Re: [Xen-devel] [PATCH] xen: arm: fully implement multicall interface.

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

On Fri, 2014-03-28 at 15:01 +0000, Julien Grall wrote:
> On 03/28/2014 02:45 PM, Ian Campbell wrote:
> 
> > My feeling is that any (exploitable or otherwise) issue due to this
> > would be due to lack of proper error checking in the hypercall, and
> > would be equally accessible by a 64-bit guest.
> 
> I don't think it's exploitable. IHMO, the main point is to give a useful
> debug to the user rather than an obscure error message because the given
> pointer is invalid (perhaps by mistake).

Right.

We also want to avoid the case where it just happens to work in one
configuration (i.e. 32-on-32) but fails in another (i.e. 32-on-64).

> 
> > I'm considering whether to add an #ifndef NDEBUG check here which will
> > reject a multicall from a 32-bit guest where any of the arguments
> > (arm_hypercall_table[nr].nr_args) are non-zero in their top 32-bit. I
> > can't decide whether -EINVAL or domain_kill() would be more appropriate.
> > I'm actually leaning towards the latter.
> > 
> > Thoughts?
> 
> Killing the domain is a bit tough.

Sure, but the point is to flush out 32-bit guests which make invalid
assumptions which will be broken when they run on 64-bit vs. 32-bit Xen.

Ian.



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