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[PATCH] KVM: nVMX: add missing consistency checks for CR0 and CR4

Paolo Bonzini posted 1 patch 2 years, 11 months ago
There is a newer version of this series
arch/x86/kvm/vmx/nested.c | 14 +++++++++++++-
1 file changed, 13 insertions(+), 1 deletion(-)
[PATCH] KVM: nVMX: add missing consistency checks for CR0 and CR4
Posted by Paolo Bonzini 2 years, 11 months ago 
The effective values of the guest CR0 and CR4 registers may differ from
those included in the VMCS12.  In particular, disabling EPT forces
CR4.PAE=1 and disabling unrestricted guest mode forces CR0.PG=CR0.PE=1.

Therefore, checks on these bits cannot be delegated to the processor
and must be performed by KVM.

Reported-by: Reima ISHII <ishiir@g.ecc.u-tokyo.ac.jp>
Cc: stable@vger.kernel.org
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
 arch/x86/kvm/vmx/nested.c | 14 +++++++++++++-
 1 file changed, 13 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kvm/vmx/nested.c b/arch/x86/kvm/vmx/nested.c
index d93c715cda6a..43693e4772ff 100644
--- a/arch/x86/kvm/vmx/nested.c
+++ b/arch/x86/kvm/vmx/nested.c
@@ -3047,6 +3047,19 @@ static int nested_vmx_check_guest_state(struct kvm_vcpu *vcpu,
 					   vmcs12->guest_ia32_perf_global_ctrl)))
 		return -EINVAL;
 
+	if (CC((vmcs12->guest_cr0 & (X86_CR0_PG | X86_CR0_PE)) == X86_CR0_PG))
+		return -EINVAL;
+
+#ifdef CONFIG_X86_64
+	ia32e = !!(vmcs12->vm_entry_controls & VM_ENTRY_IA32E_MODE);
+#else
+	ia32e = false;
+#endif
+	if (CC(ia32e &&
+	       (!(vmcs12->guest_cr4 & X86_CR4_PAE) ||
+		!(vmcs12->guest_cr0 & X86_CR0_PG))))
+		return -EINVAL;
+
 	/*
 	 * If the load IA32_EFER VM-entry control is 1, the following checks
 	 * are performed on the field for the IA32_EFER MSR:
@@ -3058,7 +3071,6 @@ static int nested_vmx_check_guest_state(struct kvm_vcpu *vcpu,
 	 */
 	if (to_vmx(vcpu)->nested.nested_run_pending &&
 	    (vmcs12->vm_entry_controls & VM_ENTRY_LOAD_IA32_EFER)) {
-		ia32e = (vmcs12->vm_entry_controls & VM_ENTRY_IA32E_MODE) != 0;
 		if (CC(!kvm_valid_efer(vcpu, vmcs12->guest_ia32_efer)) ||
 		    CC(ia32e != !!(vmcs12->guest_ia32_efer & EFER_LMA)) ||
 		    CC(((vmcs12->guest_cr0 & X86_CR0_PG) &&
-- 
2.39.1
Re: [PATCH] KVM: nVMX: add missing consistency checks for CR0 and CR4
Posted by Sean Christopherson 2 years, 11 months ago 
On Fri, Mar 10, 2023, Paolo Bonzini wrote:
> The effective values of the guest CR0 and CR4 registers may differ from
> those included in the VMCS12.  In particular, disabling EPT forces
> CR4.PAE=1 and disabling unrestricted guest mode forces CR0.PG=CR0.PE=1.
> 
> Therefore, checks on these bits cannot be delegated to the processor
> and must be performed by KVM.
> 
> Reported-by: Reima ISHII <ishiir@g.ecc.u-tokyo.ac.jp>
> Cc: stable@vger.kernel.org
> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
> ---
>  arch/x86/kvm/vmx/nested.c | 14 +++++++++++++-
>  1 file changed, 13 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/x86/kvm/vmx/nested.c b/arch/x86/kvm/vmx/nested.c
> index d93c715cda6a..43693e4772ff 100644
> --- a/arch/x86/kvm/vmx/nested.c
> +++ b/arch/x86/kvm/vmx/nested.c
> @@ -3047,6 +3047,19 @@ static int nested_vmx_check_guest_state(struct kvm_vcpu *vcpu,
>  					   vmcs12->guest_ia32_perf_global_ctrl)))
>  		return -EINVAL;
>  
> +	if (CC((vmcs12->guest_cr0 & (X86_CR0_PG | X86_CR0_PE)) == X86_CR0_PG))
> +		return -EINVAL;
> +
> +#ifdef CONFIG_X86_64

The #ifdef isn't necessary, attempting to set for a 32-bit host should be rejected
by nested_vmx_check_controls() since nested_vmx_setup_ctls_msrs() clears the bit.
Ditto for the host logic related to VM_EXIT_HOST_ADDR_SPACE_SIZE, which looks
suspiciously similar ;-)

I'd rather delete the #ifdef in nested_vmx_check_host_state() and do something
similar here, e.g.

diff --git a/arch/x86/kvm/vmx/nested.c b/arch/x86/kvm/vmx/nested.c
index 7c4f5ca405c7..3e367ec5086a 100644
--- a/arch/x86/kvm/vmx/nested.c
+++ b/arch/x86/kvm/vmx/nested.c
@@ -2903,7 +2903,7 @@ static int nested_vmx_check_address_space_size(struct kvm_vcpu *vcpu,
 static int nested_vmx_check_host_state(struct kvm_vcpu *vcpu,
                                       struct vmcs12 *vmcs12)
 {
-       bool ia32e;
+       bool ia32e = !!(vmcs12->vm_exit_controls & VM_EXIT_HOST_ADDR_SPACE_SIZE);
 
        if (CC(!nested_host_cr0_valid(vcpu, vmcs12->host_cr0)) ||
            CC(!nested_host_cr4_valid(vcpu, vmcs12->host_cr4)) ||
@@ -2923,12 +2923,6 @@ static int nested_vmx_check_host_state(struct kvm_vcpu *vcpu,
                                           vmcs12->host_ia32_perf_global_ctrl)))
                return -EINVAL;
 
-#ifdef CONFIG_X86_64
-       ia32e = !!(vmcs12->vm_exit_controls & VM_EXIT_HOST_ADDR_SPACE_SIZE);
-#else
-       ia32e = false;
-#endif
-
        if (ia32e) {
                if (CC(!(vmcs12->host_cr4 & X86_CR4_PAE)))
                        return -EINVAL;


> +	ia32e = !!(vmcs12->vm_entry_controls & VM_ENTRY_IA32E_MODE);
> +#else
> +	ia32e = false;
> +#endif
> +	if (CC(ia32e &&
> +	       (!(vmcs12->guest_cr4 & X86_CR4_PAE) ||
> +		!(vmcs12->guest_cr0 & X86_CR0_PG))))
> +		return -EINVAL;

This is a lot easier to read IMO, and has the advantage of more precisely
identifying the failure in the tracepoint.

	if (CC(ia32e && !(vmcs12->guest_cr4 & X86_CR4_PAE)) ||
	    CC(ia32e && !(vmcs12->guest_cr4 & X86_CR0_PG)))
		return -EINVAL;

> +
>  	/*
>  	 * If the load IA32_EFER VM-entry control is 1, the following checks
>  	 * are performed on the field for the IA32_EFER MSR:
> @@ -3058,7 +3071,6 @@ static int nested_vmx_check_guest_state(struct kvm_vcpu *vcpu,
>  	 */
>  	if (to_vmx(vcpu)->nested.nested_run_pending &&
>  	    (vmcs12->vm_entry_controls & VM_ENTRY_LOAD_IA32_EFER)) {
> -		ia32e = (vmcs12->vm_entry_controls & VM_ENTRY_IA32E_MODE) != 0;
>  		if (CC(!kvm_valid_efer(vcpu, vmcs12->guest_ia32_efer)) ||
>  		    CC(ia32e != !!(vmcs12->guest_ia32_efer & EFER_LMA)) ||
>  		    CC(((vmcs12->guest_cr0 & X86_CR0_PG) &&
> -- 
> 2.39.1
>
Re: [PATCH] KVM: nVMX: add missing consistency checks for CR0 and CR4
Posted by Paolo Bonzini 2 years, 11 months ago 
On Sat, Mar 11, 2023 at 1:17 AM Sean Christopherson <seanjc@google.com> wrote:
> > @@ -3047,6 +3047,19 @@ static int nested_vmx_check_guest_state(struct kvm_vcpu *vcpu,
> >                                          vmcs12->guest_ia32_perf_global_ctrl)))
> >               return -EINVAL;
> >
> > +     if (CC((vmcs12->guest_cr0 & (X86_CR0_PG | X86_CR0_PE)) == X86_CR0_PG))
> > +             return -EINVAL;
> > +
> > +#ifdef CONFIG_X86_64
>
> The #ifdef isn't necessary, attempting to set for a 32-bit host should be rejected
> by nested_vmx_check_controls() since nested_vmx_setup_ctls_msrs() clears the bit.
> Ditto for the host logic related to VM_EXIT_HOST_ADDR_SPACE_SIZE, which looks
> suspiciously similar ;-)

Yeah, I noticed that too and decided that the idea could have been to
allow some dead code elimination on 32-bit kernels, so I copied what
the host state checks were doing. But if you prefer the more compact
way I am absolutely not going to complain.

> > +     if (CC(ia32e &&
> > +            (!(vmcs12->guest_cr4 & X86_CR4_PAE) ||
> > +             !(vmcs12->guest_cr0 & X86_CR0_PG))))
> > +             return -EINVAL;
>
> This is a lot easier to read IMO, and has the advantage of more precisely
> identifying the failure in the tracepoint.
>
>         if (CC(ia32e && !(vmcs12->guest_cr4 & X86_CR4_PAE)) ||
>             CC(ia32e && !(vmcs12->guest_cr4 & X86_CR0_PG)))
>                 return -EINVAL;

Looks good.  I squashed everything in.

Paolo

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