Re: [PATCH 2/5 v6] nSVM: Check addresses of MSR and IO permission maps

[Sean Christopherson <seanjc@google.com>]

On Thu, Apr 01, 2021, Krish Sadhukhan wrote:
> According to section "Canonicalization and Consistency Checks" in APM vol 2,
> the following guest state is illegal:
> 
>     "The MSR or IOIO intercept tables extend to a physical address that
>      is greater than or equal to the maximum supported physical address."
> 
> Suggested-by: Paolo Bonzini <pbonzini@redhat.com>
> Signed-off-by: Krish Sadhukhan <krish.sadhukhan@oracle.com>
> ---
>  arch/x86/kvm/svm/nested.c | 23 +++++++++++++++++++----
>  1 file changed, 19 insertions(+), 4 deletions(-)
> 
> diff --git a/arch/x86/kvm/svm/nested.c b/arch/x86/kvm/svm/nested.c
> index fb204eaa8bb3..b3988b3a3fd5 100644
> --- a/arch/x86/kvm/svm/nested.c
> +++ b/arch/x86/kvm/svm/nested.c
> @@ -231,7 +231,15 @@ static bool svm_get_nested_state_pages(struct kvm_vcpu *vcpu)
>  	return true;
>  }
>  
> -static bool nested_vmcb_check_controls(struct vmcb_control_area *control)
> +static bool nested_svm_check_bitmap_pa(struct kvm_vcpu *vcpu, u64 pa,
> +				       u32 size)

No need to put "u32 size)" on a separate line.

> +{
> +	u64 last_pa = PAGE_ALIGN(pa) + size - 1;

Space between declaration and code.  A comment about the silliness of hardware
silently ignoring bits 11:0 would also be nice.

> +	return (kvm_vcpu_is_legal_gpa(vcpu, last_pa));

This fails to handle the case where "pa == -1", as the above will wrap to a
legal address and generate a false negative.

	/* blah blah blah */
	pa = PAGE_ALIGN(pa);
	return kvm_vcpu_is_legal_gpa(pa) &&
	       kvm_vcpu_is_legal_gpa(pa + size - 1);

> +}
> +
> +static bool nested_vmcb_check_controls(struct kvm_vcpu *vcpu,
> +				       struct vmcb_control_area *control)
>  {
>  	if ((vmcb_is_intercept(control, INTERCEPT_VMRUN)) == 0)
>  		return false;
> @@ -243,6 +251,13 @@ static bool nested_vmcb_check_controls(struct vmcb_control_area *control)
>  	    !npt_enabled)
>  		return false;
>  
> +	if (!nested_svm_check_bitmap_pa(vcpu, control->msrpm_base_pa,
> +	    MSRPM_ALLOC_SIZE))
> +		return false;
> +	if (!nested_svm_check_bitmap_pa(vcpu, control->iopm_base_pa,
> +	    IOPM_ALLOC_SIZE - PAGE_SIZE + 1))

Align with the function's paranthesis, not the if statements, for both.

	
	if (!nested_svm_check_bitmap_pa(vcpu, control->iopm_base_pa,
					IOPM_ALLOC_SIZE - PAGE_SIZE + 1))
> +		return false;
> +
>  	return true;
>  }
>  
> @@ -275,7 +290,7 @@ static bool nested_vmcb_check_save(struct vcpu_svm *svm, struct vmcb *vmcb12)
>  		    kvm_vcpu_is_illegal_gpa(vcpu, vmcb12->save.cr3))
>  			return false;
>  	}
> -	if (!kvm_is_valid_cr4(&svm->vcpu, vmcb12->save.cr4))
> +	if (!kvm_is_valid_cr4(vcpu, vmcb12->save.cr4))
>  		return false;
>  
>  	return true;
> @@ -531,7 +546,7 @@ int nested_svm_vmrun(struct vcpu_svm *svm)
>  	load_nested_vmcb_control(svm, &vmcb12->control);
>  
>  	if (!nested_vmcb_check_save(svm, vmcb12) ||
> -	    !nested_vmcb_check_controls(&svm->nested.ctl)) {
> +	    !nested_vmcb_check_controls(&svm->vcpu, &svm->nested.ctl)) {

Pass "vcpu" directly (probably only once you rebase).

>  		vmcb12->control.exit_code    = SVM_EXIT_ERR;
>  		vmcb12->control.exit_code_hi = 0;
>  		vmcb12->control.exit_info_1  = 0;
> @@ -1207,7 +1222,7 @@ static int svm_set_nested_state(struct kvm_vcpu *vcpu,
>  		goto out_free;
>  
>  	ret = -EINVAL;
> -	if (!nested_vmcb_check_controls(ctl))
> +	if (!nested_vmcb_check_controls(vcpu, ctl))
>  		goto out_free;
>  
>  	/*
> -- 
> 2.27.0
>