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

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Date:	Sun, 31 May 2009 04:58:28 -0700
From:	"Larry H." <research@...reption.com>
To:	Pekka Enberg <penberg@...helsinki.fi>
Cc:	Rik van Riel <riel@...hat.com>, Ingo Molnar <mingo@...e.hu>,
	Alan Cox <alan@...rguk.ukuu.org.uk>,
	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 10:17 Sun 31 May     , Pekka Enberg wrote:
> On Sun, May 31, 2009 at 12:33 AM, Larry H. <research@...reption.com> wrote:
> > While we are at it, did any of you (Pekka, Ingo, Peter) bother reading
> > the very first paper I referenced in the very first patch?:
> >
> > http://www.stanford.edu/~blp/papers/shredding.html/#kernel-appendix
> >
> > Could you _please_ bother your highness with an earthly five minutes
> > read of that paper? If you don't have other magnificent obligations to
> > attend to. _Please_.
> >
> > PS: I'm still thanking myself for not implementing the kthread /
> > multiple page pool based approach. Lord, what could have happened if I
> > did.
> 
> Something like that might make sense for fast-path code.
> 
> I think we could make GFP_SENSITIVE mean that allocations using it
> force the actual slab pages to be cleaned up before they're returned
> to the page allocator. As far as I can tell, we could then recycle
> those slab pages to GFP_SENSITIVE allocations without any clearing
> whatsoever as long as they're managed by slab. This ensures critical
> data in kmalloc()'d memory is never leaked to userspace.
> 
> This doesn't fix all the cases Alan pointed out (unconditional
> memset() in page free is clearly superior from security pov) but
> should allow us to use GFP_SENSITIVE in fast-path cases where the
> overhead of kzfree() is unacceptable.

Thanks for coming to the conclusion that unconditional memory
sanitization is the correct approach.

I thought this had been stated numerous times before in this thread. Are
you serious about your responses or you are just clowning around? It's
amusing, I give you that much.

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