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From: Arjan van de Ven <arjan@infradead.org>
To: Ingo Molnar <mingo@elte.hu>
Cc: pageexec@freemail.hu, Sam Ravnborg <sam@ravnborg.org>,
	linux-kernel@vger.kernel.org, torvalds@linux-foundation.org,
	Thomas Gleixner <tglx@linutronix.de>,
	"H. Peter Anvin" <hpa@zytor.com>
Subject: Re: [x86.git#mm] stack protector fixes, vmsplice exploit
Date: Thu, 14 Feb 2008 13:00:03 -0800	[thread overview]
Message-ID: <20080214130003.4d40d938@laptopd505.fenrus.org> (raw)
In-Reply-To: <20080214202535.GA25316@elte.hu>

On Thu, 14 Feb 2008 21:25:35 +0100
Ingo Molnar <mingo@elte.hu> wrote:

> 
> * pageexec@freemail.hu <pageexec@freemail.hu> wrote:
> 
> > really, the best defense is to reduce the useful lifetime of any 
> > leaked canary, and you can't get better than syscall granularity 
> > without disproportional effort and impact elsewhere (and i'm sure
> > some would find even this disproportional ;).
> 
> hm, i think per syscall canaries are really expensive.


it's not that bad. Assuming you use a PNR that you re-seed periodically,
it's 
* go to the next random number with PNR
* write to PDA and task struct

give or take 10 cycles total if you squeeze it hard, 20 if you don't.

  reply	other threads:[~2008-02-14 21:02 UTC|newest]

Thread overview: 11+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2008-02-14 17:00 Ingo Molnar
2008-02-14 17:16 ` pageexec
2008-02-14 19:00   ` Ingo Molnar
2008-02-14 18:55     ` pageexec
2008-02-14 20:25       ` Ingo Molnar
2008-02-14 21:00         ` Arjan van de Ven [this message]
2008-02-14 21:12         ` pageexec
2008-02-14 22:35         ` Jakub Jelinek
2008-02-14 21:43           ` pageexec
2008-02-14 23:19             ` Ingo Molnar
2008-02-14 23:16           ` Ingo Molnar

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