Re: [PATCH v4 4/7] dma-buf: heaps: restricted_heap: Add dma_ops

["Yong Wu (吴勇)" <Yong.Wu@mediatek.com>]

On Fri, 2024-01-12 at 10:49 +0100, Daniel Vetter wrote:
>  	 
> External email : Please do not click links or open attachments until
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>  On Fri, Jan 12, 2024 at 10:41:14AM +0100, Daniel Vetter wrote:
> > On Fri, Jan 12, 2024 at 05:20:11PM +0800, Yong Wu wrote:
> > > Add the dma_ops for this restricted heap. For restricted buffer,
> > > cache_ops/mmap are not allowed, thus return EPERM for them.
> > > 
> > > Signed-off-by: Yong Wu <yong.wu@mediatek.com>
> > > ---
> > >  drivers/dma-buf/heaps/restricted_heap.c | 103
> ++++++++++++++++++++++++
> > >  1 file changed, 103 insertions(+)
> > > 
> > > diff --git a/drivers/dma-buf/heaps/restricted_heap.c
> b/drivers/dma-buf/heaps/restricted_heap.c
> > > index 8c266a0f6192..ec4c63d2112d 100644
> > > --- a/drivers/dma-buf/heaps/restricted_heap.c
> > > +++ b/drivers/dma-buf/heaps/restricted_heap.c
> > > @@ -12,6 +12,10 @@
> > >  
> > >  #include "restricted_heap.h"
> > >  
> > > +struct restricted_heap_attachment {
> > > +struct sg_table*table;
> > > +};
> > > +
> > >  static int
> > >  restricted_heap_memory_allocate(struct restricted_heap *heap,
> struct restricted_buffer *buf)
> > >  {
> > > @@ -45,6 +49,104 @@ restricted_heap_memory_free(struct
> restricted_heap *heap, struct restricted_buff
> > >  ops->memory_free(heap, buf);
> > >  }
> > >  
> > > +static int restricted_heap_attach(struct dma_buf *dmabuf, struct
> dma_buf_attachment *attachment)
> > > +{
> > > +struct restricted_buffer *restricted_buf = dmabuf->priv;
> > > +struct restricted_heap_attachment *a;
> > > +struct sg_table *table;
> > > +int ret;
> > > +
> > > +a = kzalloc(sizeof(*a), GFP_KERNEL);
> > > +if (!a)
> > > +return -ENOMEM;
> > > +
> > > +table = kzalloc(sizeof(*table), GFP_KERNEL);
> > > +if (!table) {
> > > +ret = -ENOMEM;
> > > +goto err_free_attach;
> > > +}
> > > +
> > > +ret = sg_alloc_table(table, 1, GFP_KERNEL);
> > > +if (ret)
> > > +goto err_free_sgt;
> > > +sg_set_page(table->sgl, NULL, restricted_buf->size, 0);
> > 
> > So this is definitely broken and violating the dma-buf api rules.
> You
> > cannot let attach succed and supply a dummy/invalid sg table.
> > 
> > Two options:
> > 
> > - Reject ->attach for all this buffers with -EBUSY and provide
> instead a
> >   private api for these secure buffers, similar to how
> virtio_dma_buf has
> >   private virto-specific apis. This interface would need to be
> >   standardized across all arm TEE users, so that we don't have a
> >   disastrous proliferation of apis.
> > 
> > - Allow ->attach, but _only_ for drivers/devices which can access
> the
> >   secure buffer correctly, and only if you can put the right secure
> buffer
> >   address into the sg table directly. If dma to a secure buffer for
> a
> >   given struct device * will not work correctly (i.e. without data
> >   corruption), you _must_ reject the attach attempt with -EBUSY.
> > 
> > The 2nd approach would be my preferred one, if it's technically
> possible.
> > 
> > Also my understanding is that arm TEE is standardized, so I think
> we'll at
> > least want some acks from other soc people whether this will work
> for them
> > too.
> > 
> > Finally the usual drill:
> > - this also needs the driver side support, if there's any changes
> needed.
> >   Just the new heap isn't enough.
> 
> Ok I quickly scrolled through your drm patches and that confirms that
> the
> current dma-buf interface you're implementing is just completely
> breaking
> the api. And you need to paper over that will all kinds of very icky
> special-casing.
> 
> So definitely need to rethink the overall design between dma-buf
> heaps and
> drivers here.

Hi,

Thanks very much for the review, and sorry for reply so late.  We
reconstructed our TEE commands so that the kernel can obtain the valid
PA/pages, then the sg operations can run normally. 

I will send the next version.
Thanks.

> -Sima
> 
> > - and for drm you need open userspace for this. Doesn't have to be
> the
> >   full content protection decode pipeline, the drivers in drm that
> landed
> >   secure buffer support thus far enabled it using the
> >   EGL_EXT_protected_content extension using gl, which side steps
> all the
> >   complications around content decryption keys and support
> > 
> > Cheers, Sima
> > 
> > > +
> > > +a->table = table;
> > > +attachment->priv = a;
> > > +
> > > +return 0;
> > > +
> > > +err_free_sgt:
> > > +kfree(table);
> > > +err_free_attach:
> > > +kfree(a);
> > > +return ret;
> > > +}
> > > +
> > > +static void restricted_heap_detach(struct dma_buf *dmabuf,
> struct dma_buf_attachment *attachment)
> > > +{
> > > +struct restricted_heap_attachment *a = attachment->priv;
> > > +
> > > +sg_free_table(a->table);
> > > +kfree(a->table);
> > > +kfree(a);
> > > +}
> > > +
> > > +static struct sg_table *
> > > +restricted_heap_map_dma_buf(struct dma_buf_attachment
> *attachment, enum dma_data_direction direct)
> > > +{
> > > +struct restricted_heap_attachment *a = attachment->priv;
> > > +struct sg_table *table = a->table;
> > > +
> > > +return table;
> > > +}
> > > +
> > > +static void
> > > +restricted_heap_unmap_dma_buf(struct dma_buf_attachment
> *attachment, struct sg_table *table,
> > > +      enum dma_data_direction direction)
> > > +{
> > > +struct restricted_heap_attachment *a = attachment->priv;
> > > +
> > > +WARN_ON(a->table != table);
> > > +}
> > > +
> > > +static int
> > > +restricted_heap_dma_buf_begin_cpu_access(struct dma_buf *dmabuf,
> enum dma_data_direction direction)
> > > +{
> > > +return -EPERM;
> > > +}
> > > +
> > > +static int
> > > +restricted_heap_dma_buf_end_cpu_access(struct dma_buf *dmabuf,
> enum dma_data_direction direction)
> > > +{
> > > +return -EPERM;
> > > +}
> > > +
> > > +static int restricted_heap_dma_buf_mmap(struct dma_buf *dmabuf,
> struct vm_area_struct *vma)
> > > +{
> > > +return -EPERM;
> > > +}
> > > +
> > > +static void restricted_heap_free(struct dma_buf *dmabuf)
> > > +{
> > > +struct restricted_buffer *restricted_buf = dmabuf->priv;
> > > +struct restricted_heap *heap =
> dma_heap_get_drvdata(restricted_buf->heap);
> > > +
> > > +restricted_heap_memory_free(heap, restricted_buf);
> > > +kfree(restricted_buf);
> > > +}
> > > +
> > > +static const struct dma_buf_ops restricted_heap_buf_ops = {
> > > +.attach= restricted_heap_attach,
> > > +.detach= restricted_heap_detach,
> > > +.map_dma_buf= restricted_heap_map_dma_buf,
> > > +.unmap_dma_buf= restricted_heap_unmap_dma_buf,
> > > +.begin_cpu_access = restricted_heap_dma_buf_begin_cpu_access,
> > > +.end_cpu_access= restricted_heap_dma_buf_end_cpu_access,
> > > +.mmap= restricted_heap_dma_buf_mmap,
> > > +.release= restricted_heap_free,
> > > +};
> > > +
> > >  static struct dma_buf *
> > >  restricted_heap_allocate(struct dma_heap *heap, unsigned long
> size,
> > >   unsigned long fd_flags, unsigned long heap_flags)
> > > @@ -66,6 +168,7 @@ restricted_heap_allocate(struct dma_heap
> *heap, unsigned long size,
> > >  if (ret)
> > >  goto err_free_buf;
> > >  exp_info.exp_name = dma_heap_get_name(heap);
> > > +exp_info.ops = &restricted_heap_buf_ops;
> > >  exp_info.size = restricted_buf->size;
> > >  exp_info.flags = fd_flags;
> > >  exp_info.priv = restricted_buf;
> > > -- 
> > > 2.25.1
> > > 
> > 
> > -- 
> > Daniel Vetter
> > Software Engineer, Intel Corporation
> > http://blog.ffwll.ch
>