Re: [PATCH 1/2] xsm: add ability to elevate a domain to privileged

[Roger Pau Monné <roger.pau@xxxxxxxxxx>]

On Wed, Mar 30, 2022 at 07:05:48PM -0400, Daniel P. Smith wrote:
> There are now instances where internal hypervisor logic needs to make resource
> allocation calls that are protected 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 introduces a pair
> of privilege escalation and demotion functions that will make a system domain
> privileged and then remove that privilege.
> 
> Signed-off-by: Daniel P. Smith <dpsmith@xxxxxxxxxxxxxxxxxxxx>
> ---
>  xen/include/xsm/xsm.h | 22 ++++++++++++++++++++++

I'm not sure this needs to be in xsm code, AFAICT it could live in a
more generic file.

>  1 file changed, 22 insertions(+)
> 
> diff --git a/xen/include/xsm/xsm.h b/xen/include/xsm/xsm.h
> index e22d6160b5..157e57151e 100644
> --- a/xen/include/xsm/xsm.h
> +++ b/xen/include/xsm/xsm.h
> @@ -189,6 +189,28 @@ struct xsm_operations {
>  #endif
>  };
>  
> +static always_inline int xsm_elevate_priv(struct domain *d)

I don't think it needs to be always_inline, using just inline would be
fine IMO.

Also this needs to be __init.

> +{
> +    if ( is_system_domain(d) )
> +    {
> +        d->is_privileged = true;
> +        return 0;
> +    }
> +

I would add an ASSERT_UNREACHABLE(); here, I don't think we have any
use case for trying to elevate the privileges of a non-system domain.

Thanks, Roger.