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List:       live-patching
Subject:    Re: [PATCH v2 1/2] module: Add a new helper delete_module()
From:       Yafang Shao <laoar.shao () gmail ! com>
Date:       2024-04-24 12:09:05
Message-ID: CALOAHbDGcY5y6hWZgJp9ELrt_w4pfB-X3EqS3yu8k37pj3ZEcw () mail ! gmail ! com
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On Sun, Apr 7, 2024 at 11:58 AM Yafang Shao <laoar.shao@gmail.com> wrote:
> 
> Introduce a new helper function, delete_module(), designed to delete kernel
> modules from locations outside of the `kernel/module` directory.
> 
> No functional change.
> 
> Signed-off-by: Yafang Shao <laoar.shao@gmail.com>
> ---
> include/linux/module.h |  1 +
> kernel/module/main.c   | 82 ++++++++++++++++++++++++++++++++----------
> 2 files changed, 65 insertions(+), 18 deletions(-)
> 
> diff --git a/include/linux/module.h b/include/linux/module.h
> index 1153b0d99a80..c24557f1b795 100644
> --- a/include/linux/module.h
> +++ b/include/linux/module.h
> @@ -75,6 +75,7 @@ extern struct module_attribute module_uevent;
> /* These are either module local, or the kernel's dummy ones. */
> extern int init_module(void);
> extern void cleanup_module(void);
> +extern int delete_module(struct module *mod);
> 
> #ifndef MODULE
> /**
> diff --git a/kernel/module/main.c b/kernel/module/main.c
> index e1e8a7a9d6c1..3b48ee66db41 100644
> --- a/kernel/module/main.c
> +++ b/kernel/module/main.c
> @@ -695,12 +695,74 @@ EXPORT_SYMBOL(module_refcount);
> /* This exists whether we can unload or not */
> static void free_module(struct module *mod);
> 
> +static void __delete_module(struct module *mod)
> +{
> +       char buf[MODULE_FLAGS_BUF_SIZE];
> +
> +       WARN_ON_ONCE(mod->state != MODULE_STATE_GOING);
> +
> +       /* Final destruction now no one is using it. */
> +       if (mod->exit != NULL)
> +               mod->exit();
> +       blocking_notifier_call_chain(&module_notify_list,
> +                                    MODULE_STATE_GOING, mod);
> +       klp_module_going(mod);
> +       ftrace_release_mod(mod);
> +
> +       async_synchronize_full();
> +
> +       /* Store the name and taints of the last unloaded module for diagnostic \
> purposes */ +       strscpy(last_unloaded_module.name, mod->name, \
> sizeof(last_unloaded_module.name)); +       strscpy(last_unloaded_module.taints, \
> module_flags(mod, buf, false), +               \
> sizeof(last_unloaded_module.taints)); +
> +       free_module(mod);
> +       /* someone could wait for the module in add_unformed_module() */
> +       wake_up_all(&module_wq);
> +}
> +
> +int delete_module(struct module *mod)
> +{
> +       int ret;
> +
> +       mutex_lock(&module_mutex);
> +       if (!list_empty(&mod->source_list)) {
> +               /* Other modules depend on us: get rid of them first. */
> +               ret = -EWOULDBLOCK;
> +               goto out;
> +       }
> +
> +       /* Doing init or already dying? */
> +       if (mod->state != MODULE_STATE_LIVE) {
> +               ret = -EBUSY;
> +               goto out;
> +       }
> +
> +       /* If it has an init func, it must have an exit func to unload */
> +       if (mod->init && !mod->exit) {
> +               ret = -EBUSY;
> +               goto out;
> +       }
> +
> +       if (try_release_module_ref(mod) != 0) {
> +               ret = -EWOULDBLOCK;
> +               goto out;
> +       }
> +       mod->state = MODULE_STATE_GOING;
> +       mutex_unlock(&module_mutex);
> +       __delete_module(mod);
> +       return 0;
> +
> +out:
> +       mutex_unlock(&module_mutex);
> +       return ret;
> +}
> +
> SYSCALL_DEFINE2(delete_module, const char __user *, name_user,
> unsigned int, flags)
> {
> struct module *mod;
> char name[MODULE_NAME_LEN];
> -       char buf[MODULE_FLAGS_BUF_SIZE];
> int ret, forced = 0;
> 
> if (!capable(CAP_SYS_MODULE) || modules_disabled)
> @@ -750,23 +812,7 @@ SYSCALL_DEFINE2(delete_module, const char __user *, name_user,
> goto out;
> 
> mutex_unlock(&module_mutex);
> -       /* Final destruction now no one is using it. */
> -       if (mod->exit != NULL)
> -               mod->exit();
> -       blocking_notifier_call_chain(&module_notify_list,
> -                                    MODULE_STATE_GOING, mod);
> -       klp_module_going(mod);
> -       ftrace_release_mod(mod);
> -
> -       async_synchronize_full();
> -
> -       /* Store the name and taints of the last unloaded module for diagnostic \
>                 purposes */
> -       strscpy(last_unloaded_module.name, mod->name, \
>                 sizeof(last_unloaded_module.name));
> -       strscpy(last_unloaded_module.taints, module_flags(mod, buf, false), \
>                 sizeof(last_unloaded_module.taints));
> -
> -       free_module(mod);
> -       /* someone could wait for the module in add_unformed_module() */
> -       wake_up_all(&module_wq);
> +       __delete_module(mod);
> return 0;
> out:
> mutex_unlock(&module_mutex);
> --
> 2.39.1
> 

Luis, Greg,

Since the last version, there hasn't been any response. Would you mind
taking a moment to review it and provide your feedback on the
kernel/module changes?

-- 
Regards
Yafang


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