Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1161454AbbKFNmt (ORCPT ); Fri, 6 Nov 2015 08:42:49 -0500 Received: from mx2.suse.de ([195.135.220.15]:58018 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932883AbbKFNms (ORCPT ); Fri, 6 Nov 2015 08:42:48 -0500 Date: Fri, 6 Nov 2015 14:42:46 +0100 From: Petr Mladek To: Josh Poimboeuf 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: <20151106134246.GM2599@pathway.suse.cz> References: <20151106104055.GL2599@pathway.suse.cz> <20151106121247.GF28254@treble.redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20151106121247.GF28254@treble.redhat.com> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2846 Lines: 82 On Fri 2015-11-06 06:12:47, Josh Poimboeuf wrote: > 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. I see. This just shows how this all is confusing. Or maybe I am just dumb :-) > 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. I think that we should not mix set_*_ro() set_*_rw() with set_*_ro*() unset_*_ro*() naming schemes. What about adding into the public API? set_module_ro() set_module_rw() It should modify everything: init, core, text, and data but only the ro/rw flags. Sigh, we went quite far from the few lines patch :-/ > > 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. I see. Best Regards, Petr -- 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/