Re: [RFC][PATCH 3/4] kprobes: Allow kprobes with CONFIG_MODULES=n

[Christophe Leroy <christophe.leroy@csgroup.eu>]

Le 06/03/2024 à 21:05, Calvin Owens a écrit :
> [Vous ne recevez pas souvent de courriers de jcalvinowens@gmail.com. Découvrez pourquoi ceci est important à https://aka.ms/LearnAboutSenderIdentification ]
> 
> If something like this is merged down the road, it can go in at leisure
> once the module_alloc change is in: it's a one-way dependency.

Too many #ifdef, please reorganise stuff to avoid that and avoid 
changing prototypes based of CONFIG_MODULES.

Other few comments below.

> 
> Signed-off-by: Calvin Owens <jcalvinowens@gmail.com>
> ---
>   arch/Kconfig                |  2 +-
>   kernel/kprobes.c            | 22 ++++++++++++++++++++++
>   kernel/trace/trace_kprobe.c | 11 +++++++++++
>   3 files changed, 34 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/Kconfig b/arch/Kconfig
> index cfc24ced16dd..e60ce984d095 100644
> --- a/arch/Kconfig
> +++ b/arch/Kconfig
> @@ -52,8 +52,8 @@ config GENERIC_ENTRY
> 
>   config KPROBES
>          bool "Kprobes"
> -       depends on MODULES
>          depends on HAVE_KPROBES
> +       select MODULE_ALLOC
>          select KALLSYMS
>          select TASKS_RCU if PREEMPTION
>          help
> diff --git a/kernel/kprobes.c b/kernel/kprobes.c
> index 9d9095e81792..194270e17d57 100644
> --- a/kernel/kprobes.c
> +++ b/kernel/kprobes.c
> @@ -1556,8 +1556,12 @@ static bool is_cfi_preamble_symbol(unsigned long addr)
>                  str_has_prefix("__pfx_", symbuf);
>   }
> 
> +#if IS_ENABLED(CONFIG_MODULES)
>   static int check_kprobe_address_safe(struct kprobe *p,
>                                       struct module **probed_mod)
> +#else
> +static int check_kprobe_address_safe(struct kprobe *p)
> +#endif

A bit ugly to have to change the prototype, why not just keep probed_mod 
at all time ?

When CONFIG_MODULES is not selected, __module_text_address() returns 
NULL so it should work without that many #ifdefs.

>   {
>          int ret;
> 
> @@ -1580,6 +1584,7 @@ static int check_kprobe_address_safe(struct kprobe *p,
>                  goto out;
>          }
> 
> +#if IS_ENABLED(CONFIG_MODULES)
>          /* Check if 'p' is probing a module. */
>          *probed_mod = __module_text_address((unsigned long) p->addr);
>          if (*probed_mod) {
> @@ -1603,6 +1608,8 @@ static int check_kprobe_address_safe(struct kprobe *p,
>                          ret = -ENOENT;
>                  }
>          }
> +#endif
> +
>   out:
>          preempt_enable();
>          jump_label_unlock();
> @@ -1614,7 +1621,9 @@ int register_kprobe(struct kprobe *p)
>   {
>          int ret;
>          struct kprobe *old_p;
> +#if IS_ENABLED(CONFIG_MODULES)
>          struct module *probed_mod;
> +#endif
>          kprobe_opcode_t *addr;
>          bool on_func_entry;
> 
> @@ -1633,7 +1642,11 @@ int register_kprobe(struct kprobe *p)
>          p->nmissed = 0;
>          INIT_LIST_HEAD(&p->list);
> 
> +#if IS_ENABLED(CONFIG_MODULES)
>          ret = check_kprobe_address_safe(p, &probed_mod);
> +#else
> +       ret = check_kprobe_address_safe(p);
> +#endif
>          if (ret)
>                  return ret;
> 
> @@ -1676,8 +1689,10 @@ int register_kprobe(struct kprobe *p)
>   out:
>          mutex_unlock(&kprobe_mutex);
> 
> +#if IS_ENABLED(CONFIG_MODULES)
>          if (probed_mod)
>                  module_put(probed_mod);
> +#endif
> 
>          return ret;
>   }
> @@ -2482,6 +2497,7 @@ int kprobe_add_area_blacklist(unsigned long start, unsigned long end)
>          return 0;
>   }
> 
> +#if IS_ENABLED(CONFIG_MODULES)
>   /* Remove all symbols in given area from kprobe blacklist */
>   static void kprobe_remove_area_blacklist(unsigned long start, unsigned long end)
>   {
> @@ -2499,6 +2515,7 @@ static void kprobe_remove_ksym_blacklist(unsigned long entry)
>   {
>          kprobe_remove_area_blacklist(entry, entry + 1);
>   }
> +#endif
> 
>   int __weak arch_kprobe_get_kallsym(unsigned int *symnum, unsigned long *value,
>                                     char *type, char *sym)
> @@ -2564,6 +2581,7 @@ static int __init populate_kprobe_blacklist(unsigned long *start,
>          return ret ? : arch_populate_kprobe_blacklist();
>   }
> 
> +#if IS_ENABLED(CONFIG_MODULES)
>   static void add_module_kprobe_blacklist(struct module *mod)
>   {
>          unsigned long start, end;
> @@ -2665,6 +2683,7 @@ static struct notifier_block kprobe_module_nb = {
>          .notifier_call = kprobes_module_callback,
>          .priority = 0
>   };
> +#endif /* IS_ENABLED(CONFIG_MODULES) */
> 
>   void kprobe_free_init_mem(void)
>   {
> @@ -2724,8 +2743,11 @@ static int __init init_kprobes(void)
>          err = arch_init_kprobes();
>          if (!err)
>                  err = register_die_notifier(&kprobe_exceptions_nb);
> +
> +#if IS_ENABLED(CONFIG_MODULES)
>          if (!err)
>                  err = register_module_notifier(&kprobe_module_nb);
> +#endif
> 
>          kprobes_initialized = (err == 0);
>          kprobe_sysctls_init();
> diff --git a/kernel/trace/trace_kprobe.c b/kernel/trace/trace_kprobe.c
> index c4c6e0e0068b..dd4598f775b9 100644
> --- a/kernel/trace/trace_kprobe.c
> +++ b/kernel/trace/trace_kprobe.c
> @@ -102,6 +102,7 @@ static nokprobe_inline bool trace_kprobe_has_gone(struct trace_kprobe *tk)
>          return kprobe_gone(&tk->rp.kp);
>   }
> 
> +#if IS_ENABLED(CONFIG_MODULES)
>   static nokprobe_inline bool trace_kprobe_within_module(struct trace_kprobe *tk,
>                                                   struct module *mod)
>   {
> @@ -129,6 +130,12 @@ static nokprobe_inline bool trace_kprobe_module_exist(struct trace_kprobe *tk)
> 
>          return ret;
>   }
> +#else
> +static nokprobe_inline bool trace_kprobe_module_exist(struct trace_kprobe *tk)
> +{
> +       return true;
> +}
> +#endif
> 
>   static bool trace_kprobe_is_busy(struct dyn_event *ev)
>   {
> @@ -670,6 +677,7 @@ static int register_trace_kprobe(struct trace_kprobe *tk)
>          return ret;
>   }
> 
> +#if IS_ENABLED(CONFIG_MODULES)
>   /* Module notifier call back, checking event on the module */
>   static int trace_kprobe_module_callback(struct notifier_block *nb,
>                                         unsigned long val, void *data)
> @@ -704,6 +712,7 @@ static struct notifier_block trace_kprobe_module_nb = {
>          .notifier_call = trace_kprobe_module_callback,
>          .priority = 1   /* Invoked after kprobe module callback */
>   };
> +#endif /* IS_ENABLED(CONFIG_MODULES) */
> 
>   static int count_symbols(void *data, unsigned long unused)
>   {
> @@ -1897,8 +1906,10 @@ static __init int init_kprobe_trace_early(void)
>          if (ret)
>                  return ret;
> 
> +#if IS_ENABLED(CONFIG_MODULES)
>          if (register_module_notifier(&trace_kprobe_module_nb))
>                  return -EINVAL;
Why a #if here ?

If CONFIG_MODULES is not selected, register_module_notifier() return 
always 0.

> +#endif
> 
>          return 0;
>   }
> --
> 2.43.0
> 
>