Re: [Xen-devel] [PATCH 09/11] evtchn: implement EVTCHNOP_set_limit

[Daniel De Graaf <dgdegra@xxxxxxxxxxxxx>]

On 09/13/2013 12:56 PM, David Vrabel wrote:
> From: David Vrabel <david.vrabel@xxxxxxxxxx>
>
> Add max_evtchn_port to struct domain as the maximum port number that a
> domain may bind.  Allow a suitably privileged domain to set this limit
> so it may restrict the other domain's usage of Xen resources for event
> channels (primarily global mapping entries for the shared data
> structures).
>
> The default values for this limit is unlimited for control domains or
> NR_EVENT_CHANNELS - 1 for other domains.  These defaults ensure that no
> domain will regress in the number of event channels they may use.
>
> If a domain is expected to use the FIFO-based event channel ABI, a
> toolstack may wish to set the limit to 1023 or lower to ensure a
> minimum number of global mapping entries is used.
>
> Signed-off-by: David Vrabel <david.vrabel@xxxxxxxxxx>
> Cc: Daniel De Graaf <dgdegra@xxxxxxxxxxxxx>
This allows device model domains to adjust the limit of their target
domain arbitrarily; I think it makes more sense for this to be XSM_PRIV
so that only dom0 can adjust it, similar to max_mem. Control domains
will already need an explicit XSM policy that can address this as a
fine-grained permission.

The new XSM hook also needs to be added to xsm/dummy.c. Adding a FLASK
hook and permission similar to the one for evtchn_reset would also be
nice, but that may fit better in a later patch that adds this operation
to the example security policy.

With the check changed to XSM_PRIV and a set_to_dummy_if_null line added
to xsm/dummy.c, Acked-by: Daniel De Graaf <dgdegra@xxxxxxxxxxxxx>

--
Daniel De Graaf
National Security Agency

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