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Subject[PATCH v4 RESEND 1/5] KVM: x86: hyperv: enforce vp_index < KVM_MAX_VCPUS
Date
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>
---
arch/x86/kvm/hyperv.c | 8 +++++---
1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/arch/x86/kvm/hyperv.c b/arch/x86/kvm/hyperv.c
index 01d209ab5481..0cd597b0f754 100644
--- 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;
--
2.14.4
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