Re: [RFC PATCH 1/1] xsm: allows system domains to allocate evtchn

[Stefano Stabellini <sstabellini@xxxxxxxxxx>]

On Mon, 28 Mar 2022, Daniel P. Smith wrote:
> During domain construction under dom0less and hyperlaunch it is necessary to
> allocate at least the event channel for xenstore and potentially the event
> channel for the core console. When dom0less and hyperlaunch are doing their
> construction logic they are executing under the idle domain context. The idle
> domain is not a privileged domain, it is not the target domain, and as a 
> result
> under the current default XSM policy is not allowed to allocate the event
> channel.
> 
> This patch only addresses the event channel situation by adjust the default 
> XSM
> policy for xsm_evtchn_unbound to explicitly allow system domains to be able to
> make the allocation call.
> 
> Signed-off-by: Daniel P. Smith <dpsmith@xxxxxxxxxxxxxxxxxxxx>

Reviewed-by: Stefano Stabellini <sstabellini@xxxxxxxxxx>
Tested-by: Stefano Stabellini <sstabellini@xxxxxxxxxx>


> ---
>  xen/common/event_channel.c | 4 ++--
>  xen/include/xsm/dummy.h    | 8 ++++++--
>  2 files changed, 8 insertions(+), 4 deletions(-)
> 
> diff --git a/xen/common/event_channel.c b/xen/common/event_channel.c
> index ffb042a241..c9c3876ee9 100644
> --- a/xen/common/event_channel.c
> +++ b/xen/common/event_channel.c
> @@ -306,7 +306,7 @@ static int evtchn_alloc_unbound(evtchn_alloc_unbound_t 
> *alloc)
>          ERROR_EXIT_DOM(port, d);
>      chn = evtchn_from_port(d, port);
>  
> -    rc = xsm_evtchn_unbound(XSM_TARGET, d, chn, alloc->remote_dom);
> +    rc = xsm_evtchn_unbound(XSM_OTHER, d, chn, alloc->remote_dom);
>      if ( rc )
>          goto out;
>  
> @@ -1366,7 +1366,7 @@ int alloc_unbound_xen_event_channel(
>          goto out;
>      chn = evtchn_from_port(ld, port);
>  
> -    rc = xsm_evtchn_unbound(XSM_TARGET, ld, chn, remote_domid);
> +    rc = xsm_evtchn_unbound(XSM_OTHER, ld, chn, remote_domid);
>      if ( rc )
>          goto out;
>  
> diff --git a/xen/include/xsm/dummy.h b/xen/include/xsm/dummy.h
> index 58afc1d589..bd31ce43f9 100644
> --- a/xen/include/xsm/dummy.h
> +++ b/xen/include/xsm/dummy.h
> @@ -294,8 +294,12 @@ static XSM_INLINE int cf_check 
> xsm_claim_pages(XSM_DEFAULT_ARG struct domain *d)
>  static XSM_INLINE int cf_check xsm_evtchn_unbound(
>      XSM_DEFAULT_ARG struct domain *d, struct evtchn *chn, domid_t id2)
>  {
> -    XSM_ASSERT_ACTION(XSM_TARGET);
> -    return xsm_default_action(action, current->domain, d);
> +    XSM_ASSERT_ACTION(XSM_OTHER);
> +
> +    if ( is_system_domain(current->domain) )
> +        return xsm_default_action(XSM_HOOK, current->domain, d);
> +    else
> +        return xsm_default_action(XSM_TARGET, current->domain, d);
>  }
>  
>  static XSM_INLINE int cf_check xsm_evtchn_interdomain(
> -- 
> 2.20.1
>