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From: "PaX Team" <pageexec@freemail.hu>
Date: Mon, 04 May 2015 23:50:14 +0200
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Subject: Re: [PATCH v2 4/4] mm: Add debug code for SANITIZE_FREED_PAGES
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In-reply-to: <1430774218-5311-5-git-send-email-anisse@astier.eu>
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To: Anisse Astier <anisse@astier.eu>
Cc: Andrew Morton <akpm@linux-foundation.org>, Mel Gorman <mgorman@suse.de>, "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>, David Rientjes <rientjes@google.com>, Alan Cox <gnomes@lxorguk.ukuu.org.uk>, Linus Torvalds <torvalds@linux-foundation.org>, Peter Zijlstra <peterz@infradead.org>, Brad Spengler <spender@grsecurity.net>, Kees Cook <keescook@chromium.org>, Andi Kleen <andi@firstfloor.org>, linux-mm@kvack.org, linux-kernel@vger.kernel.org

On 4 May 2015 at 23:16, Anisse Astier wrote:

> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index c29e3a0..ba8aa25 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -975,6 +975,31 @@ static int prep_new_page(struct page *page, unsigned int order, gfp_t gfp_flags,
>  		for (i = 0; i < (1 << order); i++)
>  			clear_highpage(page + i);
>  #endif
> +#ifdef CONFIG_SANITIZE_FREED_PAGES_DEBUG
> +	for (i = 0; i < (1 << order); i++) {
> +		struct page *p = page + i;
> +		int j;
> +		bool err = false;
> +		void *kaddr = kmap_atomic(p);
> +
> +		for (j = 0; j < PAGE_SIZE; j++) {

did you mean to use memchr_inv(kaddr, 0, PAGE_SIZE) instead? ;)

> +			if (((char *)kaddr)[j] != 0) {
> +				pr_err("page %p is not zero on alloc! %s\n",
> +						page_address(p), (gfp_flags &
> +							__GFP_ZERO) ?
> +						"fixing." : "");
> +				if (gfp_flags & __GFP_ZERO) {
> +					err = true;
> +					kunmap_atomic(kaddr);
> +					clear_highpage(p);
> +				}
> +				break;
> +			}
> +		}
> +		if (!err)
> +			kunmap_atomic(kaddr);
> +	}
> +#endif
>  
>  	if (order && (gfp_flags & __GFP_COMP))
>  		prep_compound_page(page, order);
> -- 
> 1.9.3
> 
> 



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