Commit 0ea4ed8e authored Oct 14, 2009 by Darrick J. Wong Committed by Marcelo Tosatti Oct 16, 2009

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>

parent 8a8365c5

virt/kvm/kvm_main.c

+3 −4

Original line number	Diff line number	Diff line
		@@ -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);
		}

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