Re: [Xen-devel] [Xen-users] xc_hvm_inject_trap() failing for int3 traps under Xen 4.2.2

[George Dunlap <George.Dunlap@xxxxxxxxxxxxx>]

On Fri, Jun 7, 2013 at 4:51 PM, Steven Maresca <steve@xxxxxxxxxxxx> wrote:
> Tony,
>
> I can confirm INT3 re-injection does work on 4.2.x and 4.3, but the
> problem you observed is certainly present.
>
> As suggested, it was necessary when invoking xc_hvm_inject_trap to
> specify the 1-byte instruction length for 0xCC (without which the VM
> was intentionally crashed by Xen).
>
> In this case, there's no need to inspect the actual instruction
> referenced by the IP because it seems the trap is only fired for the
> one-byte variant (0xCD03 of course works properly, but no event is
> emitted).
>
> Mirroring your experience with 4.1.2, for my testing on 4.2+ the
> return of xc_hvm_inject_trap is also always non-zero even for
> successful re-injection..whether that's intended is another question.
>
> Steve
>
> NOTE: I would definitely consider it a bug that the xen-access.c
> example crashes guests when attempting to use the INT3
> mode...non-critical for most users, but nevertheless.

I'm having a bit of trouble finding the conclusion here.

So it seems the problem is that if a *guest* is doing int3
instructions, that will interfere with the ability of the debugger to
use int3 to do introspection -- is that right?

If anyone on this thread were able to make and test a proper fix, I'm
sure we would all appreciate it. :-)

At this point it would definitely not be a release blocker, but we
would obviously like to have it fixed.

 -George

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