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Message-ID: <20161111174630.GO3117@twins.programming.kicks-ass.net>
Date: Fri, 11 Nov 2016 18:46:30 +0100
From: Peter Zijlstra <peterz@...radead.org>
To: Kees Cook <keescook@...omium.org>
Cc: Will Deacon <will.deacon@....com>, Greg KH <gregkh@...uxfoundation.org>,
David Windsor <dave@...gbits.org>,
"kernel-hardening@...ts.openwall.com" <kernel-hardening@...ts.openwall.com>,
Elena Reshetova <elena.reshetova@...el.com>,
Arnd Bergmann <arnd@...db.de>, Thomas Gleixner <tglx@...utronix.de>,
Ingo Molnar <mingo@...hat.com>,
"H. Peter Anvin" <h.peter.anvin@...el.com>
Subject: Re: Re: [RFC v4 PATCH 00/13] HARDENED_ATOMIC
On Fri, Nov 11, 2016 at 09:43:00AM -0800, Kees Cook wrote:
> > 1) kref: Used for honest-to-goodness reference counters that want
> > overflow protection. Uses a new type: atomic_nowrap_t that has
> > HARDENED_ATOMIC protection.
>
> Based on other feedback, it sounds like we're better off with
> refcount_t (which kref could be implemented on top of). And refcount_t
> would have a limited API: inc, dec_and_test (or whatever is determined
> as sanely minimal).
>
> > 2) statistical counters: Atomic in all cases, but wraps.
>
> Yup. sequence_t seems to make the most sense on naming, I think. If we
> want to get crazy, the type could be sequence_wrap_t.
Why? atomic_t is still perfectly fine here, right?
> > 3) atomic_t: All other users of atomics (locks, etc.). Wrapping
> > behavior depends on a CONFIG setting.
>
> Correct: if CONFIG_PARANOID_ATOMIC (or something) is set, atomic_t is
> implemented as refcount_t, otherwise as sequence_t.
Can't happen. There is far more atomic_t usage than reference and/or
statistics counters.
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