Re: [PATCH 0/4] x86: enable User-Mode Instruction Prevention

[Ricardo Neri]

On Tue, 2016-11-08 at 07:34 -0800, Andy Lutomirski wrote:
> > Would it not be better to emulate these instructions for them? What
> way
> > we can verify they're not malicious.
> 
> Forget malice -- if they are really needed for some silly vm86-using
> program, let's trap them and emulate them so they return dummy values.
> 
> Also, keep in mind that vm86 is already effectively gated behind a
> sysctl for non-root.  I think the default should be that, if root has
> enabled vm86, it should work.

Then should I keep UMIP enabled by default and still provide an option
to disable it via a kernel parameter?

Also, a third option, umip=novm86 would "disable" UMIP in vm86 tasks.
Under the new approach (of emulating the impacted instructions), this
option, a #GP fault would still be generated but the actual values of
GDT/LDT/IDT/MSW would be passed to user space. Does this make sense?

Thanks and BR,
Ricardo