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Date: Mon, 21 Nov 2016 12:13:13 -0800
From: "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To: Kees Cook <keescook@...omium.org>
Cc: Elena Reshetova <elena.reshetova@...el.com>,
"kernel-hardening@...ts.openwall.com" <kernel-hardening@...ts.openwall.com>,
Arnd Bergmann <arnd@...db.de>, Thomas Gleixner <tglx@...utronix.de>,
Ingo Molnar <mingo@...hat.com>,
"H. Peter Anvin" <h.peter.anvin@...el.com>,
Peter Zijlstra <peterz@...radead.org>,
Will Deacon <will.deacon@....com>, David Windsor <dwindsor@...il.com>,
Hans Liljestrand <ishkamiel@...il.com>
Subject: Re: [RFC v4 PATCH 03/13] kernel: identify wrapping atomic usage
On Sat, Nov 19, 2016 at 01:39:58PM -0800, Kees Cook wrote:
> On Sat, Nov 19, 2016 at 5:28 AM, Paul E. McKenney
> <paulmck@...ux.vnet.ibm.com> wrote:
> > On Thu, Nov 10, 2016 at 10:24:38PM +0200, Elena Reshetova wrote:
> >> From: David Windsor <dwindsor@...il.com>
> >>
> >> In some cases atomic is not used for reference
> >> counting and therefore should be allowed to overflow.
> >> Identify such cases and make a switch to non-hardened
> >> atomic version.
> >>
> >> The copyright for the original PAX_REFCOUNT code:
> >> - all REFCOUNT code in general: PaX Team <pageexec@...email.hu>
> >> - various false positive fixes: Mathias Krause <minipli@...glemail.com>
> >>
> >> Signed-off-by: Hans Liljestrand <ishkamiel@...il.com>
> >> Signed-off-by: Elena Reshetova <elena.reshetova@...el.com>
> >> Signed-off-by: David Windsor <dwindsor@...il.com>
> >
> > Not a fan of the rename from atomic_t to atomic_wrap_t.
>
> Yeah, the thread has grown considerably now. :) We're most likely
> looking at carving off two of the common atomic_t usage patterns into
> "stats_t" (with _add(), _sub(), and _read()), and "refcount_t" (with
> _inc(), _inc_not_zero(), _dec_and_test(), and _read(), along with a
> trap on overflow). With these in place, refcounts will be protected to
> avoid use-after-free exploits, things that don't care about wrapping
> will be annotated without a risk of them being turned into refcounts,
> and the remaining atomic_t uses will be easier to audit for misuse.
Whew!!! ;-)
Thanx, Paul
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