Re: [PATCH] kprobes: x86_64: blacklist non-attachable interrupt functions

[Masami Hiramatsu]

On Fri, 7 Dec 2018 18:58:05 +0100
Andrea Righi <righi.andrea@xxxxxxxxx> wrote:

> On Sat, Dec 08, 2018 at 01:01:20AM +0900, Masami Hiramatsu wrote:
> > Hi Andrea and Ingo,
> > 
> > Here is the patch what I meant. I just ran it on qemu-x86, and seemed working.
> > After introducing this patch, I will start adding arch_populate_kprobe_blacklist()
> > to some arches.
> > 
> > Thank you,
> > 
> > [RFC] kprobes: x86/kprobes: Blacklist symbols in arch-defined prohibited area
> > 
> > From: Masami Hiramatsu <mhiramat@xxxxxxxxxx>
> > 
> > Blacklist symbols in arch-defined probe-prohibited areas.
> > With this change, user can see all symbols which are prohibited
> > to probe in debugfs.
> > 
> > All archtectures which have custom prohibit areas should define
> > its own arch_populate_kprobe_blacklist() function, but unless that,
> > all symbols marked __kprobes are blacklisted.
> 
> What about iterating all symbols and use arch_within_kprobe_blacklist()
> to check if we need to blacklist them or not.

Sorry, I don't want to iterate all ksyms since it may take a long time
(especially embedded small devices.)

> 
> In this way we don't have to introduce an
> arch_populate_kprobe_blacklist() for each architecture.

Hmm, I had a same idea, but there are some arch which prohibit probing
extable entries (e.g. arm64.) For correctness of the blacklist, I think
it should be listed (not entire the function body).
I also rather like to remove arch_within_kprobe_blacklist() instead.

Thank you,

> 
> Something like the following maybe.
> 
> Thanks.
> 
> [RFC] kprobes: blacklist all symbols in arch-defined prohibited area
> 
> From: Andrea Righi <righi.andrea@xxxxxxxxx>
> 
> Blacklist symbols in arch-defined probe-prohibited areas.
> With this change, user can see all symbols which are prohibited
> to probe in debugfs.
> 
> Signed-off-by: Masami Hiramatsu <mhiramat@xxxxxxxxxx>
> Signed-off-by: Andrea Righi <righi.andrea@xxxxxxxxx>
> ---
>  kernel/kprobes.c | 55 +++++++++++++++++++++++++++++++++++++++++--------------
>  1 file changed, 41 insertions(+), 14 deletions(-)
> 
> diff --git a/kernel/kprobes.c b/kernel/kprobes.c
> index 90e98e233647..e67598dd7468 100644
> --- a/kernel/kprobes.c
> +++ b/kernel/kprobes.c
> @@ -2093,6 +2093,35 @@ void dump_kprobe(struct kprobe *kp)
>  }
>  NOKPROBE_SYMBOL(dump_kprobe);
>  
> +static int kprobe_blacklist_add(unsigned long entry)
> +{
> +	struct kprobe_blacklist_entry *ent;
> +	unsigned long offset = 0, size = 0;
> +
> +	if (!kernel_text_address(entry) ||
> +	    !kallsyms_lookup_size_offset(entry, &size, &offset))
> +		return -EINVAL;
> +
> +	ent = kmalloc(sizeof(*ent), GFP_KERNEL);
> +	if (!ent)
> +		return -ENOMEM;
> +	ent->start_addr = entry;
> +	ent->end_addr = entry + size;
> +	INIT_LIST_HEAD(&ent->list);
> +	list_add_tail(&ent->list, &kprobe_blacklist);
> +
> +	return 0;
> +}
> +
> +static int arch_populate_kprobe_blacklist(void *data, const char *name,
> +					  struct module *mod,
> +					  unsigned long entry)
> +{
> +	if (arch_within_kprobe_blacklist(entry))
> +		kprobe_blacklist_add(entry);
> +	return 0;
> +}
> +
>  /*
>   * Lookup and populate the kprobe_blacklist.
>   *
> @@ -2104,24 +2133,22 @@ NOKPROBE_SYMBOL(dump_kprobe);
>  static int __init populate_kprobe_blacklist(unsigned long *start,
>  					     unsigned long *end)
>  {
> -	unsigned long *iter;
> -	struct kprobe_blacklist_entry *ent;
> -	unsigned long entry, offset = 0, size = 0;
> +	unsigned long entry, *iter;
> +	int ret;
>  
> +	/* Blacklist all arch_within_kprobe_blacklist() symbols */
> +        mutex_lock(&module_mutex);
> +	kallsyms_on_each_symbol(arch_populate_kprobe_blacklist, NULL);
> +        mutex_unlock(&module_mutex);
> +
> +	/* Add explicitly blacklisted symbols */
>  	for (iter = start; iter < end; iter++) {
>  		entry = arch_deref_entry_point((void *)*iter);
> -
> -		if (!kernel_text_address(entry) ||
> -		    !kallsyms_lookup_size_offset(entry, &size, &offset))
> +		ret = kprobe_blacklist_add(entry);
> +		if (ret == -EINVAL)
>  			continue;
> -
> -		ent = kmalloc(sizeof(*ent), GFP_KERNEL);
> -		if (!ent)
> -			return -ENOMEM;
> -		ent->start_addr = entry;
> -		ent->end_addr = entry + size;
> -		INIT_LIST_HEAD(&ent->list);
> -		list_add_tail(&ent->list, &kprobe_blacklist);
> +		if (ret < 0)
> +			return ret;
>  	}
>  	return 0;
>  }


-- 
Masami Hiramatsu <mhiramat@xxxxxxxxxx>