Re: [PATCH 1/2] xsm: create idle domain privieged and demote after setup

[Jason Andryuk <jandryuk@xxxxxxxxx>]

On Wed, Apr 20, 2022 at 1:02 PM Daniel P. Smith
<dpsmith@xxxxxxxxxxxxxxxxxxxx> wrote:
>
> There are now instances where internal hypervisor logic needs to make resource
> allocation calls that are protectd by XSM checks. The internal hypervisor 
> logic
> is represented a number of system domains which by designed are represented by
> non-privileged struct domain instances. To enable these logic blocks to
> function correctly but in a controlled manner, this commit changes the idle
> domain to be created as a privileged domain under the default policy, which is
> inherited by the SILO policy, and demoted before transitioning to running. A
> new XSM hook, xsm_transition_running, is introduced to allow each XSM policy
> type to demote the idle domain appropriately for that policy type.
>
> For flask a stub is added to ensure that flask policy system will function
> correctly with this patch until flask is extended with support for starting 
> the
> idle domain privileged and properly demoting it on the call to
> xsm_transtion_running.
>
> Signed-off-by: Daniel P. Smith <dpsmith@xxxxxxxxxxxxxxxxxxxx>
> ---

> diff --git a/xen/arch/x86/setup.c b/xen/arch/x86/setup.c
> index 6f20e17892..72695dcb07 100644
> --- a/xen/arch/x86/setup.c
> +++ b/xen/arch/x86/setup.c
> @@ -621,6 +621,12 @@ static void noreturn init_done(void)
>      void *va;
>      unsigned long start, end;
>
> +    xsm_transition_running();
> +
> +    /* Ensure idle domain was not left privileged */
> +    if ( current->domain->is_privileged )
> +        panic("idle domain did not properly transition from setup 
> privilege\n");

Checking immediately after the XSM hook seems redundant, though I
guess having a sanity check isn't harmful.

>  static void cf_check flask_domain_free_security(struct domain *d)
>  {
>      struct domain_security_struct *dsec = d->ssid;
> @@ -1766,6 +1780,7 @@ static int cf_check flask_argo_send(
>  #endif
>
>  static const struct xsm_ops __initconst_cf_clobber flask_ops = {
> +    .transition_running = flask_domain_runtime_security,

I'd prefer flask_transition_running.  That way grep for the hook name
also finds the flask implementation.

Regards,
Jason