From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-oi0-f71.google.com (mail-oi0-f71.google.com [209.85.218.71]) by kanga.kvack.org (Postfix) with ESMTP id AFA5B6B0003 for ; Wed, 21 Feb 2018 16:36:42 -0500 (EST) Received: by mail-oi0-f71.google.com with SMTP id 20so1405583oii.1 for ; Wed, 21 Feb 2018 13:36:42 -0800 (PST) Received: from mx1.redhat.com (mx1.redhat.com. [209.132.183.28]) by mx.google.com with ESMTPS id j6si3386851oth.32.2018.02.21.13.36.41 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Wed, 21 Feb 2018 13:36:41 -0800 (PST) Date: Thu, 22 Feb 2018 08:36:29 +1100 From: Dave Chinner Subject: Re: [RFC PATCH v16 0/6] mm: security: ro protection for dynamic data Message-ID: <20180221213629.GF3728@rh> References: <20180212165301.17933-1-igor.stoppa@huawei.com> <20180220012111.GC3728@rh> <24e65dec-f452-a444-4382-d1f88fbb334c@huawei.com> <20180220213604.GD3728@rh> <20180220235600.GA3706@bombadil.infradead.org> <20180221013636.GE3728@rh> <46a9610a-182b-4765-9d83-cab6297377f3@huawei.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <46a9610a-182b-4765-9d83-cab6297377f3@huawei.com> Sender: owner-linux-mm@kvack.org List-ID: To: Igor Stoppa Cc: Matthew Wilcox , Kees Cook , Randy Dunlap , Jonathan Corbet , Michal Hocko , Laura Abbott , Jerome Glisse , Christoph Hellwig , Christoph Lameter , linux-security-module , Linux-MM , LKML , Kernel Hardening On Wed, Feb 21, 2018 at 11:56:22AM +0200, Igor Stoppa wrote: > On 21/02/18 03:36, Dave Chinner wrote: > > On Tue, Feb 20, 2018 at 03:56:00PM -0800, Matthew Wilcox wrote: > >> On Wed, Feb 21, 2018 at 08:36:04AM +1100, Dave Chinner wrote: > >>> FWIW, I'm not wanting to use it to replace static variables. All the > >>> structures are dynamically allocated right now, and get assigned to > >>> other dynamically allocated pointers. I'd likely split the current > >>> structures into a "ro after init" > > I would prefer to use a different terminology, because, if I have > understood the use case, this is not exactly the same as __ro_after_init I want a dynamically allocated "write once" structure. A "write once" structure is, conceptually, is exactly the same as "ro after init". Implementation wise, it may be different to "__ro_after_init", especially when compared to static/global variables. It seems lots of people get confused when discussing concepts vs implementation... :) > >>> ...... > >> > >> No, you'd do: > >> > >> struct xfs_mount_ro { > >> [...] > >> }; > > is this something that is readonly from the beginning and then shared > among mount points or is it specific to each mount point? It's dynamically allocated for each mount point, made read-only before the mount completes and lives for the length of the mount point. > >> struct xfs_mount { > >> const struct xfs_mount_ro *ro; > >> [...] > >> }; > > > > .... so that's pretty much the same thing :P > > The "const" modifier is a nice way to catch errors through the compiler, > iff the ro data will not be initialized through this handle, when it's > still writable. That's kinda implied by the const, isn't it? If we don't do it that way, then the compiler will throw errors.... Cheers, Dave. -- Dave Chinner dchinner@redhat.com -- 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