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

[Masami Hiramatsu (Google) <mhiramat@kernel.org>]

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,

>  	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>