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

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Date:	Sun, 31 May 2009 11:24:40 +0100
From:	Alan Cox <alan@...rguk.ukuu.org.uk>
To:	Pekka Enberg <penberg@...helsinki.fi>
Cc:	Rik van Riel <riel@...hat.com>, Ingo Molnar <mingo@...e.hu>,
	"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

> On Sun, May 31, 2009 at 2:10 AM, Alan Cox <alan@...rguk.ukuu.org.uk> wrote:
> > #2 Using kzfree() to clear specific bits of memory (and I question the
> > kzfree implementation as it seems ksize can return numbers much much
> > bigger than the allocated space you need to clear - correct but oversize)
> > or using other flags. I'd favour kzfree personally (and fixing it to work
> > properly)
> 
> Well, yes, that's what kzfree() needs to do given the current API. I
> am not sure why you think it's a problem, though. Adding a size
> argument to the function will make it more error prone.

Definitely - am I right however that 

	x = kzalloc(size, flags)
	blah
	kzfree(x)

can memset a good deal more memory (still safely) than "size" to zero ?
That has performance relevance if so and it ought to at least be
documented.

> On Sun, May 31, 2009 at 2:10 AM, Alan Cox <alan@...rguk.ukuu.org.uk> wrote:
> > #3 People wanting to be able to select for more security *irrespective*
> > of performance cost. Which is no different to SELinux for example.
> 
> Yeah, as I said before, I really don't have any objections to this. I
> just think nobody is going to enable it so memset() or kzfree() in
> relevant places is probably a good idea.

Agreed entirely.
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