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Date: Sat, 29 Oct 2016 01:05:29 -0400
From: David Windsor <>
	"Reshetova, Elena" <>, Hans Liljestrand <>, 
	Kees Cook <>, AKASHI Takahiro <>, 
	Colin Vidal <>
Subject: Expanding HARDENED_ATOMIC


I've created a branch on Elena's github repo called
which incorporates the PAX_REFCOUNT changes to extend atomic_t
coverage to kernel reference counters that were originally integer
types.  Our work to this point only addresses existing atomic_t users:
this patch is a first attempt to convert non-atomic_t reference
counter users to use atomic_t, and thus get overflow protection.

The users addressed in this branch are:
  * struct fs_struct.users
  * struct tty_port.count
  * struct tty_ldisc_ops.refcount
  * struct pipe_inode_info.{readers|writers|files|waiting_writers}
  * struct kmem_cache.refcount

This branch currently does not compile, as I am in the process of
cherrypicking the necessary changes from PAX_REFCOUNT.

I wanted to let Elena/Hans know about this now, as they are preparing
the next RFC.  I don't know if we want to actually expand kernel
coverage in this round of RFC's, but there shouldn't be much more work
left to get this working.


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