Write to specific memory address

[Vincent Raes]

Hello,

Thanks for the advice, it helped a lot. I was indeed confused with the
virtual memory since I could
I have another question, this time involving the tz_vmm itself. In mmu.h
there is a function which should translate a virtual address of the normal
world to a physical address in the secure world.
However this function only returns 0 due to the ram.h throwing an invalid
address when he gets called on by mmu.h. Could this be because I'm using a
different kernel in the normal world/ different board so that mmu.h does
not translate the addresses correctly?

Best regards,
Vincent

2015-03-23 9:27 GMT+01:00 Stefan Kalkowski <stefan.kalkowski at ...1...
>:

> Hello Vincent,
>
> On 03/20/2015 11:40 AM, Vincent Raes wrote:
> > Hello,
> >
> > I am working with TrustZone using Genode and I am trying to pass data
> > from the secure world to the normal world and vice versa. The problem
> > lies with the fact that the normal world can only access a certain part
> > of the RAM memory the board has to offer so all the data I want to give
> > to the normal world has to be placed somewhere it can access. And I
> > can't seem to figure out how to place data at a specific address using
> > Genode.
> >
> > When I try to use pointers to the wanted memory location, the error "No
> > RM attachment" keeps popping up. This may very well be caused by the
> > fact I am using a pointer to a place that does not yet has a valid data
> > object in it. I believe the correct answer has something to do with the
> > use of dataspaces but am not sure how or what kind of dataspace I need
> > to use for random data I generate myself.
>
> To me it seems you first have to understand the difference between
> virtual memory and physical memory. When using memory addresses in a
> normal application (and even mostly in the kernel) you are dealing with
> virtual memory addresses that are translated in hardware via the MMU to
> physical memory addresses. If you target a memory region that does not
> relate to a valid translation entry in the translation table of the
> process, you will get a translation fault. That is what you see with the
> message "No RM attachment". In Genode the RM session is used to
> administrate the virtual memory address space of a process.
>
> In contrast to that: the bus system, and the memory controller are
> dealing with physical memory addresses, and probably the TrustZone
> component that splits the memory in normal and secure one too. If you
> say that the normal world can access only a specific portion of RAM, you
> speak about a physical address range.
>
> Your intuition was right: in Genode a portion of RAM is abstracted by a
> dataspace. In general a RAM dataspace is just an anonymous amount of
> RAM, where you do cannot determine its location in physical memory when
> allocating it. In contrast to a RAM dataspace, you can also use an IOMEM
> session to request a specific dataspace, normally used for memory-mapped
> I/O regions of devices. When allocating an IOMEM region of course you
> can and have to specify the actual physical location. So in your case,
> the only possibility to deposit data at a specific RAM location for the
> normal world is to open up an IOMEM session, and attach its dataspace to
> the RM session of your application.
>
> BTW: the same was done in our TrustZone example virtual machine monitor
> implmentation (repos/os/src/server/tz_vmm).
>
> Regards
> Stefan
>
> >
> > Thanks in advance for any advice.
> >
> > Best regards,
> > Vincent
> >
> >
> >
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> --
> Stefan Kalkowski
> Genode Labs
>
> http://www.genode-labs.com/ · http://genode.org/
>
>
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