KVM: Disallow fork() and similar games when using a VM

We don't want the meaning of guest userspace changing under our feet.

Signed-off-by: Avi Kivity <avi@qumranet.com>

3 files changed, 11 insertions, 0 deletions

diff --git a/drivers/kvm/kvm.h b/drivers/kvm/kvm.h
index 1fd8158ced89..be18620bd656 100644
--- a/drivers/kvm/kvm.h
+++ b/drivers/kvm/kvm.h
@@ -305,6 +305,7 @@ struct kvm_vm_stat {
 
 struct kvm {
         struct mutex lock; /* protects everything except vcpus */
+        struct mm_struct *mm; /* userspace tied to this vm */
         int naliases;
         struct kvm_mem_alias aliases[KVM_ALIAS_SLOTS];
         int nmemslots;
diff --git a/drivers/kvm/kvm_main.c b/drivers/kvm/kvm_main.c
index aec6b67cfebb..0efd759e585f 100644
--- a/drivers/kvm/kvm_main.c
+++ b/drivers/kvm/kvm_main.c
@@ -165,6 +165,8 @@ static struct kvm *kvm_create_vm(void)
         if (IS_ERR(kvm))
                 goto out;
 
+        kvm->mm = current->mm;
+        atomic_inc(&kvm->mm->mm_count);
         kvm_io_bus_init(&kvm->pio_bus);
         mutex_init(&kvm->lock);
         kvm_io_bus_init(&kvm->mmio_bus);
@@ -202,12 +204,15 @@ void kvm_free_physmem(struct kvm *kvm)
 
 static void kvm_destroy_vm(struct kvm *kvm)
 {
+        struct mm_struct *mm = kvm->mm;
+
         spin_lock(&kvm_lock);
         list_del(&kvm->vm_list);
         spin_unlock(&kvm_lock);
         kvm_io_bus_destroy(&kvm->pio_bus);
         kvm_io_bus_destroy(&kvm->mmio_bus);
         kvm_arch_destroy_vm(kvm);
+        mmdrop(mm);
 }
 
 static int kvm_vm_release(struct inode *inode, struct file *filp)
@@ -818,6 +823,8 @@ static long kvm_vcpu_ioctl(struct file *filp,
         void __user *argp = (void __user *)arg;
         int r;
 
+        if (vcpu->kvm->mm != current->mm)
+                return -EIO;
         switch (ioctl) {
         case KVM_RUN:
                 r = -EINVAL;
@@ -976,6 +983,8 @@ static long kvm_vm_ioctl(struct file *filp,
         void __user *argp = (void __user *)arg;
         int r;
 
+        if (kvm->mm != current->mm)
+                return -EIO;
         switch (ioctl) {
         case KVM_CREATE_VCPU:
                 r = kvm_vm_ioctl_create_vcpu(kvm, arg);
diff --git a/kernel/fork.c b/kernel/fork.c
index 314f5101d2b0..05e0b6f4365b 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -393,6 +393,7 @@ void fastcall __mmdrop(struct mm_struct *mm)
         destroy_context(mm);
         free_mm(mm);
 }
+EXPORT_SYMBOL_GPL(__mmdrop);
 
 /*
  * Decrement the use count and release all resources for an mm.