KVM: Ensure all vcpus are consistent with in-kernel irqchip settings
 

From: Avi Kivity <avi@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@ellerman.id.au>
Signed-off-by: Avi Kivity <avi@redhat.com>
(backported from commit 3e515705a1f46beb1c942bb8043c16f8ac7b1e9e upstream)
Signed-off-by: Brad Figg <brad.figg@canonical.com>
Signed-off-by: Herton Ronaldo Krzesinski <herton.krzesinski@canonical.com>
---
arch/x86/kvm/x86.c | 9 +++++++++
.../binary-custom.d/openvz/src/arch/x86/kvm/x86.c | 9 +++++++++
.../openvz/src/include/linux/kvm_host.h | 2 ++
.../binary-custom.d/openvz/src/virt/kvm/kvm_main.c | 5 +++++
debian/binary-custom.d/xen/src/arch/x86/kvm/x86.c | 9 +++++++++
.../xen/src/include/linux/kvm_host.h | 2 ++
debian/binary-custom.d/xen/src/virt/kvm/kvm_main.c | 5 +++++
include/linux/kvm_host.h | 2 ++
virt/kvm/kvm_main.c | 5 +++++
9 files changed, 48 insertions(+)

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 9331b67..d6d7cfe 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -1582,6 +1582,9 @@ long kvm_arch_vm_ioctl(struct file *filp,
break;
}
case KVM_CREATE_IRQCHIP:
+ r = -EINVAL;
+ if (atomic_read(&kvm->online_vcpus))
+ goto out;
r = -ENOMEM;
kvm->arch.vpic = kvm_create_pic(kvm);
if (kvm->arch.vpic) {
@@ -3350,6 +3353,11 @@ 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;
@@ -3435,6 +3443,7 @@ static void kvm_free_vcpus(struct kvm *kvm)
}
}

+ atomic_set(&kvm->online_vcpus, 0);
}

void kvm_arch_destroy_vm(struct kvm *kvm)
diff --git a/debian/binary-custom.d/openvz/src/arch/x86/kvm/x86.c b/debian/binary-custom.d/openvz/src/arch/x86/kvm/x86.c
index 9331b67..d6d7cfe 100644
--- a/debian/binary-custom.d/openvz/src/arch/x86/kvm/x86.c
+++ b/debian/binary-custom.d/openvz/src/arch/x86/kvm/x86.c
@@ -1582,6 +1582,9 @@ long kvm_arch_vm_ioctl(struct file *filp,
break;
}
case KVM_CREATE_IRQCHIP:
+ r = -EINVAL;
+ if (atomic_read(&kvm->online_vcpus))
+ goto out;
r = -ENOMEM;
kvm->arch.vpic = kvm_create_pic(kvm);
if (kvm->arch.vpic) {
@@ -3350,6 +3353,11 @@ 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;
@@ -3435,6 +3443,7 @@ static void kvm_free_vcpus(struct kvm *kvm)
}
}

+ atomic_set(&kvm->online_vcpus, 0);
}

void kvm_arch_destroy_vm(struct kvm *kvm)
diff --git a/debian/binary-custom.d/openvz/src/include/linux/kvm_host.h b/debian/binary-custom.d/openvz/src/include/linux/kvm_host.h
index 588e4f9..95ec906 100644
--- a/debian/binary-custom.d/openvz/src/include/linux/kvm_host.h
+++ b/debian/binary-custom.d/openvz/src/include/linux/kvm_host.h
@@ -121,6 +121,7 @@ struct kvm {
struct kvm_memory_slot memslots[KVM_MEMORY_SLOTS +
KVM_PRIVATE_MEM_SLOTS];
struct kvm_vcpu *vcpus[KVM_MAX_VCPUS];
+ atomic_t online_vcpus;
struct list_head vm_list;
struct file *filp;
struct kvm_io_bus mmio_bus;
@@ -307,5 +308,6 @@ struct kvm_stats_debugfs_item {
struct dentry *dentry;
};
extern struct kvm_stats_debugfs_item debugfs_entries[];
+bool kvm_vcpu_compatible(struct kvm_vcpu *vcpu);

#endif
diff --git a/debian/binary-custom.d/openvz/src/virt/kvm/kvm_main.c b/debian/binary-custom.d/openvz/src/virt/kvm/kvm_main.c
index 07adef4..d9a8ae0 100644
--- a/debian/binary-custom.d/openvz/src/virt/kvm/kvm_main.c
+++ b/debian/binary-custom.d/openvz/src/virt/kvm/kvm_main.c
@@ -802,11 +802,16 @@ static int kvm_vm_ioctl_create_vcpu(struct kvm *kvm, int n)
return r;

mutex_lock(&kvm->lock);
+ if (!kvm_vcpu_compatible(vcpu)) {
+ r = -EINVAL;
+ goto vcpu_destroy;
+ }
if (kvm->vcpus[n]) {
r = -EEXIST;
goto vcpu_destroy;
}
kvm->vcpus[n] = vcpu;
+ atomic_inc(&kvm->online_vcpus);
mutex_unlock(&kvm->lock);

/* Now it's all set up, let userspace reach it */
diff --git a/debian/binary-custom.d/xen/src/arch/x86/kvm/x86.c b/debian/binary-custom.d/xen/src/arch/x86/kvm/x86.c
index 9331b67..d6d7cfe 100644
--- a/debian/binary-custom.d/xen/src/arch/x86/kvm/x86.c
+++ b/debian/binary-custom.d/xen/src/arch/x86/kvm/x86.c
@@ -1582,6 +1582,9 @@ long kvm_arch_vm_ioctl(struct file *filp,
break;
}
case KVM_CREATE_IRQCHIP:
+ r = -EINVAL;
+ if (atomic_read(&kvm->online_vcpus))
+ goto out;
r = -ENOMEM;
kvm->arch.vpic = kvm_create_pic(kvm);
if (kvm->arch.vpic) {
@@ -3350,6 +3353,11 @@ 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;
@@ -3435,6 +3443,7 @@ static void kvm_free_vcpus(struct kvm *kvm)
}
}

+ atomic_set(&kvm->online_vcpus, 0);
}

void kvm_arch_destroy_vm(struct kvm *kvm)
diff --git a/debian/binary-custom.d/xen/src/include/linux/kvm_host.h b/debian/binary-custom.d/xen/src/include/linux/kvm_host.h
index 588e4f9..95ec906 100644
--- a/debian/binary-custom.d/xen/src/include/linux/kvm_host.h
+++ b/debian/binary-custom.d/xen/src/include/linux/kvm_host.h
@@ -121,6 +121,7 @@ struct kvm {
struct kvm_memory_slot memslots[KVM_MEMORY_SLOTS +
KVM_PRIVATE_MEM_SLOTS];
struct kvm_vcpu *vcpus[KVM_MAX_VCPUS];
+ atomic_t online_vcpus;
struct list_head vm_list;
struct file *filp;
struct kvm_io_bus mmio_bus;
@@ -307,5 +308,6 @@ struct kvm_stats_debugfs_item {
struct dentry *dentry;
};
extern struct kvm_stats_debugfs_item debugfs_entries[];
+bool kvm_vcpu_compatible(struct kvm_vcpu *vcpu);

#endif
diff --git a/debian/binary-custom.d/xen/src/virt/kvm/kvm_main.c b/debian/binary-custom.d/xen/src/virt/kvm/kvm_main.c
index 07adef4..d9a8ae0 100644
--- a/debian/binary-custom.d/xen/src/virt/kvm/kvm_main.c
+++ b/debian/binary-custom.d/xen/src/virt/kvm/kvm_main.c
@@ -802,11 +802,16 @@ static int kvm_vm_ioctl_create_vcpu(struct kvm *kvm, int n)
return r;

mutex_lock(&kvm->lock);
+ if (!kvm_vcpu_compatible(vcpu)) {
+ r = -EINVAL;
+ goto vcpu_destroy;
+ }
if (kvm->vcpus[n]) {
r = -EEXIST;
goto vcpu_destroy;
}
kvm->vcpus[n] = vcpu;
+ atomic_inc(&kvm->online_vcpus);
mutex_unlock(&kvm->lock);

/* Now it's all set up, let userspace reach it */
diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
index 588e4f9..95ec906 100644
--- a/include/linux/kvm_host.h
+++ b/include/linux/kvm_host.h
@@ -121,6 +121,7 @@ struct kvm {
struct kvm_memory_slot memslots[KVM_MEMORY_SLOTS +
KVM_PRIVATE_MEM_SLOTS];
struct kvm_vcpu *vcpus[KVM_MAX_VCPUS];
+ atomic_t online_vcpus;
struct list_head vm_list;
struct file *filp;
struct kvm_io_bus mmio_bus;
@@ -307,5 +308,6 @@ struct kvm_stats_debugfs_item {
struct dentry *dentry;
};
extern struct kvm_stats_debugfs_item debugfs_entries[];
+bool kvm_vcpu_compatible(struct kvm_vcpu *vcpu);

#endif
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 07adef4..d9a8ae0 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -802,11 +802,16 @@ static int kvm_vm_ioctl_create_vcpu(struct kvm *kvm, int n)
return r;

mutex_lock(&kvm->lock);
+ if (!kvm_vcpu_compatible(vcpu)) {
+ r = -EINVAL;
+ goto vcpu_destroy;
+ }
if (kvm->vcpus[n]) {
r = -EEXIST;
goto vcpu_destroy;
}
kvm->vcpus[n] = vcpu;
+ atomic_inc(&kvm->online_vcpus);
mutex_unlock(&kvm->lock);

/* Now it's all set up, let userspace reach it */
--
1.7.9.5


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