From mboxrd@z Thu Jan 1 00:00:00 1970 Reply-To: kernel-hardening@lists.openwall.com Date: Fri, 29 Jan 2016 11:45:43 +0100 From: Pavel Machek Message-ID: <20160129104543.GA21224@amd> References: <1454035099-31583-1-git-send-email-labbott@fedoraproject.org> <1454035099-31583-3-git-send-email-labbott@fedoraproject.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1454035099-31583-3-git-send-email-labbott@fedoraproject.org> Subject: [kernel-hardening] Re: [PATCHv2 2/2] mm/page_poisoning.c: Allow for zero poisoning To: Laura Abbott Cc: Andrew Morton , "Kirill A. Shutemov" , Vlastimil Babka , Michal Hocko , "Rafael J. Wysocki" , Len Brown , linux-mm@kvack.org, linux-kernel@vger.kernel.org, kernel-hardening@lists.openwall.com, Kees Cook , linux-pm@vger.kernel.org List-ID: Hi! > By default, page poisoning uses a poison value (0xaa) on free. If this > is changed to 0, the page is not only sanitized but zeroing on alloc > with __GFP_ZERO can be skipped as well. The tradeoff is that detecting > corruption from the poisoning is harder to detect. This feature also > cannot be used with hibernation since pages are not guaranteed to be > zeroed after hibernation. So... this makes kernel harder to debug for performance advantage...? If so.. how big is the performance advantage? Pavel -- (english) http://www.livejournal.com/~pavelmachek (cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html From mboxrd@z Thu Jan 1 00:00:00 1970 From: Pavel Machek Subject: Re: [PATCHv2 2/2] mm/page_poisoning.c: Allow for zero poisoning Date: Fri, 29 Jan 2016 11:45:43 +0100 Message-ID: <20160129104543.GA21224@amd> References: <1454035099-31583-1-git-send-email-labbott@fedoraproject.org> <1454035099-31583-3-git-send-email-labbott@fedoraproject.org> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Received: from atrey.karlin.mff.cuni.cz ([195.113.26.193]:57165 "EHLO atrey.karlin.mff.cuni.cz" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750914AbcA2Kpz (ORCPT ); Fri, 29 Jan 2016 05:45:55 -0500 Content-Disposition: inline In-Reply-To: <1454035099-31583-3-git-send-email-labbott@fedoraproject.org> Sender: linux-pm-owner@vger.kernel.org List-Id: linux-pm@vger.kernel.org To: Laura Abbott Cc: Andrew Morton , "Kirill A. Shutemov" , Vlastimil Babka , Michal Hocko , "Rafael J. Wysocki" , Len Brown , linux-mm@kvack.org, linux-kernel@vger.kernel.org, kernel-hardening@lists.openwall.com, Kees Cook , linux-pm@vger.kernel.org Hi! > By default, page poisoning uses a poison value (0xaa) on free. If this > is changed to 0, the page is not only sanitized but zeroing on alloc > with __GFP_ZERO can be skipped as well. The tradeoff is that detecting > corruption from the poisoning is harder to detect. This feature also > cannot be used with hibernation since pages are not guaranteed to be > zeroed after hibernation. So... this makes kernel harder to debug for performance advantage...? If so.. how big is the performance advantage? Pavel -- (english) http://www.livejournal.com/~pavelmachek (cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wm0-f46.google.com (mail-wm0-f46.google.com [74.125.82.46]) by kanga.kvack.org (Postfix) with ESMTP id 4593A6B0009 for ; Fri, 29 Jan 2016 05:45:54 -0500 (EST) Received: by mail-wm0-f46.google.com with SMTP id 128so47266037wmz.1 for ; Fri, 29 Jan 2016 02:45:54 -0800 (PST) Received: from atrey.karlin.mff.cuni.cz (atrey.karlin.mff.cuni.cz. [195.113.26.193]) by mx.google.com with ESMTP id 190si10157574wmh.45.2016.01.29.02.45.53 for ; Fri, 29 Jan 2016 02:45:53 -0800 (PST) Date: Fri, 29 Jan 2016 11:45:43 +0100 From: Pavel Machek Subject: Re: [PATCHv2 2/2] mm/page_poisoning.c: Allow for zero poisoning Message-ID: <20160129104543.GA21224@amd> References: <1454035099-31583-1-git-send-email-labbott@fedoraproject.org> <1454035099-31583-3-git-send-email-labbott@fedoraproject.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1454035099-31583-3-git-send-email-labbott@fedoraproject.org> Sender: owner-linux-mm@kvack.org List-ID: To: Laura Abbott Cc: Andrew Morton , "Kirill A. Shutemov" , Vlastimil Babka , Michal Hocko , "Rafael J. Wysocki" , Len Brown , linux-mm@kvack.org, linux-kernel@vger.kernel.org, kernel-hardening@lists.openwall.com, Kees Cook , linux-pm@vger.kernel.org Hi! > By default, page poisoning uses a poison value (0xaa) on free. If this > is changed to 0, the page is not only sanitized but zeroing on alloc > with __GFP_ZERO can be skipped as well. The tradeoff is that detecting > corruption from the poisoning is harder to detect. This feature also > cannot be used with hibernation since pages are not guaranteed to be > zeroed after hibernation. So... this makes kernel harder to debug for performance advantage...? If so.. how big is the performance advantage? Pavel -- (english) http://www.livejournal.com/~pavelmachek (cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html -- 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