Re: [Xen-devel] Xen ARM - Exposing a PL011 to the guest

[Julien Grall <julien.grall@xxxxxxx>]

Hi Stefano,

On 20/12/2016 22:33, Stefano Stabellini wrote:
> On Tue, 20 Dec 2016, Christoffer Dall wrote:
> > On Mon, Dec 19, 2016 at 12:24:18PM -0800, Stefano Stabellini wrote:
> > > On Mon, 19 Dec 2016, Christoffer Dall wrote:
> > > > On Fri, Dec 16, 2016 at 05:03:13PM +0000, Julien Grall wrote:
> hvm_param is very easy to use, but the guest has access to it too. If we
> used hvm_param, we would need to make sure that the guest is not able to
> cause any damage.
>
> On the other hand, if we introduced a new hypercall, then we wouldn't
> have to worry about the guest. But it would be another new hypercall.
>
> Another option we would be to introduce a set of hvm_params which are
> not guest-readable. Today all hvm_params are XSM_TARGET, so both "self"
> and Dom0 (and stubdoms) can issue hvm_params. We could restrict a few of
> them to XSM_DM_PRIV, which only allow Dom0 (and stubdoms) to issue them.
> It would be as simple as changing the xsm check for a subset of them.
> Obviously we would clearly document which are which.
>
> Thoughts?
That would work. FWIW, x86 is already restricting the access to some HVM 
parameter (see hvm_allow_set_param).
Cheers,

--
Julien Grall

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