From: Peter Zijlstra <peterz@infradead.org>
To: Kees Cook <keescook@chromium.org>
Cc: linux-kernel@vger.kernel.org, Eric Biggers <ebiggers3@gmail.com>,
Christoph Hellwig <hch@infradead.org>,
"axboe@kernel.dk" <axboe@kernel.dk>,
James Bottomley <James.Bottomley@hansenpartnership.com>,
Elena Reshetova <elena.reshetova@intel.com>,
Hans Liljestrand <ishkamiel@gmail.com>,
David Windsor <dwindsor@gmail.com>,
x86@kernel.org, Ingo Molnar <mingo@kernel.org>,
Arnd Bergmann <arnd@arndb.de>,
Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
Jann Horn <jann@thejh.net>,
davem@davemloft.net, linux-arch@vger.kernel.org,
kernel-hardening@lists.openwall.com,
PaX Team <pageexec@freemail.hu>
Subject: Re: [PATCH] x86/refcount: Implement fast refcount_t handling
Date: Mon, 24 Apr 2017 10:32:50 +0200 [thread overview]
Message-ID: <20170424083250.h2wv2exbi4ytigac@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <20170421220939.GA65363@beast>
On Fri, Apr 21, 2017 at 03:09:39PM -0700, Kees Cook wrote:
> This patch ports the x86-specific atomic overflow handling from PaX's
> PAX_REFCOUNT to the upstream refcount_t API. This is an updated version
> from PaX that eliminates the saturation race condition by resetting the
> atomic counter back to the INT_MAX saturation value on both overflow and
> underflow. To win a race, a system would have to have INT_MAX threads
> simultaneously overflow before the saturation handler runs.
And is this impossible? Highly unlikely I'll grant you, but absolutely
impossible?
Also, you forgot nr_cpus in your bound. Afaict the worst case here is
O(nr_tasks + 3*nr_cpus).
Because PaX does it, is not a correctness argument. And this really
wants one.
next prev parent reply other threads:[~2017-04-24 8:33 UTC|newest]
Thread overview: 28+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-04-21 22:09 Kees Cook
2017-04-24 8:32 ` Peter Zijlstra [this message]
2017-04-24 8:53 ` [kernel-hardening] " Jann Horn
2017-04-24 9:20 ` Peter Zijlstra
2017-04-24 11:00 ` PaX Team
2017-04-24 11:15 ` Peter Zijlstra
2017-04-24 13:08 ` PaX Team
2017-04-24 13:33 ` Peter Zijlstra
2017-04-24 15:15 ` PaX Team
2017-04-24 20:40 ` Kees Cook
2017-04-24 22:01 ` Peter Zijlstra
2017-04-24 22:37 ` Kees Cook
2017-04-25 1:11 ` [kernel-hardening] " Rik van Riel
2017-04-25 9:05 ` Peter Zijlstra
2017-04-25 11:26 ` PaX Team
2017-04-25 16:36 ` Kees Cook
2017-04-24 20:33 ` Kees Cook
2017-04-25 11:26 ` PaX Team
2017-04-25 16:39 ` Kees Cook
2017-04-26 2:14 ` PaX Team
2017-04-26 4:42 ` Kees Cook
2017-04-24 20:16 ` Kees Cook
2017-04-24 10:45 ` Peter Zijlstra
2017-04-24 20:19 ` Kees Cook
2017-04-24 10:48 ` Peter Zijlstra
2017-04-24 20:21 ` Kees Cook
2017-04-25 10:23 ` Peter Zijlstra
2017-04-25 11:26 ` PaX Team
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