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

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Date:	Sun, 26 Apr 2015 13:12:26 -0700
From:	Andi Kleen <andi@...stfloor.org>
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>,
	David Rientjes <rientjes@...gle.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

Anisse Astier <anisse@...ier.eu> writes:
> +	  If unsure, say N.
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 05fcec9..c71440a 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -803,6 +803,11 @@ static bool free_pages_prepare(struct page *page, unsigned int order)
>  		debug_check_no_obj_freed(page_address(page),
>  					   PAGE_SIZE << order);
>  	}
> +
> +#ifdef CONFIG_SANITIZE_FREED_PAGES
> +	zero_pages(page, order);
> +#endif

And not removing the clear on __GFP_ZERO by remembering that?

That means all clears would be done twice. 

That patch is far too simple. Clearing is commonly the most
expensive kernel operation.

-Andi

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