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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