[i.MX53 QSB] Inter-component Shared Memory

[Christian Helmuth]

Hello Tiago,

nice to hear that you follow the component approach.

On Mon, Jun 06, 2016 at 04:54:46PM +0100, Tiago Brito wrote:
> As said in previous posts I have a system call which is responsible for the
> SMC between the normal world and tz_vmm. I can successfully allocate memory
> in the normal world and access it in the secure world. Thus I can send
> images to the secure world (which is what I want). Then in the secure world
> I have a new component which uses the libpng port to process images.

This component runs in its own address space and, thereby, does not
share memory mappings with tz_vmm after its creation.

> TZ_VMM and the libpng component talk using the inter-component RPC. In
> order to access the image inside the libpng component I send Genode::addr_t
> in the RPC function call argument. This Genode::addr_t has the physicall
> address of the image which was loaded to memory from Linux.
> 
> I can verify that the addr_t variable has the correct value inside the
> libpng component, but when I try to access it this is the output:
> 
> [init -> tz_vmm] image addr: 816ac000
> [init -> tz_vmm] RPC call: png_sig_cmp
> [init -> libpng_server] image addr: 816ac000
> no RM attachment (faulter 27213c with IP 700101d4 attempts to read from
> address 816ac000)
> init -> libpng_server -> ep: unresolved pagefault at ip=700101d4
> sp=e01fee30 fault address=816ac000
> core -> pager_ep: cannot submit unknown signal context
> 
> Since this is a memory block which was allocated by Linux, and since I can
> manipulate it fine when inside tz_vmm, shouldn't I be able to manipulate
> this same memory region without problems?

As components use virtual memory (based on page tables) memory is
addressed by virtual addresses. I assume that you use some facility in
tz_vmm to calculate the virtual-memory mapping of 0x816ac000 and
access the PNG in your original implementation. Now, you separated
tz_vmm and your libpng_server into two components and, so, the memory
mappings of tz_vmm are not directly accessible in libpng_server.
Passing the physical address to libpng_server does not help as this
component will not be allowed to create a virtual memory mapping to
this portion of the RAM - it is exclusively accessible in tz_vmm.

I suggest you establish a shared-memory dataspace between
libpng_server and tz_vmm big enough to transfer the PNG images. tz_vmm
can then copy the PNG data from (Linux) guest memory into the shared
dataspace where it is accessible by libpng_server. For an example,
please have a look at Terminal::Session and the Genode Foundations
book Section 3.6.3. and 3.6.5.

Regards
-- 
Christian Helmuth
Genode Labs

http://www.genode-labs.com/ · http://genode.org/
https://twitter.com/GenodeLabs · /ˈdʒiː.nəʊd/

Genode Labs GmbH · Amtsgericht Dresden · HRB 28424 · Sitz Dresden
Geschäftsführer: Dr.-Ing. Norman Feske, Christian Helmuth