Re: [RFC PATCH 13/13] x86/Kconfig: Add Kconfig for KVM based XO

[Edgecombe, Rick P]

On Tue, 2019-10-29 at 16:36 -0700, Kees Cook wrote:
> On Thu, Oct 03, 2019 at 02:24:00PM -0700, Rick Edgecombe wrote:
> > Add CONFIG_KVM_XO for supporting KVM based execute only memory.
> 
> I would expect this config to be added earlier in the series so that the
> code being added that depends on it can be incrementally build tested...
> 
> (Also, if this is default=y, why have a Kconfig for it at all? Guests
> need to know to use this already, yes?)
> 
> -Kees
Hmm, good point. One reason could be that this requires SPARSEMEM_VMEMMAP due to
some pre-processor tricks that need a compile time known max physical address
size. So maybe someone could want KVM_GUEST and !SPARSEMEM_VMEMMAP. I'm not
sure.

> > 
> > Signed-off-by: Rick Edgecombe <rick.p.edgecombe@xxxxxxxxx>
> > ---
> >  arch/x86/Kconfig | 13 +++++++++++++
> >  1 file changed, 13 insertions(+)
> > 
> > diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
> > index 222855cc0158..3a3af2a456e8 100644
> > --- a/arch/x86/Kconfig
> > +++ b/arch/x86/Kconfig
> > @@ -802,6 +802,19 @@ config KVM_GUEST
> >  	  underlying device model, the host provides the guest with
> >  	  timing infrastructure such as time of day, and system time
> >  
> > +config KVM_XO
> > +	bool "Support for KVM based execute only virtual memory permissions"
> > +	select DYNAMIC_PHYSICAL_MASK
> > +	select SPARSEMEM_VMEMMAP
> > +	depends on KVM_GUEST && X86_64
> > +	default y
> > +	help
> > +	  This option enables support for execute only memory for KVM guests. If
> > +	  support from the underlying VMM is not detected at boot, this
> > +	  capability will automatically disable.
> > +
> > +	  If you are unsure how to answer this question, answer Y.
> > +
> >  config PVH
> >  	bool "Support for running PVH guests"
> >  	---help---
> > -- 
> > 2.17.1
> > 
> 
>