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Date: Thu, 1 Dec 2016 15:20:29 -0800
From: Kees Cook <keescook@...omium.org>
To: Peter Zijlstra <peterz@...radead.org>
Cc: David Windsor <dwindsor@...il.com>, "Reshetova, Elena" <elena.reshetova@...el.com>,
"kernel-hardening@...ts.openwall.com" <kernel-hardening@...ts.openwall.com>, Greg KH <gregkh@...uxfoundation.org>,
"will.deacon@....com" <will.deacon@....com>, Boqun Feng <boqun.feng@...il.com>,
Hans Liljestrand <ishkamiel@...il.com>, "aik@...abs.ru" <aik@...abs.ru>,
"david@...son.dropbear.id.au" <david@...son.dropbear.id.au>
Subject: Re: Conversion from atomic_t to refcount_t: summary of issues
On Thu, Dec 1, 2016 at 3:03 PM, Peter Zijlstra <peterz@...radead.org> wrote:
> On Thu, Dec 01, 2016 at 04:31:16PM -0500, David Windsor wrote:
>> Also, I'd like to point out that while identifying stats_t instances, I
>> have found a similar distribution of non-standard functions (as agreed upon
>> for the stats_t API).
>
>> First, usage of atomic_long_wrap_t (there currently isn't a stats_long_t
>> planned for implementation):
>
> There isn't even a stats_t planned. I'm still very much not convinced
> stats_t is needed or even makes sense.
>
> It wouldn't have any different semantics from atomic_t, and the only
> argument Kees made was that reduced atomic_t usage would make it easier
> to spot refcounts, but you're already building tools to find those.
>
> Once the tools work, who cares.
The tool is only part of the whole thing. By distinctly splitting the
other major atomic_t usage pattern away from atomic_t, it solidifies a
stats_t as NOT a reference counter. It's the slow feature-creep or bad
example situations that I'd like to avoid. Also, tools won't catch
everything, and doing manual inspection is much easier if we know a
stats_t cannot be misused.
There doesn't seem to be a good reason NOT to have stats_t, beyond the
work needed to create it and audit the places it should be used.
-Kees
--
Kees Cook
Nexus Security
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