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

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Date:	Sat, 30 May 2009 03:43:39 -0700
From:	"Larry H." <research@...reption.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Arjan van de Ven <arjan@...radead.org>,
	Alan Cox <alan@...rguk.ukuu.org.uk>,
	Ingo Molnar <mingo@...e.hu>, Rik van Riel <riel@...hat.com>,
	linux-kernel@...r.kernel.org, Linus Torvalds <torvalds@...l.org>,
	linux-mm@...ck.org, Ingo Molnar <mingo@...hat.com>,
	pageexec@...email.hu
Subject: Re: [patch 0/5] Support for sanitization flag in low-level page
	allocator

On 12:39 Sat 30 May     , Peter Zijlstra wrote:
> > Because zero on allocate kills the very purpose of this patch and it has
> > obvious security implications. Like races (in information leak
> > scenarios, that is). What happens in-between the release of the page and
> > the new allocation that yields the same page? What happens if no further
> > allocations happen in a while (that can return the old page again)?
> > That's the idea.
> 
> I don't get it, these are in-kernel data leaks, you need to be able to
> run kernel code to exploit these, if someone can run kernel code, you've
> lost anyhow.
> 
> Why waste time on this?

If there were any hesitations about your lack of understanding in
security matters, you just cleared them all with the above statements.

> > > So if you zero on free, the next allocation will reuse the zeroed page.
> > > And due to LIFO that is not too far out "often", which makes it likely
> > > the page is still in L2 cache.
> > 
> > Thanks for pointing this out clearly, Arjan.
> 
> Thing is, the time between allocation and use is typically orders of
> magnitude less than between free and use. 
> 
> 
> Really, get a life, go fix real bugs. Don't make our kernel slower for
> wanking rights.

This is exactly the positive attitude, sound and mature response I was
expecting from you. Thank you.

	Larry
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