Re: [PATCH v4 3/4] x86: nVMX: check vmcs12->guest_ia32_debugctl value given by L2

[mlevitsk]

On Fri, 2025-05-16 at 11:31 +0800, Chao Gao wrote:
> On Wed, May 14, 2025 at 08:53:52PM -0400, Maxim Levitsky wrote:
> > Check the vmcs12 guest_ia32_debugctl value before loading it, to avoid L2
> > being able to load arbitrary values to hardware IA32_DEBUGCTL.
> > 
> > Signed-off-by: Maxim Levitsky <mlevitsk@xxxxxxxxxx>
> > ---
> > arch/x86/kvm/vmx/nested.c | 4 ++++
> > arch/x86/kvm/vmx/vmx.c    | 2 +-
> > arch/x86/kvm/vmx/vmx.h    | 2 ++
> > 3 files changed, 7 insertions(+), 1 deletion(-)
> > 
> > diff --git a/arch/x86/kvm/vmx/nested.c b/arch/x86/kvm/vmx/nested.c
> > index e073e3008b16..0bda6400e30a 100644
> > --- a/arch/x86/kvm/vmx/nested.c
> > +++ b/arch/x86/kvm/vmx/nested.c
> > @@ -3193,6 +3193,10 @@ static int nested_vmx_check_guest_state(struct kvm_vcpu *vcpu,
> > 	     CC((vmcs12->guest_bndcfgs & MSR_IA32_BNDCFGS_RSVD))))
> > 		return -EINVAL;
> > 
> > +	if ((vmcs12->vm_entry_controls & VM_ENTRY_LOAD_DEBUG_CONTROLS) &&
> > +	     CC(vmcs12->guest_ia32_debugctl & ~vmx_get_supported_debugctl(vcpu, false)))
> > +		return -EINVAL;
> > +
> 
> How about grouping this check with the one against DR7 a few lines above?

Good idea, will do.
> 
> > 	if (nested_check_guest_non_reg_state(vmcs12))
> > 		return -EINVAL;
> > 
> > diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
> > index 9953de0cb32a..9046ee2e9a04 100644
> > --- a/arch/x86/kvm/vmx/vmx.c
> > +++ b/arch/x86/kvm/vmx/vmx.c
> > @@ -2179,7 +2179,7 @@ static u64 nested_vmx_truncate_sysenter_addr(struct kvm_vcpu *vcpu,
> > 	return (unsigned long)data;
> > }
> > 
> > -static u64 vmx_get_supported_debugctl(struct kvm_vcpu *vcpu, bool host_initiated)
> > +u64 vmx_get_supported_debugctl(struct kvm_vcpu *vcpu, bool host_initiated)
> > {
> > 	u64 debugctl = 0;
> > 
> > diff --git a/arch/x86/kvm/vmx/vmx.h b/arch/x86/kvm/vmx/vmx.h
> > index 6d1e40ecc024..1b80479505d3 100644
> > --- a/arch/x86/kvm/vmx/vmx.h
> > +++ b/arch/x86/kvm/vmx/vmx.h
> > @@ -413,7 +413,9 @@ static inline void vmx_set_intercept_for_msr(struct kvm_vcpu *vcpu, u32 msr,
> > 		vmx_disable_intercept_for_msr(vcpu, msr, type);
> > }
> > 
> > +
> 
> stray newline.
> 
> > void vmx_update_cpu_dirty_logging(struct kvm_vcpu *vcpu);
> > +u64 vmx_get_supported_debugctl(struct kvm_vcpu *vcpu, bool host_initiated);
> > 
> > /*
> >  * Note, early Intel manuals have the write-low and read-high bitmap offsets
> > -- 
> > 2.46.0
> > 
> > 
> 

Best regards,
	Maxim Levitsky