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

[Calvin Owens <jcalvinowens@gmail.com>]

On Friday 03/08 at 11:46 +0900, Masami Hiramatsu wrote:
> On Wed,  6 Mar 2024 12:05:10 -0800
> Calvin Owens <jcalvinowens@gmail.com> wrote:
> 
> > 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.
> > 
> > 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
> 
> OK, if we use EXEC_ALLOC,
> 
> config EXEC_ALLOC
> 	depends on HAVE_EXEC_ALLOC
> 
> And 
> 
>   config KPROBES
>   	bool "Kprobes"
> 	depends on MODULES || EXEC_ALLOC
> 	select EXEC_ALLOC if HAVE_EXEC_ALLOC
> 
> then kprobes can be enabled either modules supported or exec_alloc is supported.
> (new arch does not need to implement exec_alloc)
> 
> Maybe we also need something like
> 
> #ifdef CONFIG_EXEC_ALLOC
> #define module_alloc(size) exec_alloc(size)
> #endif
> 
> in kprobes.h, or just add `replacing module_alloc with exec_alloc` patch.
> 
> Thank you,

The example was helpful, thanks. I see what you mean with
HAVE_EXEC_ALLOC, I'll implement it like that in the next verison.

> >  	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
> >  {
> >  	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;
> > +#endif
> >  
> >  	return 0;
> >  }
> > -- 
> > 2.43.0
> > 
> 
> 
> -- 
> Masami Hiramatsu (Google) <mhiramat@kernel.org>