Re: [Xen-devel] [PATCH v6 7/8] xen/arm: don't iomem_permit_access for reserved-memory regions

[Stefano Stabellini <sstabellini@xxxxxxxxxx>]

On Fri, 16 Aug 2019, Julien Grall wrote:
> On 16/08/2019 00:36, Stefano Stabellini wrote:
> > Don't allow reserved-memory regions to be remapped into any unprivileged
> > guests, until reserved-memory regions are properly supported in Xen. For
> > now, do not call iomem_permit_access on them, because giving
> > iomem_permit_access to dom0 means that the toolstack will be able to
> > assign the region to a domU.
> > 
> > Signed-off-by: Stefano Stabellini <stefanos@xxxxxxxxxx>
> > ---
> > 
> > Changes in v6:
> > - compare against "/reserved-memory/"
> > 
> > Changes in v5:
> > - fix check condition
> > - use strnicmp
> > - return error
> > - improve commit message
> > 
> > Changes in v4:
> > - compare the parent name with reserved-memory
> > - use dt_node_cmp
> > 
> > Changes in v3:
> > - new patch
> > ---
> >   xen/arch/arm/domain_build.c | 24 ++++++++++++++++--------
> >   1 file changed, 16 insertions(+), 8 deletions(-)
> > 
> > diff --git a/xen/arch/arm/domain_build.c b/xen/arch/arm/domain_build.c
> > index 4c8404155a..673ffa453f 100644
> > --- a/xen/arch/arm/domain_build.c
> > +++ b/xen/arch/arm/domain_build.c
> > @@ -1155,15 +1155,23 @@ static int __init map_range_to_domain(const struct
> > dt_device_node *dev,
> >       bool need_mapping = !dt_device_for_passthrough(dev);
> >       int res;
> >   -    res = iomem_permit_access(d, paddr_to_pfn(addr),
> > -                              paddr_to_pfn(PAGE_ALIGN(addr + len - 1)));
> > -    if ( res )
> > +    /*
> > +     * Don't give iomem permissions for reserved-memory ranges to domUs
> 
> In upstream Xen, this is only called for Dom0. So what are you referring to?
> 
> > +     * until reserved-memory support is complete.
> 
> But as I pointed out before reserved-memory support is not going to happen via
> iomem. This is an abuse of the interface.
> 
> > +     */
> 
> A better comment would be:
> 
> "reserved-memory regions are RAM carved out for special purpose. They are not
> MMIO and therefore a domain should not be able to manage them via the IOMEM
> interface".

Thank you for providing the comment. I'll use your version.


> > +    if ( strnicmp(dt_node_full_name(dev), "/reserved-memory/",
> > +         strlen("/reserved-memory/")) != 0 )
> >       {
> > -        printk(XENLOG_ERR "Unable to permit to dom%d access to"
> > -               " 0x%"PRIx64" - 0x%"PRIx64"\n",
> > -               d->domain_id,
> > -               addr & PAGE_MASK, PAGE_ALIGN(addr + len) - 1);
> > -        return res;
> > +        res = iomem_permit_access(d, paddr_to_pfn(addr),
> > +                paddr_to_pfn(PAGE_ALIGN(addr + len - 1)));
> > +        if ( res )
> > +        {
> > +            printk(XENLOG_ERR "Unable to permit to dom%d access to"
> > +                    " 0x%"PRIx64" - 0x%"PRIx64"\n",
> > +                    d->domain_id,
> > +                    addr & PAGE_MASK, PAGE_ALIGN(addr + len) - 1);
> > +            return res;
> > +        }
> >       }
> >         if ( need_mapping )
> > 
> 
> Cheers,
> 
> -- 
> Julien Grall
> 

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