[PATCH 1/1] [CVE-2012-1601] [PRECISE] KVM: Ensure all vcpus are consistent with in-kernel irqchip settings

[Brad Figg]

From: Avi Kivity <avi at redhat.com>

CVE-2012-1601

BugLink: http://bugs.launchpad.net/bugs/971685

If some vcpus are created before KVM_CREATE_IRQCHIP, then
irqchip_in_kernel() and vcpu->arch.apic will be inconsistent, leading
to potential NULL pointer dereferences.

Fix by:
- ensuring that no vcpus are installed when KVM_CREATE_IRQCHIP is called
- ensuring that a vcpu has an apic if it is installed after KVM_CREATE_IRQCHIP

This is somewhat long winded because vcpu->arch.apic is created without
kvm->lock held.

Based on earlier patch by Michael Ellerman.

Signed-off-by: Michael Ellerman <michael at ellerman.id.au>
Signed-off-by: Avi Kivity <avi at redhat.com>
(cherry picked from commit 3e515705a1f46beb1c942bb8043c16f8ac7b1e9e)
Signed-off-by: Brad Figg <brad.figg at canonical.com>
---
 arch/ia64/kvm/kvm-ia64.c |    5 +++++
 arch/x86/kvm/x86.c       |    8 ++++++++
 include/linux/kvm_host.h |    7 +++++++
 virt/kvm/kvm_main.c      |    4 ++++
 4 files changed, 24 insertions(+)

diff --git a/arch/ia64/kvm/kvm-ia64.c b/arch/ia64/kvm/kvm-ia64.c
index 43f4c92..7073185 100644
--- a/arch/ia64/kvm/kvm-ia64.c
+++ b/arch/ia64/kvm/kvm-ia64.c
@@ -1169,6 +1169,11 @@ out:
 
 #define PALE_RESET_ENTRY    0x80000000ffffffb0UL
 
+bool kvm_vcpu_compatible(struct kvm_vcpu *vcpu)
+{
+	return irqchip_in_kernel(vcpu->kcm) == (vcpu->arch.apic != NULL);
+}
+
 int kvm_arch_vcpu_init(struct kvm_vcpu *vcpu)
 {
 	struct kvm_vcpu *v;
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 778018b..759af84 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -3070,6 +3070,9 @@ long kvm_arch_vm_ioctl(struct file *filp,
 		r = -EEXIST;
 		if (kvm->arch.vpic)
 			goto create_irqchip_unlock;
+		r = -EINVAL;
+		if (atomic_read(&kvm->online_vcpus))
+			goto create_irqchip_unlock;
 		r = -ENOMEM;
 		vpic = kvm_create_pic(kvm);
 		if (vpic) {
@@ -5858,6 +5861,11 @@ void kvm_arch_check_processor_compat(void *rtn)
 	kvm_x86_ops->check_processor_compatibility(rtn);
 }
 
+bool kvm_vcpu_compatible(struct kvm_vcpu *vcpu)
+{
+	return irqchip_in_kernel(vcpu->kvm) == (vcpu->arch.apic != NULL);
+}
+
 int kvm_arch_vcpu_init(struct kvm_vcpu *vcpu)
 {
 	struct page *page;
diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
index d526231..7e8a29f 100644
--- a/include/linux/kvm_host.h
+++ b/include/linux/kvm_host.h
@@ -738,6 +738,13 @@ static inline bool kvm_vcpu_is_bsp(struct kvm_vcpu *vcpu)
 {
 	return vcpu->kvm->bsp_vcpu_id == vcpu->vcpu_id;
 }
+
+bool kvm_vcpu_compatible(struct kvm_vcpu *vcpu);
+
+#else
+
+static inline bool kvm_vcpu_compatible(struct kvm_vcpu *vcpu) { return true; }
+
 #endif
 
 #ifdef __KVM_HAVE_DEVICE_ASSIGNMENT
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index d9cfb78..5007b7d 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -1665,6 +1665,10 @@ static int kvm_vm_ioctl_create_vcpu(struct kvm *kvm, u32 id)
 		goto vcpu_destroy;
 
 	mutex_lock(&kvm->lock);
+	if (!kvm_vcpu_compatible(vcpu)) {
+		r = -EINVAL;
+		goto unlock_vcpu_destroy;
+	}
 	if (atomic_read(&kvm->online_vcpus) == KVM_MAX_VCPUS) {
 		r = -EINVAL;
 		goto unlock_vcpu_destroy;
-- 
1.7.9.5