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SubjectRe: [RFC PATCH 13/13] x86/Kconfig: Add Kconfig for KVM based XO
On Wed, Oct 30, 2019 at 12:01:18AM +0000, Edgecombe, Rick P wrote:
> 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.

Good point about the combination of other CONFIGs. All the more reason
to move it earlier, though.

-Kees

>
> > >
> > > Signed-off-by: Rick Edgecombe <rick.p.edgecombe@intel.com>
> > > ---
> > > 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
> > >
> >
> >

--
Kees Cook

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