linux-kernel - Re: [PATCH v3 2/4] PM / Hibernate: prepare for SANITIZE_FREED

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Date:	Wed, 13 May 2015 11:50:20 +0200
From:	"PaX Team" <pageexec@...email.hu>
To:	Pavel Machek <pavel@....cz>, Anisse Astier <anisse@...ier.eu>
CC:	Andrew Morton <akpm@...ux-foundation.org>,
	Mel Gorman <mgorman@...e.de>,
	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
	David Rientjes <rientjes@...gle.com>,
	Alan Cox <gnomes@...rguk.ukuu.org.uk>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Brad Spengler <spender@...ecurity.net>,
	Kees Cook <keescook@...omium.org>,
	Andi Kleen <andi@...stfloor.org>,
	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	Len Brown <len.brown@...el.com>, linux-mm@...ck.org,
	Linux PM list <linux-pm@...r.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Mathias Krause <minipli@...glemail.com>
Subject: Re: [PATCH v3 2/4] PM / Hibernate: prepare for SANITIZE_FREED_PAGES

On 11 May 2015 at 9:59, Anisse Astier wrote:

> > Otherwise it looks good to me... if the sanitization is considered
> > useful. Did it catch some bugs in the past?
> >
> 
> I've read somewhere that users of grsecurity claim that it caught bugs
> in some drivers, but I haven't verified that personally; it's probably
> much less useful than kasan (or even the original grsec feature) as a
> bug-catcher since it doesn't clear freed slab buffers.

the PaX SANITIZE feature wasn't developed for catching use-after-free bugs
but to help reduce data lifetime from the kernel while not killing too much
performance (this is why i was reluctant to add a finer grained version to
do slab object sanitization until Mathias Krause came up with a workable
compromise).

another reason page zeroing isn't good at catching these bugs is that the
0 fill value will produce NULL pointers which are often explicitly handled
already. on the other hand changing the fill value would not allow the
__GFP_ZERO performance optimization (the slab sanitization feature is a
different story however, we have a non-0 fill value and it keeps triggering
use-after-free bugs).

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