Messages in this thread |  | | Date | Sat, 05 Apr 2008 10:36:50 +0300 | From | Avi Kivity <> | Subject | Re: mmiotrace bug: recursive probe hit |
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Pekka Paalanen wrote: > On Sun, 30 Mar 2008 20:26:08 +0300 > Pekka Paalanen <pq@iki.fi> wrote: > > >> C) Vegard mentioned something about per-cpu page tables for kmemcheck. >> This would be the ultimate solution, because it would solve two problems: >> - recursive probe hits >> - missed events due to another cpu disarming the page for single stepping >> Would it be possible to have a single temporary per-cpu pte? >> >> I understood kmemcheck has similar issues. Of course, one could force the >> system down to a single running CPU, but that feels nasty. >> > > One more idea: > > > The catch is the instruction emulation. I see KVM has some emulation code, > but I cannot understand it without a deep study that would take me weeks. > Is that general enough to be used, or could it be generalized? > Mmiotrace, apart from executing the instruction with a modified address, > would need to extract the type of IO memory access, width and the data > read/written. And since it is dealing with IO memory, the emulation > should be very careful to access the hardware exactly like the original > instruction would have. > > Maybe also kmemcheck could use this approach, since the current approach > is very much like in mmiotrace: #pf, show page, single step, #db trap, > hide page. > > Are there other x86(_64) instruction emulation facilities in the kernel > I might use? > > Or, if the emulation cannot be used, what would it take to make at least > instruction decoding general enough so that mmiotrace could use that instead > of its own decoding? > > I fear modifying KVM emulation code is a too heavy job for me personally. >
It should not be too difficult to modify x86_emulate.c to do everything through a function vector. However there is a simpler (for you) solution: run the driver-to-be-reverse-engineered in a kvm guest, and modify kvm userspace to log accesses to mmio regions. This requires the not-yet-merged pci passthrough support. You can reverse engineer Windows drivers with this as well.
This won't work for kmemcheck smp though.
-- Any sufficiently difficult bug is indistinguishable from a feature.
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