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    SubjectRe: [PATCH] livepatch: Prevent to enable uninitialized patch
    On Mon, 11 May 2015, Minfei Huang wrote:

    > On 05/11/15 at 02:02P, Miroslav Benes wrote:
    > > On Mon, 11 May 2015, Minfei Huang wrote:
    > >
    > > > From: Minfei Huang <minfei.huang@hotmail.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.

    Hi,

    thanks for an explanation. This is really valid.

    Concerning 9), func->old_addr should not be used for the modules (I know
    we had some discussion about that). So it could happen that func->old_addr
    is not initialized as you describe and the user gets warning from
    klp_enable_func. This should be fixed as you proposed.

    Please resend as Jiri requested

    Thanks
    Miroslav

    >
    > Thanks
    > Minfei
    >
    > > > Signed-off-by: Minfei Huang <minfei.huang@hotmail.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@vger.kernel.org
    > > > More majordomo info at http://vger.kernel.org/majordomo-info.html
    > > >
    > >
    > > --
    > > Miroslav Benes
    > > SUSE Labs
    >


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