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Date: Mon, 11 May 2015 20:55:27 +0800
From: Minfei Huang <minfei.huang@...mail.com>
To: Miroslav Benes <mbenes@...e.cz>
CC: Minfei Huang <mhuang@...hat.com>, jpoimboe@...hat.com,
sjenning@...hat.com, jkosina@...e.cz, vojtech@...e.cz,
live-patching@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] livepatch: Prevent to enable uninitialized patch
On 05/11/15 at 02:02P, Miroslav Benes wrote:
> On Mon, 11 May 2015, Minfei Huang wrote:
>
> > From: Minfei Huang <minfei.huang@...mail.com>
> >
> > 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 <minfei.huang@...mail.com>
>
> 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@...r.kernel.org
> > More majordomo info at http://vger.kernel.org/majordomo-info.html
> >
>
> --
> Miroslav Benes
> SUSE Labs
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