Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753508AbbEKMzY (ORCPT ); Mon, 11 May 2015 08:55:24 -0400 Received: from blu004-omc4s12.hotmail.com ([65.55.111.151]:64640 "EHLO BLU004-OMC4S12.hotmail.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751962AbbEKMzW (ORCPT ); Mon, 11 May 2015 08:55:22 -0400 X-TMN: [3ntToxI5MFN2kHIcYoLXk6Fp3dfB8F+M] X-Originating-Email: [minfei.huang@hotmail.com] Message-ID: Date: Mon, 11 May 2015 20:55:27 +0800 From: Minfei Huang To: Miroslav Benes CC: Minfei Huang , jpoimboe@redhat.com, sjenning@redhat.com, jkosina@suse.cz, vojtech@suse.cz, live-patching@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] livepatch: Prevent to enable uninitialized patch References: <1431313066-3102-1-git-send-email-mhuang@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.23 (2014-03-12) X-OriginalArrivalTime: 11 May 2015 12:55:20.0093 (UTC) FILETIME=[BC8FDCD0:01D08BE9] Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 5602 Lines: 159 On 05/11/15 at 02:02P, Miroslav Benes wrote: > On Mon, 11 May 2015, Minfei Huang wrote: > > > From: Minfei Huang > > > > The previous patches can be applied, while the corresponding module is > > loaded. Now the code cannot handle correct behavior to deal with the > > case that the patch fail to be initialized when the module is being > > loaded. > > > > In general, the patch will do relocation (if necessary) and > > obtain/verify function address before we start to enable patch. But we > > can still trigger to enable the patch (disable the patch firstly, then > > enable it), although the patch fail to be initialized in the function > > klp_module_notify_coming. > > > > To fix it, we can make obj->mod to NULL, if the object fails to be > > initialized. > > Hi, Miroslav. This patch is used to prevent the patch to be enabled. I will use the code to explain what I want to show you. 1) Patched a patch to fix the issue for module A. 2) livepatch will try to enable the patch, while the corresponding module is loaded ( call klp_module_notify_coming ) 3) Firstly, livepatch will do the instruction "obj->mod = mod", whatever the result of klp_module_notify_coming is. 4) livepatch may fail to call the klp_init_object_loaded or klp_enable_object 5) klp_module_notify_coming returns 6) For the userspace, we can enable the patch again ( disable the patch firstly, then enable the patch from the sysfs ) 7) In order to enable the patch, livepatch will call __klp_enable_patch 8) we can pass the limitation (klp_is_object_loaded), because the value of obj->mod is not NULL ( the obj->mod obtains the value from the step 3 ) 9) the patch may be applied, although the patch is not initialized, if the value of func->old_addr is not NULL >From the above description, we can see the uninitialized patch ( the patch should be initialized by the klp_init_object_loaded in general ) can be applied to the kernel. Thanks Minfei > > Signed-off-by: Minfei Huang > > Hi, > > just to be sure, is the following what makes you worried? > > The module comes and our notifier is called. We verify that it needs to be > patched and we call klp_module_notify_coming where the object (for this > module) is enabled. But that could fail somewhere and we print warning to > the log (pr_warn). Now, you can disable and enable patch, during which the > object for this very module is enabled again. And it could fail again. > > Is this correct? Do you want to prevent printing of the warning again and > again to the log? > > It could happen that the first enablement could fail because of something > which would not be true for the second try. In such case the module would > not be patched with your fix (it would be skipped in __klp_enable_patch > loop). > > It is possible that I do not understand the changelog and the patch > correctly, so please shed some light on this if necessary... > > Thanks, > Miroslav > > > --- > > kernel/livepatch/core.c | 23 +++++++++++++---------- > > 1 file changed, 13 insertions(+), 10 deletions(-) > > > > diff --git a/kernel/livepatch/core.c b/kernel/livepatch/core.c > > index 284e269..4bbcdda 100644 > > --- a/kernel/livepatch/core.c > > +++ b/kernel/livepatch/core.c > > @@ -883,30 +883,30 @@ int klp_register_patch(struct klp_patch *patch) > > } > > EXPORT_SYMBOL_GPL(klp_register_patch); > > > > -static void klp_module_notify_coming(struct klp_patch *patch, > > +static int klp_module_notify_coming(struct klp_patch *patch, > > struct klp_object *obj) > > { > > struct module *pmod = patch->mod; > > struct module *mod = obj->mod; > > - int ret; > > + int ret = 0; > > > > ret = klp_init_object_loaded(patch, obj); > > if (ret) > > - goto err; > > + goto out; > > > > if (patch->state == KLP_DISABLED) > > - return; > > + goto out; > > > > pr_notice("applying patch '%s' to loading module '%s'\n", > > pmod->name, mod->name); > > > > ret = klp_enable_object(obj); > > - if (!ret) > > - return; > > > > -err: > > - pr_warn("failed to apply patch '%s' to module '%s' (%d)\n", > > - pmod->name, mod->name, ret); > > +out: > > + if (ret) > > + pr_warn("failed to apply patch '%s' to module '%s' (%d)\n", > > + pmod->name, mod->name, ret); > > + return ret; > > } > > > > static void klp_module_notify_going(struct klp_patch *patch, > > @@ -930,6 +930,7 @@ disabled: > > static int klp_module_notify(struct notifier_block *nb, unsigned long action, > > void *data) > > { > > + int ret = 0; > > struct module *mod = data; > > struct klp_patch *patch; > > struct klp_object *obj; > > @@ -955,7 +956,9 @@ static int klp_module_notify(struct notifier_block *nb, unsigned long action, > > > > if (action == MODULE_STATE_COMING) { > > obj->mod = mod; > > - klp_module_notify_coming(patch, obj); > > + ret = klp_module_notify_coming(patch, obj); > > + if (ret) > > + obj->mod = NULL; > > } else /* MODULE_STATE_GOING */ > > klp_module_notify_going(patch, obj); > > > > -- > > 2.2.2 > > > > -- > > To unsubscribe from this list: send the line "unsubscribe live-patching" in > > the body of a message to majordomo@vger.kernel.org > > More majordomo info at http://vger.kernel.org/majordomo-info.html > > > > -- > Miroslav Benes > SUSE Labs -- 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/