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

Greg KH
2020-04-07T14:56:04Z

On Tue, Apr 07, 2020 at 04:44:57PM +0200, Paolo Bonzini wrote:
> On 07/04/20 16:35, 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?
>
> It's the latter. Basically it's doing _the users_ of out-of-tree
> modules a favor by avoiding crashes of their virtual machines;
> developers need to fix them anyway.

Ok, seems kind of a heavy hammer, but oh well...

thanks for the explanation.

greg k-h