linux-kernel - Re: [PATCH 2/2] mm/page_alloc.c: add config option to sanitize freed pages

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Message-ID: <alpine.DEB.2.10.1504241437070.2456@chino.kir.corp.google.com>
Date:	Fri, 24 Apr 2015 14:38:44 -0700 (PDT)
From:	David Rientjes <rientjes@...gle.com>
To:	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>,
	Alan Cox <gnomes@...rguk.ukuu.org.uk>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Peter Zijlstra <peterz@...radead.org>,
	PaX Team <pageexec@...email.hu>,
	Brad Spengler <spender@...ecurity.net>,
	Kees Cook <keescook@...omium.org>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] mm/page_alloc.c: add config option to sanitize freed
 pages

On Fri, 24 Apr 2015, Anisse Astier wrote:

> diff --git a/mm/Kconfig b/mm/Kconfig
> index 390214d..cb2df5f 100644
> --- a/mm/Kconfig
> +++ b/mm/Kconfig
> @@ -635,3 +635,15 @@ config MAX_STACK_SIZE_MB
>  	  changed to a smaller value in which case that is used.
>  
>  	  A sane initial value is 80 MB.
> +
> +config SANITIZE_FREED_PAGES
> +	bool "Sanitize memory pages after free"
> +	default n
> +	help
> +	  This option is used to make sure all pages freed are zeroed. This is
> +	  quite low-level and doesn't handle your slab buffers.
> +	  It has various applications, from preventing some info leaks to
> +	  helping kernel same-page merging in virtualised environments.
> +	  Depending on your workload, it will reduce performance of about 3%.
> +
> +	  If unsure, say N.

Objection to allowing this without first enabling some other DEBUG config 
option, it should never be a standalone option, but also to pretending to 
have any insight into what the performance degredation of it will be.  On 
my systems, this would be _massive_.
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