Re: [PATCH 3/4] x86,module: Detect VMX vs SLD conflicts

Peter Zijlstra
2020-04-07T15:24:40Z

On Tue, Apr 07, 2020 at 04:35:43PM +0200, Greg KH wrote:
> On Tue, Apr 07, 2020 at 01:02:39PM +0200, Peter Zijlstra wrote:
> > It turns out that with Split-Lock-Detect enabled (default) any VMX
> > hypervisor needs at least a little modification in order to not blindly
> > inject the #AC into the guest without the guest being ready for it.
> >
> > Since there is no telling which module implements a hypervisor, scan
> > all out-of-tree modules' text and look for VMX instructions and refuse
> > to load it when SLD is enabled (default) and the module isn't marked
> > 'sld_safe'.
> >
> > Hypervisors, which have been modified and are known to work correctly,
> > can add:
> >
> > MODULE_INFO(sld_safe, "Y");
> >
> > to explicitly tell the module loader they're good.
>
> What's to keep any out-of-tree module from adding this same module info
> "flag" and just lie about it? Isn't that what you are trying to catch
> here, or is it a case of, "if you lie, your code will break" as well?

If they lie they get to keep both pieces.

The thing I worry about is them lying about "intree", is there anything
that avoids that?