++++++-
> >  drivers/gpu/drm/mediatek/mtk_drm_gem.h |  4 ++
> >  2 files changed, 88 insertions(+), 1 deletion(-)
> >
> > diff --git a/drivers/gpu/drm/mediatek/mtk_drm_gem.c b/drivers/gpu/drm/mediatek/mtk_drm_gem.c
> > index 30e347adcbe9..858f34a735f8 100644
> > --- a/drivers/gpu/drm/mediatek/mtk_drm_gem.c
> > +++ b/drivers/gpu/drm/mediatek/mtk_drm_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>
> > @@ -55,6 +57,81 @@ static struct mtk_drm_gem_obj *mtk_drm_gem_init(struct drm_device *dev,
> >       return mtk_gem_obj;
> >  }
> >
> > +struct mtk_drm_gem_obj *mtk_drm_gem_create_from_heap(struct drm_device *dev,
> > +                                                  const char *heap, size_t size)
> > +{
> > +     struct mtk_drm_private *priv = dev->dev_private;
> > +     struct mtk_drm_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_drm_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);
> > +}
> > +
> >  struct mtk_drm_gem_obj *mtk_drm_gem_create(struct drm_device *dev,
> >                                          size_t size, bool alloc_kmap)
> >  {
> > @@ -225,7 +302,9 @@ 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;
> > @@ -301,7 +380,11 @@ int mtk_gem_create_ioctl(struct drm_device *dev, void *data,
> >       struct drm_mtk_gem_create *args = data;
> >       int ret;
> >
> > -     mtk_gem = mtk_drm_gem_create(dev, args->size, false);
> > +     if (args->flags & DRM_MTK_GEM_CREATE_ENCRYPTED)
> > +             mtk_gem = mtk_drm_gem_create_from_heap(dev, "mtk_svp_cma", args->size);
> > +     else
> > +             mtk_gem = mtk_drm_gem_create(dev, args->size, false);
> > +
> >       if (IS_ERR(mtk_gem))
> >               return PTR_ERR(mtk_gem);
> >
> > diff --git a/drivers/gpu/drm/mediatek/mtk_drm_gem.h b/drivers/gpu/drm/mediatek/mtk_drm_gem.h
> > index 90f3d2916ec5..8fd5ce827d4f 100644
> > --- a/drivers/gpu/drm/mediatek/mtk_drm_gem.h
> > +++ b/drivers/gpu/drm/mediatek/mtk_drm_gem.h
> > @@ -27,9 +27,11 @@ struct mtk_drm_gem_obj {
> >       void                    *cookie;
> >       void                    *kvaddr;
> >       dma_addr_t              dma_addr;
> > +     size_t                  size;
> >       unsigned long           dma_attrs;
> >       struct sg_table         *sg;
> >       struct page             **pages;
> > +     bool                    secure;
> >  };
> >
> >  #define to_mtk_gem_obj(x)    container_of(x, struct mtk_drm_gem_obj, base)
> > @@ -37,6 +39,8 @@ struct mtk_drm_gem_obj {
> >  void mtk_drm_gem_free_object(struct drm_gem_object *gem);
> >  struct mtk_drm_gem_obj *mtk_drm_gem_create(struct drm_device *dev, size_t size,
> >                                          bool alloc_kmap);
> > +struct mtk_drm_gem_obj *mtk_drm_gem_create_from_heap(struct drm_device *dev,
> > +                                                  const char *heap, size_t size);
> >  int mtk_drm_gem_dumb_create(struct drm_file *file_priv, struct drm_device *dev,
> >                           struct drm_mode_create_dumb *args);
> >  struct sg_table *mtk_gem_prime_get_sg_table(struct drm_gem_object *obj);
> > --
> > 2.18.0
> >
>
> --
> Daniel Vetter
> Software Engineer, Intel Corporation
> http://blog.ffwll.ch