From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wg0-f48.google.com (mail-wg0-f48.google.com [74.125.82.48]) by kanga.kvack.org (Postfix) with ESMTP id 106E76B006E for ; Mon, 27 Apr 2015 04:12:15 -0400 (EDT) Received: by wgin8 with SMTP id n8so107095514wgi.0 for ; Mon, 27 Apr 2015 01:12:14 -0700 (PDT) Received: from mail-wi0-f169.google.com (mail-wi0-f169.google.com. [209.85.212.169]) by mx.google.com with ESMTPS id em10si32003820wjd.79.2015.04.27.01.12.13 for (version=TLSv1.2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Mon, 27 Apr 2015 01:12:13 -0700 (PDT) Received: by wiun10 with SMTP id n10so80436748wiu.1 for ; Mon, 27 Apr 2015 01:12:12 -0700 (PDT) MIME-Version: 1.0 In-Reply-To: <87tww2ejit.fsf@tassilo.jf.intel.com> References: <1429909549-11726-1-git-send-email-anisse@astier.eu> <1429909549-11726-3-git-send-email-anisse@astier.eu> <87tww2ejit.fsf@tassilo.jf.intel.com> From: Anisse Astier Date: Mon, 27 Apr 2015 10:11:52 +0200 Message-ID: Subject: Re: [PATCH 2/2] mm/page_alloc.c: add config option to sanitize freed pages Content-Type: text/plain; charset=UTF-8 Sender: owner-linux-mm@kvack.org List-ID: To: Andi Kleen Cc: Andrew Morton , Mel Gorman , "Kirill A. Shutemov" , David Rientjes , Alan Cox , Linus Torvalds , Peter Zijlstra , PaX Team , Brad Spengler , Kees Cook , linux-mm@kvack.org, Linux Kernel Mailing List Hi Andi, Thinks for taking the time to review this. On Sun, Apr 26, 2015 at 10:12 PM, Andi Kleen wrote: > Anisse Astier 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. > I thought about this, but if you unconditionally remove the clear on __GFP_ZERO, you wouldn't be guaranteed to have a zeroed page when memory is first used (you would protect the kernel from its own info leaks though); you'd need to clear memory on boot for example. If you try to remember that a page it's cleared, it means using a page flag, which is was previously deemed too precious for this kind of operation. Regarding the expensive operation, I don't think this is an option you'd enable on your systems if you care about performance. Regards, Anisse -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org