On Thu 2014-11-06 08:39:08, Seth Jennings wrote:
> This commit introduces code for the live patching core. It implements
> an ftrace-based mechanism and kernel interface for doing live patching
> of kernel and kernel module functions.
>
> It represents the greatest common functionality set between kpatch and
> kgraft and can accept patches built using either method.
>
> This first version does not implement any consistency mechanism that
> ensures that old and new code do not run together. In practice, ~90% of
> CVEs are safe to apply in this way, since they simply add a conditional
> check. However, any function change that can not execute safely with
> the old version of the function can _not_ be safely applied in this
> version.
[...]
> +/******************************
> + * module notifier
> + *****************************/
> +
> +static int lp_module_notify(struct notifier_block *nb, unsigned long action,
> + void *data)
> +{
> + struct module *mod = data;
> + struct lpc_patch *patch;
> + struct lpc_object *obj;
> + int ret = 0;
> +
> + if (action != MODULE_STATE_COMING)
> + return 0;
IMHO, we should handle also MODULE_STATE_GOING. We should unregister
the ftrace handlers and update the state of the affected objects
(ENABLED -> DISABLED)
> + down(&lpc_mutex);
> +
> + list_for_each_entry(patch, &lpc_patches, list) {
> + if (patch->state == DISABLED)
> + continue;
> + list_for_each_entry(obj, &patch->objs, list) {
> + if (strcmp(obj->name, mod->name))
> + continue;
> + pr_notice("load of module '%s' detected, applying patch '%s'\n",
> + mod->name, patch->mod->name);
> + obj->mod = mod;
> + ret = lpc_enable_object(patch->mod, obj);
> + if (ret)
> + goto out;
> + break;
> + }
> + }
> +
> + up(&lpc_mutex);
> + return 0;
> +out:
I would name this err_our or so to make it clear that it is used when
something fails.
> + up(&lpc_mutex);
> + WARN("failed to apply patch '%s' to module '%s'\n",
> + patch->mod->name, mod->name);
> + return 0;
> +}
> +
> +static struct notifier_block lp_module_nb = {
> + .notifier_call = lp_module_notify,
> + .priority = INT_MIN, /* called last */
The handler for MODULE_STATE_COMMING would need have higger priority,
if we want to cleanly unregister the ftrace handlers.
Best Regards,
Petr
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