Re: [PATCH 5/9] dma-buf: heaps: mtk_sec_heap: Initialise tee session

[Benjamin Gaignard]

Le 27/09/2023 à 20:56, Jeffrey Kardatzke a écrit :
> On Wed, Sep 27, 2023 at 8:18 AM Benjamin Gaignard
> <benjamin.gaignard@xxxxxxxxxxxxx> wrote:
> > Le 27/09/2023 à 15:46, Joakim Bech a écrit :
> > > On Mon, Sep 25, 2023 at 12:49:50PM +0000, Yong Wu (吴勇) wrote:
> > > > On Tue, 2023-09-12 at 11:32 +0200, AngeloGioacchino Del Regno wrote:
> > > > > Il 12/09/23 08:17, Yong Wu (吴勇) ha scritto:
> > > > > > On Mon, 2023-09-11 at 11:29 +0200, AngeloGioacchino Del Regno
> > > > > > wrote:
> > > > > > > Il 11/09/23 04:30, Yong Wu ha scritto:
> > > > > > > > The TEE probe later than dma-buf heap, and PROBE_DEDER doesn't
> > > > > > > > work
> > > > > > > > here since this is not a platform driver, therefore initialise
> > > > > > > > the
> > > > > > > > TEE
> > > > > > > > context/session while we allocate the first secure buffer.
> > > > > > > >
> > > > > > > > Signed-off-by: Yong Wu <yong.wu@xxxxxxxxxxxx>
> > > > > > > > ---
> > > > > > > >      drivers/dma-buf/heaps/mtk_secure_heap.c | 61
> > > > > > > > +++++++++++++++++++++++++
> > > > > > > >      1 file changed, 61 insertions(+)
> > > > > > > >
> > > > > > > > diff --git a/drivers/dma-buf/heaps/mtk_secure_heap.c
> > > > > > > > b/drivers/dma-
> > > > > > > > buf/heaps/mtk_secure_heap.c
> > > > > > > > index bbf1c8dce23e..e3da33a3d083 100644
> > > > > > > > --- a/drivers/dma-buf/heaps/mtk_secure_heap.c
> > > > > > > > +++ b/drivers/dma-buf/heaps/mtk_secure_heap.c
> > > > > > > > @@ -10,6 +10,12 @@
> > > > > > > >      #include <linux/err.h>
> > > > > > > >      #include <linux/module.h>
> > > > > > > >      #include <linux/slab.h>
> > > > > > > > +#include <linux/tee_drv.h>
> > > > > > > > +#include <linux/uuid.h>
> > > > > > > > +
> > > > > > > > +#define TZ_TA_MEM_UUID          "4477588a-8476-11e2-ad15-
> > > > > > > > e41f1390d676"
> > > > > > > > +
> > > > > > > Is this UUID the same for all SoCs and all TZ versions?
> > > > > > Yes. It is the same for all SoCs and all TZ versions currently.
> > > > > That's good news!
> > > > >
> > > > > Is this UUID used in any userspace component? (example: Android
> > > > > HALs?)
> > > > No. Userspace never use it. If userspace would like to allocate this
> > > > secure buffer, it can achieve through the existing dmabuf IOCTL via
> > > > /dev/dma_heap/mtk_svp node.
> > > In general I think as mentioned elsewhere in comments, that there isn't
> > > that much here that seems to be unique for MediaTek in this patch
> > > series, so I think it worth to see whether this whole patch set can be
> > > made more generic. Having said that, the UUID is always unique for a
> > > certain Trusted Application. So, it's not entirely true saying that the
> > > UUID is the same for all SoCs and all TrustZone versions. It might be
> > > true for a family of MediaTek devices and the TEE in use, but not
> > > generically.
> > >
> > > So, if we need to differentiate between different TA implementations,
> > > then we need different UUIDs. If it would be possible to make this patch
> > > set generic, then it sounds like a single UUID would be sufficient, but
> > > that would imply that all TA's supporting such a generic UUID would be
> > > implemented the same from an API point of view. Which also means that
> > > for example Trusted Application function ID's needs to be the same etc.
> > > Not impossible to achieve, but still not easy (different TEE follows
> > > different specifications) and it's not typically something we've done in
> > > the past.
> > >
> > > Unfortunately there is no standardized database of TA's describing what
> > > they implement and support.
> > >
> > > As an alternative, we could implement a query call in the TEE answering,
> > > "What UUID does your TA have that implements secure unmapped heap?".
> > > I.e., something that reminds of a lookup table. Then we wouldn't have to
> > > carry this in UAPI, DT or anywhere else.
> > Joakim does a TA could offer a generic API and hide the hardware specific
> > details (like kernel uAPI does for drivers) ?
> It would have to go through another layer (like the tee driver) to be
> a generic API. The main issue with TAs is that they have UUIDs you
> need to connect to and specific codes for each function; so we should
> abstract at a layer above where those exist in the dma-heap code.
> > Aside that question I wonder what are the needs to perform a 'secure' playback.
> > I have in mind 2 requirements:
> > - secure memory regions, which means configure the hardware to ensure that only
> > dedicated hardware blocks and read or write into it.
> > - set hardware blocks in secure modes so they access to secure memory.
> > Do you see something else ?
> This is more or less what is required, but this is out of scope for
> the Linux kernel since it can't be trusted to do these things...this
> is all done in firmware or the TEE itself.

Yes kernel can't be trusted to do these things but know what we need could help
to define a API for a generic TA.

Just to brainstorm on mailing list:
What about a TA API like
TA_secure_memory_region() and TA_unsecure_memory_region() with parameters like:
- device identifier (an ID or compatible string maybe)
- memory region (physical address, size, offset)
- requested access rights (read, write)

and on kernel side a IOMMU driver because it basically have all this information already
(device attachment, kernel map/unmap).

In my mind it sound like a solution to limit the impact (new controls, new memory type)
inside v4l2. Probably we won't need new heap either.
All hardware dedicated implementations could live inside the TA which can offer a generic
API.

> > Regards,
> > Benjamin