KVM: x86: hyperv: enforce vp_index < KVM_MAX_VCPUS

Hyper-V TLFS (5.0b) states:

> Virtual processors are identified by using an index (VP index). The
> maximum number of virtual processors per partition supported by the
> current implementation of the hypervisor can be obtained through CPUID
> leaf 0x40000005. A virtual processor index must be less than the
> maximum number of virtual processors per partition.

Forbid userspace to set VP_INDEX above KVM_MAX_VCPUS. get_vcpu_by_vpidx()
can now be optimized to bail early when supplied vpidx is >= KVM_MAX_VCPUS.

Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
Reviewed-by: Roman Kagan <rkagan@virtuozzo.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

diff --git a/arch/x86/kvm/hyperv.c b/arch/x86/kvm/hyperv.c
index 01d209a..0cd597b 100644 (file)
--- a/arch/x86/kvm/hyperv.c
+++ b/arch/x86/kvm/hyperv.c
@@ -132,8 +132,10 @@ static struct kvm_vcpu *get_vcpu_by_vpidx(struct kvm *kvm, u32 vpidx)
        struct kvm_vcpu *vcpu = NULL;
        int i;
 
-       if (vpidx < KVM_MAX_VCPUS)
-               vcpu = kvm_get_vcpu(kvm, vpidx);
+       if (vpidx >= KVM_MAX_VCPUS)
+               return NULL;
+
+       vcpu = kvm_get_vcpu(kvm, vpidx);
        if (vcpu && vcpu_to_hv_vcpu(vcpu)->vp_index == vpidx)
                return vcpu;
        kvm_for_each_vcpu(i, vcpu, kvm)
@@ -1044,7 +1046,7 @@ static int kvm_hv_set_msr(struct kvm_vcpu *vcpu, u32 msr, u64 data, bool host)
 
        switch (msr) {
        case HV_X64_MSR_VP_INDEX:
-               if (!host)
+               if (!host || (u32)data >= KVM_MAX_VCPUS)
                        return 1;
                hv->vp_index = (u32)data;
                break;