Write to specific memory address

Vincent Raes raes.vincent at ...9...
Fri Apr 3 15:28:20 CEST 2015 

Hello,

I have been doing some more experimenting with the va_to_pa function and
the communication between normal and secure world.
I am currently running Genode in the normal world as well. In the normal
world I create a RAM dataspace which I then attach to the rm_session of the
application. I fill this dataspace with data and I pass the virtual address
to the secure world. The va_to_pa function returns an actual value in this
case so my problem there was that I had nothing in the page table. The
problem however is that this address seems incorrect. When I change data at
that physical address in the secure world, the normal world does not see
any change in the dataspace when it has control again.
At first I thought this might have something to do with the cache but I'm
adding the UNCACHED modifier in the declaration of my dataspace and the
problem persists.

After some extra testing with as big a dataspace I could manage, I checked
the memory for where it was located and I found the dataspace, with all the
data in it, at a random memory address. This leads me to believe that the
translation of the virtual address of the dataspace to a physical one is
simply wrong. I think the virtual address of the dataspace is a local
address for that rm_session and that this might cause this mistranslation.

Now my question is, is it possible to find the virtual address of a
dataspace or anything in which I can store data that will translate to the
correct physical address with the va_to_pa function?

Best regards,
Vincent

2015-03-30 8:45 GMT+02:00 Stefan Kalkowski <stefan.kalkowski at ...1...
>:

> Hi Vincent,
>
> On 03/27/2015 04:32 PM, Vincent Raes wrote:
> > 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?
>
> These small helper functions in mmu.h are used to decode register values
> of the normal world that potentially contain virtual addresses to
> physical ones. Thereby it is assumed the guest OS uses the short
> translation table format of the ARM v7 architecture. If a given address
> is not found in the page tables, or if the guest OS did not setup the
> page tables yet (MMU ist still off) you will get a zero as return value.
>
> Regards
> Stefan
>
> >
> > Best regards,
> > Vincent
> >
> > 2015-03-23 9:27 GMT+01:00 Stefan Kalkowski
> > <stefan.kalkowski at ...1...
> > <mailto: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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> Stefan Kalkowski
> Genode Labs
>
> http://www.genode-labs.com/ · http://genode.org/
>
>
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