Xen devel - May 2005 - RE: asterisk, ztdummy, and usb (and HZ = 100 under xen ???)

> Assuming you have restricted the domain to just accessing registers
and
> IRQs belonging to the device it controls, I think the only way would
be
> by programming the device to wreak havoc on its behalf (by DMAing
> arbitrary memory).
Is there a way to protect against rogue DMA writes (without knowing the
details of every particular piece of hardware) or is it just the price
to be paid for direct hardware access?

James

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On 22 May 2005, at 08:56, James Harper wrote:
>> Assuming you have restricted the domain to just accessing registers
> and
>> IRQs belonging to the device it controls, I think the only way would
> be
>> by programming the device to wreak havoc on its behalf (by DMAing
>> arbitrary memory).
>
> Is there a way to protect against rogue DMA writes (without knowing the
> details of every particular piece of hardware) or is it just the price
> to be paid for direct hardware access?
You need an IOMMU. Then the ''bus addresses'' you program into
the device
are checked and translated by the IOMMU when it attempts to access 
memory.

Chipset extensions to support protection from rogue devices is likely 
to appear for commodity x86 systems in the next couple of years, I 
think.

  -- Keir


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