Re: [Xen-devel] [PATCH v2] xsm: add device tree labeling support

[Julien Grall <julien.grall@xxxxxxxxxx>]

Hi Jan,

On 13/03/2015 09:23, Jan Beulich wrote:
> > > > On 12.03.15 at 21:42, <dgdegra@xxxxxxxxxxxxx> wrote:
> > @@ -1999,11 +2055,23 @@ int policydb_read(struct policydb *p, void *fp)
> >                           "Old xen policy does not support iomemcon");
> >                       goto bad;
> >                   }
> > -                rc = next_entry(buf, fp, sizeof(u32) *2);
> > -                if ( rc < 0 )
> > -                    goto bad;
> > -                c->u.iomem.low_iomem = le32_to_cpu(buf[0]);
> > -                c->u.iomem.high_iomem = le32_to_cpu(buf[1]);
> > +                if ( p->policyvers >= POLICYDB_VERSION_XEN_DEVICETREE )
> > +                {
> > +                    u64 b64[2];
> > +                    rc = next_entry(b64, fp, sizeof(u64) *2);
> > +                    if ( rc < 0 )
> > +                        goto bad;
> > +                    c->u.iomem.low_iomem = le64_to_cpu(b64[0]);
> > +                    c->u.iomem.high_iomem = le64_to_cpu(b64[1]);
> > +                }
> > +                else
> > +                {
> > +                    rc = next_entry(buf, fp, sizeof(u32) *2);
> > +                    if ( rc < 0 )
> > +                        goto bad;
> > +                    c->u.iomem.low_iomem = le32_to_cpu(buf[0]);
> > +                    c->u.iomem.high_iomem = le32_to_cpu(buf[1]);
> > +                }
> I might be completely wrong (knowing next to nothing about XSM),
> but how is the permissible I/O mem range tied to DT (as expressed
> by POLICYDB_VERSION_XEN_DEVICETREE)? All systems with
> valid page frame number possibly being wider than 32 bits would
> need this extension, i.e. namely also x86.
I guess the name POLICYDB_VERSION_XEN_DEVICETREE was arbitrarily chose.

The policy version 30 adds support for both device tree and 64 bits iomem.

Although, I'm wondering if we should deny policy < 30 on newer Xen 
because a truncation on the MMIO pfns may occurs and give access to the 
wrong pfn.
Regards,

--
Julien Grall

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