Thank you Stefan,
In VMM, the virtual address spaces of VM is starting from the base address (_ram.base( ) ) to the size of RAM (256MB). Is that correct? my question is how do we read the contents of physical memory of VM inside VMM/secure world.
Thanks,
On Friday, December 12, 2014, Stefan Kalkowski < stefan.kalkowski@...1...> wrote:
Hi Joseph,
On 12/11/2014 02:54 AM, Joseph Lee wrote:
Thanks Stefan for your detailed explanation.
Is there something similar to the |/dev/mem| and system call |mmap()
technique to |access
physical memory region in guest VM RAM from VMM?
In Genode there is no global view regarding physical memory like "/dev/mem" in Linux. Corresponding to your system's policy you can gain a specific amount of anonymous RAM from the system, or specific I/O memory regions (e.g. for device drivers) referenced by their physical memory address. For the TrustZone scenario we added a fixed portion of RAM to the I/O memory regions administered by the core process. Thereby, the VMM is able to request the VM's RAM via an IOMEM session during its startup routine. Such memory is mapped as uncached to the VMM's address space. The VMM has to copy over at least the kernel to the VM's RAM before starting the non-secure guest OS.
To sum it up, you don't need to care about gaining the VM's physical memory nor about mapping it, as it is already present in the VMM's address space. But if you want to read/write from/to it, you have to assure that the guest OS will either not cache the memory region used for hypervisor communication, or the guest OS has to flush the related cache lines whenever it wrote to it, or invalidates them before reading it.
Regards Stefan
Thanks in advance for answers
Kind regards,
Joseph
On Mon, Nov 17, 2014 at 8:03 AM, Stefan Kalkowski <stefan.kalkowski@...1... javascript:; <mailto:stefan.kalkowski@...1... javascript:;>> wrote:
Hello Joseph, On 11/17/2014 04:04 AM, Joseph Lee wrote: > Hi > > From the article in this link > http://genode.org/documentation/articles/trustzone , I understoodthat
> the DDR RAM in i.mx53 QSB is partitioned off between normal worldand
> secure world. I just want to read a file in the normal world from > application running in the secure side. Is there any possibility to get > access to any file in normal world from the secure world? thanksfor
> your help in advance. > If you want to access files in the "secure world", you first needsome
interface in between, which is not existent right now, at least notfor
file access. When designing such an interface, e.g. by adding aspecial
file system driver in Linux that communicates via hypercalls with the "secure world", you can of course define a dedicated memory area ofthe
"normal world" to be used to transfer payload. Although the DDR RAM is partitioned between both worlds that doesn't mean the "secure world" can't access memory of the "normal world". It only means that the memory assigned to the "secure world" can be accessed exclusively by it, and not by the "normal world". Nevertheless, caution is advised when using shared memory in between both worlds, as long as the memory might land in the cache of eitherof
both worlds. The cache is TrustZone aware, and tags all cache linesto
be secure, or non-secure, thereby effectively partitioning the cache. So if you use shared memory in between "secure" and "normal world" it needs to be either marked as uncached, or you need to clean the corresponding cache-lines after writing data to shared memory respectively invalidate cache-lines before reading data from shared memory. I hope this clarifies your question? Regards Stefan > Regards, > Joseph > > >
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