Re: [PATCH tip/master 1/3] kprobes: Support blacklist functions in module

[Rusty Russell <rusty@rustcorp.com.au>]

Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com> writes:
> To blacklist the functions in a module (e.g. user-defined
> kprobe handler and the functions invoked from it), expand
> blacklist support for modules.
> With this change, users can use NOKPROBE_SYMBOL() macro in
> their own modules.

Looks great, thanks!

Acked-by: Rusty Russell <rusty@rustcorp.com.au>

> Signed-off-by: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
> Cc: Ananth N Mavinakayanahalli <ananth@in.ibm.com>
> Cc: "David S. Miller" <davem@davemloft.net>
> Cc: Rob Landley <rob@landley.net>
> Cc: Rusty Russell <rusty@rustcorp.com.au>
> ---
>  Documentation/kprobes.txt |    8 ++++++
>  include/linux/module.h    |    4 +++
>  kernel/kprobes.c          |   64 ++++++++++++++++++++++++++++++++++++++-------
>  kernel/module.c           |    6 ++++
>  4 files changed, 72 insertions(+), 10 deletions(-)
>
> diff --git a/Documentation/kprobes.txt b/Documentation/kprobes.txt
> index 1f9b3e2..b5a698f 100644
> --- a/Documentation/kprobes.txt
> +++ b/Documentation/kprobes.txt
> @@ -513,6 +513,14 @@ int enable_jprobe(struct jprobe *jp);
>  Enables *probe which has been disabled by disable_*probe(). You must specify
>  the probe which has been registered.
>  
> +4.9 NOKPROBE_SYMBOL()
> +
> +#include <linux/kprobes.h>
> +NOKPROBE_SYMBOL(FUNCTION);
> +
> +Protects given FUNCTION from other kprobes. This is useful for handler
> +functions and functions called from the handlers.
> +
>  5. Kprobes Features and Limitations
>  
>  Kprobes allows multiple probes at the same address.  Currently,
> diff --git a/include/linux/module.h b/include/linux/module.h
> index d67b193..0827e34 100644
> --- a/include/linux/module.h
> +++ b/include/linux/module.h
> @@ -352,6 +352,10 @@ struct module {
>  	void __percpu *percpu;
>  	unsigned int percpu_size;
>  #endif
> +#ifdef CONFIG_KPROBES
> +	unsigned int num_kprobe_blacklist;
> +	unsigned long  *kprobe_blacklist;
> +#endif
>  
>  #ifdef CONFIG_TRACEPOINTS
>  	unsigned int num_tracepoints;
> diff --git a/kernel/kprobes.c b/kernel/kprobes.c
> index c90e417..53951c3 100644
> --- a/kernel/kprobes.c
> +++ b/kernel/kprobes.c
> @@ -88,6 +88,7 @@ static raw_spinlock_t *kretprobe_table_lock_ptr(unsigned long hash)
>  
>  /* Blacklist -- list of struct kprobe_blacklist_entry */
>  static LIST_HEAD(kprobe_blacklist);
> +static DEFINE_MUTEX(kprobe_blacklist_mutex);
>  
>  #ifdef __ARCH_WANT_KPROBES_INSN_SLOT
>  /*
> @@ -1332,22 +1333,27 @@ bool __weak arch_within_kprobe_blacklist(unsigned long addr)
>  	       addr < (unsigned long)__kprobes_text_end;
>  }
>  
> -static bool within_kprobe_blacklist(unsigned long addr)
> +static struct kprobe_blacklist_entry *find_blacklist_entry(unsigned long addr)
>  {
>  	struct kprobe_blacklist_entry *ent;
>  
> +	list_for_each_entry(ent, &kprobe_blacklist, list) {
> +		if (addr >= ent->start_addr && addr < ent->end_addr)
> +			return ent;
> +	}
> +
> +	return NULL;
> +}
> +
> +static bool within_kprobe_blacklist(unsigned long addr)
> +{
>  	if (arch_within_kprobe_blacklist(addr))
>  		return true;
>  	/*
>  	 * If there exists a kprobe_blacklist, verify and
>  	 * fail any probe registration in the prohibited area
>  	 */
> -	list_for_each_entry(ent, &kprobe_blacklist, list) {
> -		if (addr >= ent->start_addr && addr < ent->end_addr)
> -			return true;
> -	}
> -
> -	return false;
> +	return !!find_blacklist_entry(addr);
>  }
>  
>  /*
> @@ -1437,6 +1443,8 @@ static int check_kprobe_address_safe(struct kprobe *p,
>  	ret = arch_check_ftrace_location(p);
>  	if (ret)
>  		return ret;
> +
> +	mutex_lock(&kprobe_blacklist_mutex);
>  	jump_label_lock();
>  	preempt_disable();
>  
> @@ -1474,6 +1482,7 @@ static int check_kprobe_address_safe(struct kprobe *p,
>  out:
>  	preempt_enable();
>  	jump_label_unlock();
> +	mutex_unlock(&kprobe_blacklist_mutex);
>  
>  	return ret;
>  }
> @@ -2054,13 +2063,13 @@ NOKPROBE_SYMBOL(dump_kprobe);
>   * since a kprobe need not necessarily be at the beginning
>   * of a function.
>   */
> -static int __init populate_kprobe_blacklist(unsigned long *start,
> -					     unsigned long *end)
> +static int populate_kprobe_blacklist(unsigned long *start, unsigned long *end)
>  {
>  	unsigned long *iter;
>  	struct kprobe_blacklist_entry *ent;
>  	unsigned long entry, offset = 0, size = 0;
>  
> +	mutex_lock(&kprobe_blacklist_mutex);
>  	for (iter = start; iter < end; iter++) {
>  		entry = arch_deref_entry_point((void *)*iter);
>  
> @@ -2079,9 +2088,28 @@ static int __init populate_kprobe_blacklist(unsigned long *start,
>  		INIT_LIST_HEAD(&ent->list);
>  		list_add_tail(&ent->list, &kprobe_blacklist);
>  	}
> +	mutex_unlock(&kprobe_blacklist_mutex);
> +
>  	return 0;
>  }
>  
> +/* Shrink the blacklist */
> +static void shrink_kprobe_blacklist(unsigned long *start, unsigned long *end)
> +{
> +	struct kprobe_blacklist_entry *ent;
> +	unsigned long *iter;
> +
> +	mutex_lock(&kprobe_blacklist_mutex);
> +	for (iter = start; iter < end; iter++) {
> +		ent = find_blacklist_entry(*iter);
> +		if (!ent)
> +			continue;
> +		list_del(&ent->list);
> +		kfree(ent);
> +	}
> +	mutex_unlock(&kprobe_blacklist_mutex);
> +}
> +
>  /* Module notifier call back, checking kprobes on the module */
>  static int kprobes_module_callback(struct notifier_block *nb,
>  				   unsigned long val, void *data)
> @@ -2092,6 +2120,16 @@ static int kprobes_module_callback(struct notifier_block *nb,
>  	unsigned int i;
>  	int checkcore = (val == MODULE_STATE_GOING);
>  
> +	/* Add/remove module blacklist */
> +	if (val == MODULE_STATE_COMING)
> +		populate_kprobe_blacklist(mod->kprobe_blacklist,
> +					  mod->kprobe_blacklist +
> +					  mod->num_kprobe_blacklist);
> +	else if (val == MODULE_STATE_GOING)
> +		shrink_kprobe_blacklist(mod->kprobe_blacklist,
> +					mod->kprobe_blacklist +
> +					mod->num_kprobe_blacklist);
> +
>  	if (val != MODULE_STATE_GOING && val != MODULE_STATE_LIVE)
>  		return NOTIFY_DONE;
>  
> @@ -2278,6 +2316,7 @@ static const struct file_operations debugfs_kprobes_operations = {
>  /* kprobes/blacklist -- shows which functions can not be probed */
>  static void *kprobe_blacklist_seq_start(struct seq_file *m, loff_t *pos)
>  {
> +	mutex_lock(&kprobe_blacklist_mutex);
>  	return seq_list_start(&kprobe_blacklist, *pos);
>  }
>  
> @@ -2286,6 +2325,11 @@ static void *kprobe_blacklist_seq_next(struct seq_file *m, void *v, loff_t *pos)
>  	return seq_list_next(v, &kprobe_blacklist, pos);
>  }
>  
> +static void kprobe_blacklist_seq_stop(struct seq_file *m, void *v)
> +{
> +	mutex_unlock(&kprobe_blacklist_mutex);
> +}
> +
>  static int kprobe_blacklist_seq_show(struct seq_file *m, void *v)
>  {
>  	struct kprobe_blacklist_entry *ent =
> @@ -2299,7 +2343,7 @@ static int kprobe_blacklist_seq_show(struct seq_file *m, void *v)
>  static const struct seq_operations kprobe_blacklist_seq_ops = {
>  	.start = kprobe_blacklist_seq_start,
>  	.next  = kprobe_blacklist_seq_next,
> -	.stop  = kprobe_seq_stop,	/* Reuse void function */
> +	.stop  = kprobe_blacklist_seq_stop,
>  	.show  = kprobe_blacklist_seq_show,
>  };
>  
> diff --git a/kernel/module.c b/kernel/module.c
> index 4d2b82e..c3a593c 100644
> --- a/kernel/module.c
> +++ b/kernel/module.c
> @@ -57,6 +57,7 @@
>  #include <linux/percpu.h>
>  #include <linux/kmemleak.h>
>  #include <linux/jump_label.h>
> +#include <linux/kprobes.h>
>  #include <linux/pfn.h>
>  #include <linux/bsearch.h>
>  #include <uapi/linux/module.h>
> @@ -2937,6 +2938,11 @@ static int find_module_sections(struct module *mod, struct load_info *info)
>  					     sizeof(*mod->ftrace_callsites),
>  					     &mod->num_ftrace_callsites);
>  #endif
> +#ifdef CONFIG_KPROBES
> +	mod->kprobe_blacklist = section_objs(info, "_kprobe_blacklist",
> +					     sizeof(*mod->kprobe_blacklist),
> +					     &mod->num_kprobe_blacklist);
> +#endif
>  
>  	mod->extable = section_objs(info, "__ex_table",
>  				    sizeof(*mod->extable), &mod->num_exentries);
>
> --
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