linux-kernel - Re: [patch 0/5] Support for sanitization flag in low-level page allocator

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Message-ID: <4A20EFB7.5050808@cs.helsinki.fi>
Date:	Sat, 30 May 2009 11:35:03 +0300
From:	Pekka Enberg <penberg@...helsinki.fi>
To:	Alan Cox <alan@...rguk.ukuu.org.uk>
CC:	Ingo Molnar <mingo@...e.hu>, Rik van Riel <riel@...hat.com>,
	"Larry H." <research@...reption.com>, linux-kernel@...r.kernel.org,
	Linus Torvalds <torvalds@...l.org>, linux-mm@...ck.org,
	Ingo Molnar <mingo@...hat.com>, pageexec@...email.hu,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [patch 0/5] Support for sanitization flag in low-level page 
 allocator

Hi Alan,

Alan Cox wrote:
> The problem is that most sensitive data is user space anyway.
> GFP_SENSITIVE or kzfree mean you have to get it right in the kernel and
> you don't fix things like stack copies of sensitive data - its a quick
> hack which doesn't meet goot security programming practice -it defaults
> to insecure which is the wrong way around. Not saying its not a bad idea
> to kzfree a few keys and things *but* it's not real security.
> 
> If you want to do real security you have a sysfs or build flag that turns
> on clearing every page on free. Yes it costs performance (a lot less
> nowdays with cache bypassing stores) but for the category of user who
> wants to be sure nothing escapes it does the job while kzfree would be
> like trying to plug leaks in a sieve.

Yup, your suggestion would make one simple patch, for sure. I wonder if 
anyone is actually prepared to enable the thing at run-time, though, 
which is why I suggested doing the "critical" kzfree() ones unconditionally.

			Pekka
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