KVM: x86: Assertions to check no overrun in MSR lists

Currently there is no check whether shared MSRs list overrun the allocated size
which can results in bugs. In addition there is no check that vmx->guest_msrs
has sufficient space to accommodate all the VMX msrs.  This patch adds the
assertions.
Signed-off-by: Nadav Amit <namit@cs.technion.ac.il>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

arch/x86/kvm/vmx.c

@@ -7608,6 +7608,8 @@ static struct kvm_vcpu *vmx_create_vcpu(struct kvm *kvm, unsigned int id)
 		goto free_vcpu;
 
 	vmx->guest_msrs = kmalloc(PAGE_SIZE, GFP_KERNEL);
+	BUILD_BUG_ON(PAGE_SIZE / sizeof(struct shared_msr_entry) < NR_VMX_MSR);
+
 	err = -ENOMEM;
 	if (!vmx->guest_msrs) {
 		goto uninit_vcpu;

arch/x86/kvm/x86.c

@@ -212,6 +212,7 @@ static void shared_msr_update(unsigned slot, u32 msr)
 
 void kvm_define_shared_msr(unsigned slot, u32 msr)
 {
+	BUG_ON(slot >= KVM_NR_SHARED_MSRS);
 	if (slot >= shared_msrs_global.nr)
 		shared_msrs_global.nr = slot + 1;
 	shared_msrs_global.msrs[slot] = msr;