Paolo Bonzini <pbonzini@xxxxxxxxxx> writes:
> On 04/06/20 12:53, Vitaly Kuznetsov wrote:
>> Exception we're trying to inject comes from
>>
>> nested_vmx_get_vmptr()
>> kvm_read_guest_virt()
>> kvm_read_guest_virt_helper()
>> vcpu->arch.walk_mmu->gva_to_gpa()
>>
>> but it seems it is only set if GVA to GPA convertion fails. In case it
>> doesn't, we can still fail kvm_vcpu_read_guest_page() and return
>> X86EMUL_IO_NEEDED but nested_vmx_get_vmptr() doesn't case what we return
>> and does kvm_inject_emulated_page_fault(). This can happen when VMXON
>> parameter is MMIO, for example.
>>
>> How do fix this? We can either properly exit to userspace for handling
>> or, if we decide that handling such requests makes little sense, just
>> inject #GP if exception is not set, e.g.
>>
>> diff --git a/arch/x86/kvm/vmx/nested.c b/arch/x86/kvm/vmx/nested.c
>> index 9c74a732b08d..a21e2f32f59b 100644
>> --- a/arch/x86/kvm/vmx/nested.c
>> +++ b/arch/x86/kvm/vmx/nested.c
>> @@ -4635,7 +4635,11 @@ static int nested_vmx_get_vmptr(struct kvm_vcpu *vcpu, gpa_t *vmpointer)
>> return 1;
>>
>> if (kvm_read_guest_virt(vcpu, gva, vmpointer, sizeof(*vmpointer), &e)) {
>> - kvm_inject_emulated_page_fault(vcpu, &e);
>> + if (e.vector == PF_VECTOR)
>> + kvm_inject_emulated_page_fault(vcpu, &e);
>> + else
>> + kvm_inject_gp(vcpu, 0);
>> +
>> return 1;
>> }
>>
>
> Yes, this is a plausible fix (with a comment explaining that we are
> taking a shortcut). Perhaps a better check would be
>
> r = kvm_read_guest_virt(vcpu, gva, vmpointer, sizeof(*vmpointer), &e);
> if (r != X86EMUL_CONTINUE) {
> if (r == X86EMUL_PROPAGATE_FAULT) {
> kvm_inject_emulated_page_fault(vcpu, &e);
> } else {
> /* ... */
> kvm_inject_gp(vcpu, 0);
> }
> return 1;
> }
>
> Are you going to send a patch?
>
Sure, will do.
--
Vitaly
