Re: [PATCH v5 2/3] KVM: nVMX: Validate the IA32_BNDCFGS on nested VM-entry

[Krish Sadhukhan]

On 11/02/2017 11:40 PM, Wanpeng Li wrote:
> 2017-11-03 14:31 GMT+08:00 Krish Sadhukhan <krish.sadhukhan@xxxxxxxxxx>:
> > On 11/02/2017 05:50 PM, Wanpeng Li wrote:
> > > From: Wanpeng Li <wanpeng.li@xxxxxxxxxxx>
> > >
> > > According to the SDM, if the "load IA32_BNDCFGS" VM-entry controls is 1,
> > > the
> > > following checks are performed on the field for the IA32_BNDCFGS MSR:
> > >    - Bits reserved in the IA32_BNDCFGS MSR must be 0.
> > >    - The linear address in bits 63:12 must be canonical.
> > >
> > > Reviewed-by: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
> > > Cc: Paolo Bonzini <pbonzini@xxxxxxxxxx>
> > > Cc: Radim KrÄmÃÅ <rkrcmar@xxxxxxxxxx>
> > > Cc: Jim Mattson <jmattson@xxxxxxxxxx>
> > > Signed-off-by: Wanpeng Li <wanpeng.li@xxxxxxxxxxx>
> > > ---
> > > v3 -> v4:
> > >    * simply condition
> > >    * use && instead of nested "if"s
> > >
> > >    arch/x86/kvm/vmx.c | 5 +++++
> > >    1 file changed, 5 insertions(+)
> > >
> > > diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
> > > index e6c8ffa..6cf3972 100644
> > > --- a/arch/x86/kvm/vmx.c
> > > +++ b/arch/x86/kvm/vmx.c
> > > @@ -10805,6 +10805,11 @@ static int check_vmentry_postreqs(struct kvm_vcpu
> > > *vcpu, struct vmcs12 *vmcs12,
> > >                          return 1;
> > >          }
> > >    +     if (kvm_mpx_supported() &&
> > > +               (is_noncanonical_address(vmcs12->guest_bndcfgs &
> > > PAGE_MASK, vcpu) ||
> > > +               (vmcs12->guest_bndcfgs & MSR_IA32_BNDCFGS_RSVD)))
> > > +                       return 1;
> > > +
> > >          return 0;
> > >    }
> > Hi Wanpeng,
> >    The SDM check is performed only when "load IA32_BNDCFGS" VM-entry control
> > is 1. But vmx_mpx_supported() returns true when both "load IA32_BNDCFGS" and
> > "store IA32_BNDCFGS" VM-entry controls are 1. Therefore your check is
> > performed when both controls are 1. Did I miss something here ?
> https://lkml.org/lkml/2017/11/2/748 Paolo hopes the simplification.
>
> Regards,
> Wanpeng Li
I got that simplification and your changes look good to me.


However, I am still curious know the reason why vmx_mpx_supported() 
returns true only when both controls are true whereas the SDM states the 
following:

   "IA32_BNDCFGS (64 bits). This field is supported only on processors 
that support either the 1-setting of the  âload IA32_BNDCFGSâ VM-entry 
control or that of the âclear IA32_BNDCFGSâ VM-exit control."

Thanks,
Krish