Re: [PATCH] sysctl: XSM hook should not cause XEN_SYSCTL_getdomaininfolist to (appear to) fail

[Roger Pau Monné <roger.pau@xxxxxxxxxx>]

On Tue, May 02, 2023 at 10:27:39AM +0100, Andrew Cooper wrote:
> On 02/05/2023 8:17 am, Jan Beulich wrote:
> > The hook being able to deny access to data for certain domains means
> > that no caller can assume to have a system-wide picture when holding the
> > results.
> >
> > Wouldn't it make sense to permit the function to merely "count" domains?
> > While racy in general (including in its present, "normal" mode of
> > operation), within a tool stack this could be used as long as creation
> > of new domains is suppressed between obtaining the count and then using
> > it.
> 
> This would not be the first example of the XSM hooks being tantamount to
> useless.  I doubt it will be the last either.
> 
> With the rest of Alejandro's series in place, all requests for a single
> domid's worth of info use the domctl, and all requests for all domains
> use the systctl.
> 
> 
> As a result, we can retrofit some sanity and change the meaning of the
> XSM hook here for the sysctl, to mean "can see a systemwide view" (or
> not).  This moves the check out of the loop, and fixes the behaviour.

Don't we still need some kind of loop, as the current getdomaininfo()
XSM hook expects a domain parameter in order to check whether the
caller has permissions over it?

Or we plan to introduce a new hook that reports whether a caller has
permissions over all domains?

Thanks, Roger.