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

[Calvin Owens <jcalvinowens@gmail.com>]

On Thursday 03/07 at 22:16 +0000, Christophe Leroy wrote:
> 
> 
> 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.

TBH the ugliness here was just me trying not to trigger -Wunused, but
that was silly: as you point out below, it's unncessary. I'll clean it
up.

> > 
> > 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
> > 
> >