KVM: Prevent kvm_init from corrupting debugfs structures

I'm seeing an oops condition when kvm-intel and kvm-amd are modprobe'd
during boot (say on an Intel system) and then rmmod'd:

   # modprobe kvm-intel
     kvm_init()
     kvm_init_debug()
     kvm_arch_init()  <-- stores debugfs dentries internally
     (success, etc)

   # modprobe kvm-amd
     kvm_init()
     kvm_init_debug() <-- second initialization clobbers kvm's
                          internal pointers to dentries
     kvm_arch_init()
     kvm_exit_debug() <-- and frees them

   # rmmod kvm-intel
     kvm_exit()
     kvm_exit_debug() <-- double free of debugfs files!

     *BOOM*

If execution gets to the end of kvm_init(), then the calling module has been
established as the kvm provider.  Move the debugfs initialization to the end of
the function, and remove the now-unnecessary call to kvm_exit_debug() from the
error path.  That way we avoid trampling on the debugfs entries and freeing
them twice.

Cc: stable@kernel.org
Signed-off-by: Darrick J. Wong <djwong@us.ibm.com>
Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>

diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index b7c78a4..7495ce3 100644 (file)
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -2717,8 +2717,6 @@ int kvm_init(void *opaque, unsigned int vcpu_size,
        int r;
        int cpu;
 
-       kvm_init_debug();
-
        r = kvm_arch_init(opaque);
        if (r)
                goto out_fail;
@@ -2785,6 +2783,8 @@ int kvm_init(void *opaque, unsigned int vcpu_size,
        kvm_preempt_ops.sched_in = kvm_sched_in;
        kvm_preempt_ops.sched_out = kvm_sched_out;
 
+       kvm_init_debug();
+
        return 0;
 
 out_free:
@@ -2807,7 +2807,6 @@ out_free_0:
 out:
        kvm_arch_exit();
 out_fail:
-       kvm_exit_debug();
        return r;
 }
 EXPORT_SYMBOL_GPL(kvm_init);
@@ -2815,6 +2814,7 @@ EXPORT_SYMBOL_GPL(kvm_init);
 void kvm_exit(void)
 {
        tracepoint_synchronize_unregister();
+       kvm_exit_debug();
        misc_deregister(&kvm_dev);
        kmem_cache_destroy(kvm_vcpu_cache);
        sysdev_unregister(&kvm_sysdev);
@@ -2824,7 +2824,6 @@ void kvm_exit(void)
        on_each_cpu(hardware_disable, NULL, 1);
        kvm_arch_hardware_unsetup();
        kvm_arch_exit();
-       kvm_exit_debug();
        free_cpumask_var(cpus_hardware_enabled);
        __free_page(bad_page);
 }