Re: [Xen-devel] [PATCH 4/6] xsm: flask: change the interface and default policy for xsm_map_gmfn_foregin

[Stefano Stabellini <sstabellini@xxxxxxxxxx>]

On Wed, 23 Aug 2017, Jan Beulich wrote:
> >>> On 22.08.17 at 20:08, <blackskygg@xxxxxxxxx> wrote:
> > The original xsm_map_gmfn_foregin policy checks if source domain has the 
> > proper
> > privileges over the target domain. Under this policy, it's not allowed if a 
> > Dom0
> > wants to map pages from one DomU to another, this restricts some useful yet 
> > not
> > dangerous usages of the API, such as sharing pages among DomU's by calling
> > XENMEM_add_to_physmap from Dom0.
> > 
> > Change the policy to: IIF current domain has the proper privilege on the
> > target domain and source domain, grant the access.
> 
> You say "and here", yet ...
> 
> > --- a/xen/include/xsm/dummy.h
> > +++ b/xen/include/xsm/dummy.h
> > @@ -525,10 +525,12 @@ static XSM_INLINE int 
> > xsm_remove_from_physmap(XSM_DEFAULT_ARG struct domain *d1,
> >      return xsm_default_action(action, d1, d2);
> >  }
> >  
> > -static XSM_INLINE int xsm_map_gmfn_foreign(XSM_DEFAULT_ARG struct domain 
> > *d, struct domain *t)
> > +static XSM_INLINE int xsm_map_gmfn_foreign(XSM_DEFAULT_ARG struct domain 
> > *cd,
> > +                                           struct domain *d, struct domain 
> > *t)
> >  {
> >      XSM_ASSERT_ACTION(XSM_TARGET);
> > -    return xsm_default_action(action, d, t);
> > +    return xsm_default_action(action, cd, d) ||
> > +        xsm_default_action(action, cd, t);
> >  }
> 
> ... you use "or" here and ...
> 
> > --- a/xen/xsm/flask/hooks.c
> > +++ b/xen/xsm/flask/hooks.c
> > @@ -1165,9 +1165,11 @@ static int flask_remove_from_physmap(struct domain 
> > *d1, struct domain *d2)
> >      return domain_has_perm(d1, d2, SECCLASS_MMU, MMU__PHYSMAP);
> >  }
> >  
> > -static int flask_map_gmfn_foreign(struct domain *d, struct domain *t)
> > +static int flask_map_gmfn_foreign(struct domain *cd,
> > +                                  struct domain *d, struct domain *t)
> >  {
> > -    return domain_has_perm(d, t, SECCLASS_MMU, MMU__MAP_READ | 
> > MMU__MAP_WRITE);
> > +    return domain_has_perm(cd, d, SECCLASS_MMU, MMU__MAP_READ | 
> > MMU__MAP_WRITE) ||
> > +        domain_has_perm(cd, t, SECCLASS_MMU, MMU__MAP_READ | 
> > MMU__MAP_WRITE);
> >  }
> 
> ... here. A domain can't have XSM_TARGET permission over two
> other domains, so what you want to do here can't work at all,
> afaict.

It would work with XSM_TARGET if cd == d, and cd has XSM_TARGET
permission over t (current case). Otherwise, it would work if cd is
XSM_PRIV (Zhongze's case). Did I get it wrong?

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