|
Message-ID: <CAGXu5jLY0DpTWhL-CXOF15BvFvQ_4+_pg+vMbuvKqLu9tU_jQw@mail.gmail.com> Date: Mon, 24 Apr 2017 13:16:24 -0700 From: Kees Cook <keescook@...omium.org> To: Peter Zijlstra <peterz@...radead.org> Cc: LKML <linux-kernel@...r.kernel.org>, Eric Biggers <ebiggers3@...il.com>, Christoph Hellwig <hch@...radead.org>, "axboe@...nel.dk" <axboe@...nel.dk>, James Bottomley <James.Bottomley@...senpartnership.com>, Elena Reshetova <elena.reshetova@...el.com>, Hans Liljestrand <ishkamiel@...il.com>, David Windsor <dwindsor@...il.com>, "x86@...nel.org" <x86@...nel.org>, Ingo Molnar <mingo@...nel.org>, Arnd Bergmann <arnd@...db.de>, Greg Kroah-Hartman <gregkh@...uxfoundation.org>, Jann Horn <jann@...jh.net>, "David S. Miller" <davem@...emloft.net>, linux-arch <linux-arch@...r.kernel.org>, "kernel-hardening@...ts.openwall.com" <kernel-hardening@...ts.openwall.com>, PaX Team <pageexec@...email.hu> Subject: Re: [PATCH] x86/refcount: Implement fast refcount_t handling On Mon, Apr 24, 2017 at 1:32 AM, Peter Zijlstra <peterz@...radead.org> wrote: > 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? I'll adjust the language. "Highly unlikely" is still better than "trivially doable with a single thread". :) > 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. Sure, I didn't mean to imply anything other than a demonstration of what PaX is doing (and that it's better than not having it). If we can improve it, that's great. -Kees -- Kees Cook Pixel Security
Powered by blists - more mailing lists
Confused about mailing lists and their use? Read about mailing lists on Wikipedia and check out these guidelines on proper formatting of your messages.