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Commit 0ea4ed8e authored by Darrick J. Wong's avatar Darrick J. Wong Committed by Marcelo Tosatti
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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: default avatarDarrick J. Wong <djwong@us.ibm.com>
Signed-off-by: default avatarMarcelo 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 @@ int kvm_init(void *opaque, unsigned int vcpu_size, 
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);

}