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Message-ID: <4F168E93.5010000@parallels.com>
Date: Wed, 18 Jan 2012 13:19:15 +0400
From: Pavel Emelyanov <xemul@parallels.com>
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To: KOSAKI Motohiro <kosaki.motohiro@gmail.com>
CC: Cyrill Gorcunov <gorcunov@gmail.com>,
        "Eric W. Biederman" <ebiederm@xmission.com>,
        "H. Peter Anvin" <hpa@zytor.com>,
        Alexey Dobriyan <adobriyan@gmail.com>,
        LKML <linux-kernel@vger.kernel.org>, Andrey Vagin <avagin@openvz.org>,
        Ingo Molnar <mingo@elte.hu>, Thomas Gleixner <tglx@linutronix.de>,
        Glauber Costa <glommer@parallels.com>,
        Andi Kleen <andi@firstfloor.org>, Tejun Heo <tj@kernel.org>,
        Matt Helsley <matthltc@us.ibm.com>, Pekka Enberg <penberg@kernel.org>,
        Eric Dumazet <eric.dumazet@gmail.com>,
        Vasiliy Kulikov <segoon@openwall.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        "Valdis.Kletnieks@vt.edu" <Valdis.Kletnieks@vt.edu>
Subject: Re: [RFC] syscalls, x86: Add __NR_kcmp syscall
References: <20120117142759.GE16213@moon> <CACVxJT8TJXopJ5-_0j=6CsWXJL8wMOFCerfvmhWa7wcYnejFEg@mail.gmail.com> <20120117144452.GG16213@moon> <4F15C249.3000602@zytor.com> <m1obu29fnf.fsf@fess.ebiederm.org> <20120118080103.GA2889@moon> <4F168CF3.5090400@gmail.com>
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> I think Eric only said gt/lt compare is useful. We don't need to expose bare
> pointer order. example, kcmp(rotate(ptr, per-task-random-value)) is enough
> hide the critical information. I think.

The per-task might break thinks up in case

(tsk1->file != tsk2->file) && (rotate(tsk1->file, tsk1->random) == rotate(tsk2->file, tsk2->rotate))

but I agree, that the overall idea of comparing not bare pointers, but those poisoned with
some global value can address the Peter's concerns about rootkits.

Thanks,
Pavel