Re: [Xen-devel] [PATCH v7 10/10] xen/common: do not implicitly permit access to mapped I/O memory

[Julien Grall <julien.grall@xxxxxxxxxx>]

On 26/05/14 12:14, Jan Beulich wrote:
> > > > On 26.05.14 at 12:53, <julien.grall@xxxxxxxxxx> wrote:
> > On 26/05/14 11:14, Jan Beulich wrote:
> > > Or maybe I wasn't wrong - the patch context doesn't really make
> > > clear whether it's the granting or mapping operation that gets
> > > adjusted here (since an earlier patch moved the mapping one into
> > > this function).
> >            ret = -EPERM;
> > -        if ( !iomem_access_permitted(current->domain, mfn, mfn_end) )
> > +        if ( !iomem_access_permitted(d, mfn, mfn_end) )
> >                break;
> >
> >            ret = xsm_iomem_mapping(XSM_HOOK, d, mfn, mfn_end, add);
> >
> > There is an xsm_iomem_mapping just after, so the change has been done in
> > XEN_DOMCTL_memory_mapping.
> In which case I indeed stick to my original comment - it's perhaps
> best to check _both_.
Why? We may want to map the region in the guest P2M without giving the 
permission to the guest (I'm thinking about ARM passthrough case).
With your requirements, we have to call 2 hypercalls rather than one for 
memory mapping, even if we don't want to allow the guest modifying iomem 
range.
Regards,

--
Julien Grall

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