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Message-ID: <20170529083903.GA17735@infradead.org>
Date: Mon, 29 May 2017 01:39:04 -0700
From: Christoph Hellwig <hch@...radead.org>
To: Kees Cook <keescook@...omium.org>
Cc: Andrew Morton <akpm@...ux-foundation.org>,
Elena Reshetova <elena.reshetova@...el.com>,
Peter Zijlstra <peterz@...radead.org>,
Greg KH <gregkh@...uxfoundation.org>,
"Eric W. Biederman" <ebiederm@...ssion.com>,
Ingo Molnar <mingo@...hat.com>,
Alexey Dobriyan <adobriyan@...il.com>,
"Serge E. Hallyn" <serge@...lyn.com>, arozansk@...hat.com,
Davidlohr Bueso <dave@...olabs.net>,
Manfred Spraul <manfred@...orfullife.com>,
Christoph Hellwig <hch@...radead.org>,
"axboe@...nel.dk" <axboe@...nel.dk>,
James Bottomley <James.Bottomley@...senpartnership.com>,
"x86@...nel.org" <x86@...nel.org>, Ingo Molnar <mingo@...nel.org>,
Arnd Bergmann <arnd@...db.de>,
"David S. Miller" <davem@...emloft.net>,
Rik van Riel <riel@...hat.com>,
linux-arch <linux-arch@...r.kernel.org>,
"kernel-hardening@...ts.openwall.com" <kernel-hardening@...ts.openwall.com>,
LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 0/3] ipc subsystem refcounter conversions
On Sat, May 27, 2017 at 12:58:14PM -0700, Kees Cook wrote:
> FAST_REFCOUNT=n: use function-based refcount_t with cmpxvhg and
> full-verification
> FAST_REFCOUNT=y without arch-specific implementation: use atomic_t
> with no verification (i.e. no functional change from now)
> FAST_REFCOUNT=y with arch-specific implementation: use atomic_t with
> overflow protection
>
> which means FAST_REFCOUNT would need to be default-on so that mm,
> block, net users will remain happy.
>
> Does that sound reasonable?
I'd rather turn the options around so that the atomic_t or fast
arch implementations are the defaul. But either way it needs to
be configurable. Once that is done we can spread refcount_t everywhere
and everyone will be better off, if only for the documentation value
of the type when they use the atomic_t based implementation.
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