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

[Julien Grall <julien.grall@linaro.org>]

Hi Jan,

On 13/03/2015 09:23, Jan Beulich wrote:
>>>> On 12.03.15 at 21:42, <dgdegra@tycho.nsa.gov> 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