Re: [PATCH 1/3 v2] nSVM: Check addresses of MSR and IO bitmap

[Krish Sadhukhan <krish.sadhukhan@oracle.com>]

On 1/19/21 4:45 PM, Sean Christopherson wrote:
> On Sat, Jan 16, 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."
>>
>> Also check that these addresses are aligned on page boundary.
>>
>> Signed-off-by: Krish Sadhukhan <krish.sadhukhan@oracle.com>
>> ---
>>   arch/x86/kvm/svm/nested.c | 18 ++++++++++++------
>>   1 file changed, 12 insertions(+), 6 deletions(-)
>>
>> diff --git a/arch/x86/kvm/svm/nested.c b/arch/x86/kvm/svm/nested.c
>> index cb4c6ee10029..2419f392a13d 100644
>> --- a/arch/x86/kvm/svm/nested.c
>> +++ b/arch/x86/kvm/svm/nested.c
>> @@ -211,7 +211,8 @@ 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_vmcb_check_controls(struct kvm_vcpu *vcpu,
>> +				       struct vmcb_control_area *control)
>>   {
>>   	if ((vmcb_is_intercept(control, INTERCEPT_VMRUN)) == 0)
>>   		return false;
>> @@ -223,10 +224,15 @@ static bool nested_vmcb_check_controls(struct vmcb_control_area *control)
>>   	    !npt_enabled)
>>   		return false;
>>   
>> +	if (!page_address_valid(vcpu, control->msrpm_base_pa))
>> +		return false;
>> +	if (!page_address_valid(vcpu, control->iopm_base_pa))
> These checks are wrong.  The MSRPM is 8kb in size, and the IOPM is 12kb, and the
> APM explicitly states that the last byte is checked:
>
>    if the address of the last byte in the table is greater than or equal to the
>    maximum supported physical address, this is treated as illegal VMCB state and
>    causes a #VMEXIT(VMEXIT_INVALID).
>
> KVM can't check just the last byte, as that would fail to detect a wrap of the
> 64-bit boundary.  Might be worth adding yet another helper?  I think this will
> work, though I'm sure Paolo has a much more clever solution :-)
>
>    static inline bool page_range_valid(struct kvm_vcpu *vcpu, gpa_t gpa, int size)
>    {
> 	gpa_t last_page = gpa + size - PAGE_SIZE;
>
> 	if (last_page < gpa)
> 		return false;
>
> 	return page_address_valid(last_page);
>    }
>
> Note, the IOPM is 12kb in size, but KVM allocates and initializes 16kb, i.e.
> using IOPM_ALLOC_ORDER for the check would be wrong.  Maybe define the actual
> size for both bitmaps and use get_order() instead of hardcoding the order?  That
> would make it easy to "fix" svm_hardware_setup() so that it doesn't initialize
> unused memory.


Is there any issues with using alloc_pages_exact() instead of 
alloc_pages() for allocating the IOPM bitmap ?

>
>> +		return false;
>> +
>>   	return true;
>>   }
>>   
>> -static bool nested_vmcb_checks(struct vcpu_svm *svm, struct vmcb *vmcb12)
>> +static bool nested_vmcb_checks(struct kvm_vcpu *vcpu, struct vmcb *vmcb12)
>>   {
>>   	bool vmcb12_lma;
>>   
>> @@ -255,10 +261,10 @@ static bool nested_vmcb_checks(struct vcpu_svm *svm, struct vmcb *vmcb12)
>>   		    (vmcb12->save.cr3 & MSR_CR3_LONG_MBZ_MASK))
>>   			return false;
>>   	}
>> -	if (!kvm_is_valid_cr4(&svm->vcpu, vmcb12->save.cr4))
>> +	if (!kvm_is_valid_cr4(vcpu, vmcb12->save.cr4))
>>   		return false;
>>   
>> -	return nested_vmcb_check_controls(&vmcb12->control);
>> +	return nested_vmcb_check_controls(vcpu, &vmcb12->control);
>>   }
>>   
>>   static void load_nested_vmcb_control(struct vcpu_svm *svm,
>> @@ -485,7 +491,7 @@ int nested_svm_vmrun(struct vcpu_svm *svm)
>>   	if (WARN_ON_ONCE(!svm->nested.initialized))
>>   		return -EINVAL;
>>   
>> -	if (!nested_vmcb_checks(svm, vmcb12)) {
>> +	if (!nested_vmcb_checks(&svm->vcpu, vmcb12)) {
>>   		vmcb12->control.exit_code    = SVM_EXIT_ERR;
>>   		vmcb12->control.exit_code_hi = 0;
>>   		vmcb12->control.exit_info_1  = 0;
>> @@ -1173,7 +1179,7 @@ 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
>>