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0 pointsAaronFriel12y ago0 comments

It isn't a software issue - it's a hardware issue. FireWire and these other specifications require direct memory access. If you plug in a device and it emulates something that requests DMA from the hardware, your machine can be owned.

The solution is an IO memory management unit with virtualized access to physical memory. I am not sure how you can actually enforce this to devices on the bus though.

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2 comments · 2 top-level

__david__12y ago

The solution is easier than that: only open up the appropriate buffers to DMA. It doesn't need to be virtualized, it just needs to be bounds checked.

Maybe I'm spoiled by good hardware, but when I wrote FireWire drivers for embedded systems, we didn't just open up DMA access to RAM willy-nilly.

I honestly don't know enough about OHCI to know what the hardware setup is like, but I suspect it's just laziness.

nine_k12y ago

If it requires a driver (and it does), it is a software issue. Just having a FireWire port, without a driver, is not enough.

So a sane OS should just not allow to initialize a DMA transfer from a newly attached device until a user with enough privilege allows it.

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