linux-kernel - Re: [PATCH v6 00/11] Kernel address sanitizer

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Date:	Tue, 18 Nov 2014 22:15:31 +0100
From:	Andi Kleen <andi@...stfloor.org>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Andrey Ryabinin <a.ryabinin@...sung.com>,
	Dmitry Vyukov <dvyukov@...gle.com>,
	Konstantin Serebryany <kcc@...gle.com>,
	Dmitry Chernenkov <dmitryc@...gle.com>,
	Andrey Konovalov <adech.fo@...il.com>,
	Yuri Gribov <tetra2005@...il.com>,
	Konstantin Khlebnikov <koct9i@...il.com>,
	Sasha Levin <sasha.levin@...cle.com>,
	Michal Marek <mmarek@...e.cz>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	Christoph Lameter <cl@...ux.com>,
	Pekka Enberg <penberg@...nel.org>,
	David Rientjes <rientjes@...gle.com>,
	Joonsoo Kim <iamjoonsoo.kim@....com>,
	Dave Hansen <dave.hansen@...el.com>,
	Andi Kleen <andi@...stfloor.org>,
	Vegard Nossum <vegard.nossum@...il.com>,
	"H. Peter Anvin" <hpa@...or.com>, x86@...nel.org,
	linux-mm@...ck.org, Randy Dunlap <rdunlap@...radead.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Alexander Viro <viro@...iv.linux.org.uk>,
	Dave Jones <davej@...hat.com>,
	Jonathan Corbet <corbet@....net>,
	Joe Perches <joe@...ches.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v6 00/11] Kernel address sanitizer - runtime memory
 debugger.

> It's a huge pile of tricky code we'll need to maintain.  To justify its
> inclusion I think we need to be confident that kasan will find a
> significant number of significant bugs that
> kmemcheck/debug_pagealloc/slub_debug failed to detect.

I would put it differently. kmemcheck is effectively too slow to run
regularly. kasan is much faster and covers most of kmemcheck.

So I would rather see it as a more practical replacement to
kmemcheck, not an addition.

> How do we get that confidence?  I've seen a small number of
> minorish-looking kasan-detected bug reports go past, maybe six or so. 
> That's in a 20-year-old code base, so one new minor bug discovered per
> three years?  Not worth it!
> 
> Presumably more bugs will be exposed as more people use kasan on
> different kernel configs, but will their number and seriousness justify
> the maintenance effort?

I would expect so. It's also about saving developer time.

IMHO getting better tools like this is the only way to keep
up with growing complexity.

> If kasan will permit us to remove kmemcheck/debug_pagealloc/slub_debug
> then that tips the balance a little.  What's the feasibility of that?

Maybe removing kmemcheck. slub_debug/debug_pagealloc are simple, and are in
different niches (lower overhead debugging)

-Andi

-- 
ak@...ux.intel.com -- Speaking for myself only.
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