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Message-ID: <20080214130003.4d40d938@laptopd505.fenrus.org>
Date: Thu, 14 Feb 2008 13:00:03 -0800
From: Arjan van de Ven <arjan@...radead.org>
To: Ingo Molnar <mingo@...e.hu>
Cc: pageexec@...email.hu, Sam Ravnborg <sam@...nborg.org>,
linux-kernel@...r.kernel.org, torvalds@...ux-foundation.org,
Thomas Gleixner <tglx@...utronix.de>,
"H. Peter Anvin" <hpa@...or.com>
Subject: Re: [x86.git#mm] stack protector fixes, vmsplice exploit
On Thu, 14 Feb 2008 21:25:35 +0100
Ingo Molnar <mingo@...e.hu> wrote:
>
> * pageexec@...email.hu <pageexec@...email.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.
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