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

[Volodymyr Babchuk <vlad.babchuk@xxxxxxxxx>]

Hello Julien,



On 30 November 2016 at 17:29, Julien Grall <julien.grall@xxxxxxx> wrote:
[...]
> I think we can distinct two places where the PL011 could be emulated:
> in the hypervisor, or outside the hypervisor.
>
> Emulating the UART in the hypervisor means that we take the risk to increase
> to the attack surface of Xen if there is a bug in the emulation code. The
> attack surface could be reduced by emulating the UART in another exception
> level (e.g EL1, EL0) but still under the control of the hypervisor. Usually
> the guest is communicating between with xenconsoled using a ring. For the
> first console this could be discovered using hypercall HVMOP_get_param. For
> the second and onwards, it described in xenstore. I would not worry too much
> about emulating multiple PL011s, so we could implement the PV frontend in
> Xen.
>
[...]

> I would lean towards the first solution if we implement all the security
> safety I mentioned. Although, the second solution would be a good move if we
> decide to implement more devices (e.g RTC, pflash) in the future.
>
> Do you have any opinions?
Looks like this topic have some in common with OP-TEE thread. I like
first solution, because if there will be easy and reliable way to run
code in XEN's EL1/EL0, then this will be ideal solution for TEE
emulation/mediation layer.
So, if you'll choose this way, please bear in mind other uses, like
TEE emulation.

-- 
WBR Volodymyr Babchuk aka lorc [+380976646013]
mailto: vlad.babchuk@xxxxxxxxx

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