From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1760078AbdADNln (ORCPT ); Wed, 4 Jan 2017 08:41:43 -0500 Received: from mail3-relais-sop.national.inria.fr ([192.134.164.104]:5921 "EHLO mail3-relais-sop.national.inria.fr" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755329AbdADNlk (ORCPT ); Wed, 4 Jan 2017 08:41:40 -0500 X-IronPort-AV: E=Sophos;i="5.33,459,1477954800"; d="scan'208";a="206933691" Date: Wed, 4 Jan 2017 14:41:16 +0100 (CET) From: Julia Lawall X-X-Sender: jll@hadrien To: Russell King - ARM Linux cc: Alexandre Belloni , Kees Cook , andrew@lunn.ch, Jason Cooper , rtc-linux@googlegroups.com, a.zummo@towertech.it, LKML , "linux-arm-kernel@lists.infradead.org" , gregory.clement@free-electrons.com, Bhumika Goyal , sebastian.hesselbarth@gmail.com Subject: Re: [PATCH] rtc: armada38x: add __ro_after_init to armada38x_rtc_ops In-Reply-To: <20170104130628.GQ14217@n2100.armlinux.org.uk> Message-ID: References: <1482751862-18699-1-git-send-email-bhumirks@gmail.com> <20170102140654.GF14217@n2100.armlinux.org.uk> <20170103213118.GM14217@n2100.armlinux.org.uk> <20170103215421.GN14217@n2100.armlinux.org.uk> <20170104110750.dtu54t74qkuuvkvq@piout.net> <20170104121425.GP14217@n2100.armlinux.org.uk> <20170104130628.GQ14217@n2100.armlinux.org.uk> User-Agent: Alpine 2.20 (DEB 67 2015-01-07) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, 4 Jan 2017, Russell King - ARM Linux wrote: > On Wed, Jan 04, 2017 at 01:23:41PM +0100, Julia Lawall wrote: > > Basically, the strategy of the patch is that one may consider it > > preferable to duplicate the structure for the different alternatives, > > rather than use __ro_after_init. Perhaps if the structure were larger, > > then __ro_after_init would be a better choice? > > It depends on not just the size, but how many members need to be > modified, and obviously whether there are likely to be more than one > user of the structure as well. > > So I'd say __ro_after_init rarely makes sense for an operations > structure - the only case I can see is: > > - a large structure > - only a small number of elements need to be modified > - it is only single-use > > which is probably quite rare - this one falls into two out of those > three. > > There's another consideration (imho) too - we may wish, at a later > date, to make .text and .rodata both read-only from the start of the > kernel to harden the kernel against possibly init-time exploitation. > (Think about a buggy built-in driver with emulated hardware - much the > same problem that Kees is trying to address in one of his recent patch > sets but with hotplugged hardware while a screen-saver is active.) > Having function pointers in .rodata rather than the ro-after-init > section would provide better protection. OK, thanks for the explanations. julia