Re: [PATCH v2] kasan: remove kasan_find_vm_area() to prevent possible deadlock

[Yeo Reum Yun]

Hi ByungChul,

[...]
> I checked the critical section by &vn->busy.lock in find_vm_area().  The
> time complextity looks O(log N).  I don't think an irq disabled section
> of O(log N) is harmful.  I still think using
> spin_lock_irqsave(&vn->busy.lock) can resolve this issue with no worry
> of significant irq delay.  Am I missing something?

I don't agree for this. 
since in PREEMPT_RT case, it has the same problem.

In case of PREEMPT_RT, spin_lock_irqsave() becomes rt_spin_lock() which is sleepable.
But, KASAN calls "rt_spin_lock()" holding raw_spin_lock_irqsave() which is definitely wrong.

But as Uladzislau said, without reference count manage, UAF can always happen.
IOW, If KASAN to dump vm information, I think we need:
    1. manage reference for vmap_area.
    2. find_vm_area() with rcu version.


Thanks.

--  
Sincerely,
Yeoreum Yun