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Date: Tue, 15 Nov 2016 09:23:08 -0800
From: Kees Cook <keescook@...omium.org>
To: "kernel-hardening@...ts.openwall.com" <kernel-hardening@...ts.openwall.com>
Cc: Peter Zijlstra <peterz@...radead.org>, Will Deacon <will.deacon@....com>,
Greg KH <gregkh@...uxfoundation.org>, David Windsor <dave@...gbits.org>,
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 Tue, Nov 15, 2016 at 8:50 AM, Rik van Riel <riel@...hat.com> wrote:
> On Mon, 2016-11-14 at 12:31 -0800, Kees Cook wrote:
>> On Fri, Nov 11, 2016 at 12:17 PM, Peter Zijlstra <peterz@...radead.or
>> g> wrote:
>> >
>> > On Fri, Nov 11, 2016 at 10:04:42AM -0800, Kees Cook wrote:
>> >
>> > >
>> > > I'm totally open about how to get there, but things can't just be
>> > > opt-in.
>> > There really is no alternative.
>> I realize you feel that way, but if we can find a way to squeeze
>> mistakes down to impossible or very small, that has a strong effect
>> on
>> the future of avoiding exploitation of these kinds of things.
>>
>> >
>> > refcount_t; should only have: inc, inc_not_zero, dec_and_test
>> Sounds good. Two questions remain:
>>
>> - how to deal with existing refcounting atomic_t users that want _add
>> and _sub?
>> - keeping this fast enough that it can be used even in very sensitive
>> places (net, fs, etc).
>>
>> >
>> > stats_t; should only have: add,sub
>> Seems right, though why not inc/dec? And shouldn't it have a _read of
>> some kind?
>>
>> Keeping the implementation details of refcount_t and stats_t opaque
>> to
>> the users should discourage misuse...
>
> I suspect a lack of inc_not_zero and dec_and_test would
> be the biggest things discouraging misuse of stats_t
> for reference counting :)
Right, but it's the continuing atomic_t use that concerns me...
-Kees
--
Kees Cook
Nexus Security
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