Re: [PATCH] kvm: Prevent kvm_init from corrupting debugfs structures

[Avi Kivity]

On 10/15/2009 08:21 AM, Darrick J. Wong wrote:

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.

   


Looks good.

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I have a truly marvellous patch that fixes the bug which this
signature is too narrow to contain.

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Re: [PATCH] kvm: Prevent kvm_init from corrupting debugfs structures

[Marcelo Tosatti]

On Wed, Oct 14, 2009 at 04:21:00PM -0700, Darrick J. Wong wrote:
 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.
 
 Signed-off-by: Darrick J. Wong djw...@us.ibm.com

Applied, thanks.

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[PATCH] kvm: Prevent kvm_init from corrupting debugfs structures

[Darrick J. Wong]

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.

Signed-off-by: Darrick J. Wong djw...@us.ibm.com
---

 virt/kvm/kvm_main.c |7 +++
 1 files changed, 3 insertions(+), 4 deletions(-)


diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index b7c78a4..7495ce3 100644
--- 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);
 }
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