linux-kernel - Re: [PATCH v10 02/17] x86

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Date:	Thu, 29 Jan 2015 15:12:24 -0800
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Andrey Ryabinin <a.ryabinin@...sung.com>
Cc:	linux-kernel@...r.kernel.org, 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>,
	Christoph Lameter <cl@...ux.com>,
	Joonsoo Kim <iamjoonsoo.kim@....com>,
	Dave Hansen <dave.hansen@...el.com>,
	Andi Kleen <andi@...stfloor.org>, x86@...nel.org,
	linux-mm@...ck.org, Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>, Jonathan Corbet <corbet@....net>,
	Andy Lutomirski <luto@...capital.net>,
	linux-doc@...r.kernel.org (open list:DOCUMENTATION)
Subject: Re: [PATCH v10 02/17] x86_64: add KASan support

On Thu, 29 Jan 2015 18:11:46 +0300 Andrey Ryabinin <a.ryabinin@...sung.com> wrote:

> This patch adds arch specific code for kernel address sanitizer.
> 
> 16TB of virtual addressed used for shadow memory.
> It's located in range [ffffec0000000000 - fffffc0000000000]
> between vmemmap and %esp fixup stacks.
> 
> At early stage we map whole shadow region with zero page.
> Latter, after pages mapped to direct mapping address range
> we unmap zero pages from corresponding shadow (see kasan_map_shadow())
> and allocate and map a real shadow memory reusing vmemmap_populate()
> function.
> 
> Also replace __pa with __pa_nodebug before shadow initialized.
> __pa with CONFIG_DEBUG_VIRTUAL=y make external function call (__phys_addr)
> __phys_addr is instrumented, so __asan_load could be called before
> shadow area initialized.
> 
> ...
>
> --- a/lib/Kconfig.kasan
> +++ b/lib/Kconfig.kasan
> @@ -5,6 +5,7 @@ if HAVE_ARCH_KASAN
>  
>  config KASAN
>  	bool "AddressSanitizer: runtime memory debugger"
> +	depends on !MEMORY_HOTPLUG
>  	help
>  	  Enables address sanitizer - runtime memory debugger,
>  	  designed to find out-of-bounds accesses and use-after-free bugs.

That's a significant restriction.  It has obvious runtime implications.
It also means that `make allmodconfig' and `make allyesconfig' don't
enable kasan, so compile coverage will be impacted.

This wasn't changelogged.  What's the reasoning and what has to be done
to fix it?
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