linux-kernel - Re: [RFC/PATCH -next 00/21] Address sanitizer for kernel (kasan)

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Message-ID: <53C08876.10209@zytor.com>
Date:	Fri, 11 Jul 2014 17:59:34 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Andrey Ryabinin <a.ryabinin@...sung.com>,
	linux-kernel@...r.kernel.org
CC:	Dmitry Vyukov <dvyukov@...gle.com>,
	Konstantin Serebryany <kcc@...gle.com>,
	Alexey Preobrazhensky <preobr@...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>,
	Russell King <linux@....linux.org.uk>,
	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>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kbuild@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	x86@...nel.org, linux-mm@...ck.org
Subject: Re: [RFC/PATCH -next 00/21] Address sanitizer for kernel (kasan)
 - dynamic memory error detector.

On 07/09/2014 04:00 AM, Andrey Ryabinin wrote:
> 
> Address sanitizer dedicates 1/8 of the low memory to the shadow memory and uses direct
> mapping with a scale and offset to translate a memory address to its corresponding
> shadow address.
> 
> Here is function to translate address to corresponding shadow address:
> 
>      unsigned long kasan_mem_to_shadow(unsigned long addr)
>      {
> 		return ((addr) >> KASAN_SHADOW_SCALE_SHIFT)
>        	             + kasan_shadow_start - (PAGE_OFFSET >> KASAN_SHADOW_SCALE_SHIFT);
>      }
> 
> where KASAN_SHADOW_SCALE_SHIFT = 3.
> 

How does that work when memory is sparsely populated?

	-hpa

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