Re: [PATCH 2/3 v4] KVM: nSVM: Check that MBZ bits in CR3 and CR4 are not set on vmrun of nested guests

[Paolo Bonzini <pbonzini@redhat.com>]

On 08/07/20 02:39, Krish Sadhukhan wrote:
> +extern int kvm_valid_cr4(struct kvm_vcpu *vcpu, unsigned long cr4);
> +

This should be added in x86.h, not here.

> +static bool nested_vmcb_checks(struct vcpu_svm *svm, struct vmcb *vmcb)
>  {
>  	if ((vmcb->save.efer & EFER_SVME) == 0)
>  		return false;
> @@ -231,6 +233,22 @@ static bool nested_vmcb_checks(struct vmcb *vmcb)
>  	    (vmcb->save.cr0 & X86_CR0_NW))
>  		return false;
>  
> +	if (!is_long_mode(&(svm->vcpu))) {
> +		if (vmcb->save.cr4 & X86_CR4_PAE) {
> +			if (vmcb->save.cr3 & MSR_CR3_LEGACY_PAE_RESERVED_MASK)
> +				return false;
> +		} else {
> +			if (vmcb->save.cr3 & MSR_CR3_LEGACY_RESERVED_MASK)
> +				return false;
> +		}
> +	} else {
> +		if ((vmcb->save.cr4 & X86_CR4_PAE) &&
> +		    (vmcb->save.cr3 & MSR_CR3_LONG_RESERVED_MASK))
> +			return false;
> +	}

is_long_mode here is wrong, as it refers to the host.

You need to do something like this:

diff --git a/arch/x86/kvm/svm/nested.c b/arch/x86/kvm/svm/nested.c
index 385461496cf5..cbbab83f19cc 100644
--- a/arch/x86/kvm/svm/nested.c
+++ b/arch/x86/kvm/svm/nested.c
@@ -222,8 +222,9 @@ static bool nested_vmcb_check_controls(struct vmcb_control_area *control)
 	return true;
 }
 
-static bool nested_vmcb_checks(struct vmcb *vmcb)
+static bool nested_vmcb_checks(struct vcpu_svm *svm, struct vmcb *vmcb)
 {
+	bool nested_vmcb_lma;
 	if ((vmcb->save.efer & EFER_SVME) == 0)
 		return false;
 
@@ -234,6 +237,27 @@ static bool nested_vmcb_checks(struct vmcb *vmcb)
 	if (!kvm_dr6_valid(vmcb->save.dr6) || !kvm_dr7_valid(vmcb->save.dr7))
 		return false;
 
+	nested_vmcb_lma = 
+	        (vmcb->save.efer & EFER_LME) &&
+                (vmcb->save.cr0 & X86_CR0_PG);
+
+	if (!nested_vmcb_lma) {
+		if (vmcb->save.cr4 & X86_CR4_PAE) {
+			if (vmcb->save.cr3 & MSR_CR3_LEGACY_PAE_RESERVED_MASK)
+				return false;
+		} else {
+			if (vmcb->save.cr3 & MSR_CR3_LEGACY_RESERVED_MASK)
+				return false;
+		}
+	} else {
+		if (!(vmcb->save.cr4 & X86_CR4_PAE) ||
+		    !(vmcb->save.cr0 & X86_CR0_PE) ||
+		    (vmcb->save.cr3 & MSR_CR3_LONG_RESERVED_MASK))
+			return false;
+	}
+	if (kvm_valid_cr4(&(svm->vcpu), vmcb->save.cr4))
+		return false;
+
 	return nested_vmcb_check_controls(&vmcb->control);
 }
 
which also takes care of other CR0/CR4 checks in the APM.

I'll test this a bit more and queue it.  Are you also going to add
more checks in svm_set_nested_state?

Paolo