Re: [Xen-devel] [PATCH 16/18] arch/x86: use XSM hooks for get_pg_owner access checks

[Daniel De Graaf <dgdegra@xxxxxxxxxxxxx>]

On 08/07/2012 02:55 AM, Jan Beulich wrote:
>>>> On 06.08.12 at 18:29, Daniel De Graaf <dgdegra@xxxxxxxxxxxxx> wrote:
>> On 08/06/2012 11:26 AM, Jan Beulich wrote:
>>>>>> On 06.08.12 at 16:32, Daniel De Graaf <dgdegra@xxxxxxxxxxxxx> wrote:
>>>> +static XSM_DEFAULT(int, mmuext_op) (struct domain *d, struct domain *f)
>>>> +{
>>>> +    if ( d != f && !IS_PRIV_FOR(d, f) )
>>>> +        return -EPERM;
>>>
>>> ... Dom0 is neither privileged for DOM_IO nor for DOM_XEN.
>>
>> Actually, it is. IS_PRIV_FOR returns true for any domain when called from an
>> IS_PRIV domain.
> 
> That's a side effect of the current way of handling this, not
> something that is either logical or designed to be that way (it
> certainly is bogus even now for DOM_XEN, and with
> disaggregation - afaiu your plans - it'll also become bogus for
> DOM_IO, where right now one could consider it half-way
> correct).
> 
> Jan
> 

In that case, I think it would make sense to modify these XSM hooks
when IS_PRIV_FOR is changed to not short-circuit on DOM_IO/DOM_XEN.
If you're suggesting changing the condition to something like
  ( d != f && !(IS_PRIV_FOR(d, f) || IS_PRIV(d)) )
I could do that, but I think that type of change would be best done
in another patch actually making IS_PRIV_FOR(dom0, DOM_XEN) == false.

-- 
Daniel De Graaf
National Security Agency

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