From: David Matlack dmatlack@google.com
commit 5f6de5cbebee925a612856fce6f9182bb3eee0db upstream.
Tie the lifetime the KVM module to the lifetime of each VM via kvm.users_count. This way anything that grabs a reference to the VM via kvm_get_kvm() cannot accidentally outlive the KVM module.
Prior to this commit, the lifetime of the KVM module was tied to the lifetime of /dev/kvm file descriptors, VM file descriptors, and vCPU file descriptors by their respective file_operations "owner" field. This approach is insufficient because references grabbed via kvm_get_kvm() do not prevent closing any of the aforementioned file descriptors.
This fixes a long standing theoretical bug in KVM that at least affects async page faults. kvm_setup_async_pf() grabs a reference via kvm_get_kvm(), and drops it in an asynchronous work callback. Nothing prevents the VM file descriptor from being closed and the KVM module from being unloaded before this callback runs.
Fixes: af585b921e5d ("KVM: Halt vcpu if page it tries to access is swapped out") Fixes: 3d3aab1b973b ("KVM: set owner of cpu and vm file operations") Cc: stable@vger.kernel.org Suggested-by: Ben Gardon bgardon@google.com [ Based on a patch from Ben implemented for Google's kernel. ] Signed-off-by: David Matlack dmatlack@google.com Message-Id: 20220303183328.1499189-2-dmatlack@google.com Signed-off-by: Paolo Bonzini pbonzini@redhat.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- virt/kvm/kvm_main.c | 13 +++++++++++++ 1 file changed, 13 insertions(+)
--- a/virt/kvm/kvm_main.c +++ b/virt/kvm/kvm_main.c @@ -115,6 +115,8 @@ EXPORT_SYMBOL_GPL(kvm_debugfs_dir); static int kvm_debugfs_num_entries; static const struct file_operations *stat_fops_per_vm[];
+static struct file_operations kvm_chardev_ops; + static long kvm_vcpu_ioctl(struct file *file, unsigned int ioctl, unsigned long arg); #ifdef CONFIG_KVM_COMPAT @@ -766,6 +768,16 @@ static struct kvm *kvm_create_vm(unsigne
preempt_notifier_inc();
+ /* + * When the fd passed to this ioctl() is opened it pins the module, + * but try_module_get() also prevents getting a reference if the module + * is in MODULE_STATE_GOING (e.g. if someone ran "rmmod --wait"). + */ + if (!try_module_get(kvm_chardev_ops.owner)) { + r = -ENODEV; + goto out_err; + } + return kvm;
out_err: @@ -844,6 +856,7 @@ static void kvm_destroy_vm(struct kvm *k preempt_notifier_dec(); hardware_disable_all(); mmdrop(mm); + module_put(kvm_chardev_ops.owner); }
void kvm_get_kvm(struct kvm *kvm)