Re: [PATCH] KVM: X86: Dynamically allocating MSR number lists(msrs_to_save[], emulated_msrs[], msr_based_features[])

[Xiaoyao Li]

On 11/5/2019 6:41 PM, Paolo Bonzini wrote:
> On 05/11/19 10:20, Chenyi Qiang wrote:
> > The three msr number lists(msrs_to_save[], emulated_msrs[] and
> > msr_based_features[]) are global arrays of kvm.ko, which are
> > initialized/adjusted (copy supported MSRs forward to override the
> > unsupported MSRs) when installing kvm-{intel,amd}.ko, but it doesn't
> > reset these three arrays to their initial value when uninstalling
> > kvm-{intel,amd}.ko. Thus, at the next installation, kvm-{intel,amd}.ko
> > will initialize the modified arrays with some MSRs lost and some MSRs
> > duplicated.
> >
> > So allocate and initialize these three MSR number lists dynamically when
> > installing kvm-{intel,amd}.ko and free them when uninstalling.
>
> I don't understand.  Do you mean insmod/rmmod when you say
> installing/uninstalling? Global data must be reloaded from the ELF file
> when insmod is executed.

Yes, we mean insmod/rmmod.
The problem is that these three MSR arrays belong to kvm.ko but not 
kvm-{intel,amd}.ko. When we rmmod kvm_intel.ko, it does nothing to them.

> How is the bug reproducible?

Suppose there is an intel machine.

1. You can first run
	#rmmod kvm-intel.ko
	#insmod kvm-intel.ko nested=0
2. and then
	#rmmod kvm-intel.ko
	#insmod kvm-intel.ko nested=1

In step 1, all the vmx-related MSRs in msr_based_features[] are not 
supported due to nested=0. And it will move MSR_IA32_UCODE_REV and 
MSR_IA32_ARCH_CAPABILITIES (on my Cascadelake server) forward to 
override array member 0 and 1 (MSR_IA32_VMX_BASIC and 
MSR_IA32_VMX_TRUE_PINBASED_CTLS).

In step 2, we just lose MSR_IA32_VMX_BASIC and 
MSR_IA32_VMX_TRUE_PINBASED_CTLS of VMX and get duplicated 
MSR_IA32_UCODE_REV and MSR_IA32_ARCH_CAPABILITIES.

> Paolo