Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757322AbbKFMMu (ORCPT ); Fri, 6 Nov 2015 07:12:50 -0500 Received: from mx1.redhat.com ([209.132.183.28]:52771 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752346AbbKFMMt (ORCPT ); Fri, 6 Nov 2015 07:12:49 -0500 Date: Fri, 6 Nov 2015 06:12:47 -0600 From: Josh Poimboeuf To: Petr Mladek Cc: Seth Jennings , Jiri Kosina , Vojtech Pavlik , linux-kernel@vger.kernel.org, live-patching@vger.kernel.org, "Cyril B." , Rusty Russell , Miroslav Benes Subject: Re: [PATCH v2 3/3] livepatch: Cleanup module page permission changes Message-ID: <20151106121247.GF28254@treble.redhat.com> References: <20151106104055.GL2599@pathway.suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20151106104055.GL2599@pathway.suse.cz> User-Agent: Mutt/1.5.23.1-rc1 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2277 Lines: 56 On Fri, Nov 06, 2015 at 11:40:55AM +0100, Petr Mladek wrote: > On Thu 2015-11-05 15:18:05, Josh Poimboeuf wrote: > > Calling set_memory_rw() and set_memory_ro() for every iteration of the > > loop in klp_write_object_relocations() is messy, inefficient, and > > error-prone. > > > > Change all the read-only pages to read-write before the loop and convert > > them back to read-only again afterwards. > > > > The {un}set_module_core_ro_nx() functions are used to change the > > page permissions. Toggling NX isn't necessary in this case, but it's > > not highly performance sensitive code so it should be fine. > > Hmm, the name (un)set_module_core_ro_nx() still sounds a bit strange, > especially the "ro_nx" suffix. > Alternative solution would be to create > > set_module_text_rw() > set_module_text_ro() > > There already exists > > set_all_modules_text_rw() > set_all_modules_text_ro() > > They modify only the ro/rw flags. IMHO, the name is more descriptive > They are used by ftrace for very similar purpose. That wouldn't be enough. Relocations can occur not only in text, but also in data. That includes read-only data. The (un)set_module_core_ro_nx() naming was taken from the names of existing module functions (unset_module_{core,init}_ro_nx()). They enable/disable the CONFIG_DEBUG_SET_MODULE_RONX feature on the core part of the module. The name makes sense to me, though I'm certainly open to other ideas. > They modify also the init section. But we might want to touch it > as well. klp_module_notify() is called too late now. But once we > have a more complex consistency model, we will need to reject > the module when the patching fails. We will need to call the > livepatch init earlier, close to ftrace_module_init(mod). > Then the init section might be interesting as well. Init section functions don't have the __fentry() call, so they can't be patched. If that were to change in the future, we could use the (un)set_module_init_ro_nx() functions, which already exist. -- Josh -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/