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

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Date:	Sat, 30 May 2009 10:35:53 +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,

On Thu, May 28, 2009 at 2:50 PM, Alan Cox <alan@...rguk.ukuu.org.uk> wrote:
> The performance cost of such a security action are NIL when the feature
> is disabled. So the performance cost in the general case is irrelevant.
>
> If you need this kind of data wiping then the performance hit
> is basically irrelevant, the security comes first. You can NAK it all you
> like but it simply means that such users either have to apply patches or
> run something else.
>
> If it harmed general user performance you'd have a point - but its like
> SELinux you don't have to use it if you don't need the feature. Which it
> must be said is a lot better than much of the scheduler crud that has
> appeared over time which you can't make go away.

The GFP_SENSITIVE flag looks like a big hammer that we don't really
need IMHO. It seems to me that most of the actual call-sites (crypto
code, wireless keys, etc.) should probably just use kzfree()
unconditionally to make sure we don't leak sensitive data. I did not
look too closely but I don't think any of the sensitive kfree() calls
are in fastpaths so the performance impact is negligible.

                                Pekka
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