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

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Date:	Tue, 15 Jul 2014 18:32:23 +0400
From:	Andrey Ryabinin <a.ryabinin@...sung.com>
To:	Christoph Lameter <cl@...two.org>,
	Andrey Ryabinin <ryabinin.a.a@...il.com>
Cc:	"H. Peter Anvin" <hpa@...or.com>, linux-kernel@...r.kernel.org,
	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>,
	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 07/14/14 19:13, Christoph Lameter wrote:
> On Sun, 13 Jul 2014, Andrey Ryabinin wrote:
> 
>>> How does that work when memory is sparsely populated?
>>>
>>
>> Sparsemem configurations currently may not work with kasan.
>> I suppose I will have to move shadow area to vmalloc address space and
>> make it (shadow) sparse too if needed.
> 
> Well it seems to work with sparsemem / vmemmap? So non vmmemmapped configs
> of sparsemem only. vmemmmap can also handle holes in memory.
> 
> 

Not sure. This sparsemem/vmemmap thing is kinda new to me, so I need to dig some more
to understand how it iтteracts with kasan.

As far as I understand the main problem with sparsemem & kasan is shadow allocation:

	unsigned long lowmem_size = (unsigned long)high_memory - PAGE_OFFSET;
	shadow_size = lowmem_size >> KASAN_SHADOW_SCALE_SHIFT;

	shadow_phys_start = memblock_alloc(shadow_size, PAGE_SIZE);

If we don't have one big enough physically contiguous block for shadow it will fail.

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