Re: [Xen-devel] [PATCH v2 1/3] xsm/xen_version: Add XSM for the xen_version hypercall.

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 12.01.16 at 17:37, <konrad.wilk@xxxxxxxxxx> wrote:
> On Mon, Jan 11, 2016 at 09:17:57AM -0700, Jan Beulich wrote:
>> >>> On 11.01.16 at 17:01, <konrad.wilk@xxxxxxxxxx> wrote:
>> > On Mon, Jan 11, 2016 at 02:02:54AM -0700, Jan Beulich wrote:
>> >> >>> On 08.01.16 at 18:31, <konrad.wilk@xxxxxxxxxx> wrote:
>> >> >> >> > The rest: XENVER_[version|capabilities|
>> >> >> >> > parameters|get_features|page_size|guest_handle] behave
>> >> >> >> > as before - allowed by default for all guests.
>> >> >> >> > 
>> >> >> >> > This is with the XSM default policy and with the dummy ones.
>> >> >> >> 
>> >> >> >> And with a non-default policy you now ignore one of the latter
>> >> >> >> ops to also get denied.
>> >> >> > 
>> >> >> > No, but that is due to the 'deny' being only checked for certain 
>> >> >> > subops.
>> >> >> 
>> >> >> To me this reply seems contradictory in itself: The "no" doesn't
>> >> >> seem to match up with the rest.
>> >> >> 
>> >> >> > I think what you are saying is that for XENVER_[version|capabilities|
>> >> >> > parameters|get_features|page_size|guest_handle] we should not have 
>> >> >> > any
>> >> >> > XSM checks as they serve no purpose (which is what I had in the 
>> >> >> > earlier
>> >> >> > versions of this patch). However Andrew mentioned that he would
>> >> >> > like _ALL_ of the sub-ops to be checked for.
>> >> >> 
>> >> >> And I agree with Andrew, hence my earlier comment above (with
>> >> >> the reply I can't really make sense of).
>> >> > 
>> >> > I am all confused now.
>> >> > 
>> >> > There are two parts here:
>> >> >  a) The XSM checks - which allow the XENVER_version..XENVER_guest_handle
>> >> >    without any hinderance. For XENVER_commandline and XENVER_buildid
>> >> >    they are evaluated.
>> >> > 
>> >> >  b) Acting on the XSM check. For most of them we cannot actually return
>> >> >    -EFAULT and MUST return either an valid value or some form of a 
>> >> > string.
>> >> >    
>> >> >    The ones for which we could return '<denied>' were changeset, 
> compile_info,
>> >> >    commandline, extraversion. To make it simpler we only do it for
>> >> >    commandline.
>> >> > 
>> >> > In essence we have an XSM check which is ignored by all XENVER_ subops
>> >> > except commandline (and build_id in later patch).
>> >> > 
>> >> > I think both of you are OK with that?
>> >> 
>> >> Iirc Andrew's request was to honor XSM denies on any sub-op
>> >> when a non-default policy is in place. Whereas in default mode
>> >> only command line and build id are the ones clearly needing
>> >> restricting. Which won't be possible if you ignore the return
>> >> value of the XSM check in some of the cases.
>> > 
>> > That means we need two (as earlier patches had it) version labels.
>> > One for the command_line and build_id (version_priv) and one for
>> > the rest (version_use). By default version_use would be available
>> > to every guest. If a non-default policy wants to mess with it - that is OK.
>> 
>> That would seem a little too coarse grained. Why can't we keep it
>> at the sub-op level, just that the default is "OK" for everything
>> except the two?
> 
> So you thinking have a whole new XSM 'class' for this hypercall?

Yes, subject to Daniel's input it seems to me that's the only way
providing the necessary granularity.

Jan


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