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

[Masami Hiramatsu]

On Fri, 7 Dec 2018 18:00:26 +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.
> > 
> > Reported-by: Andrea Righi <righi.andrea@xxxxxxxxx>
> > Signed-off-by: Masami Hiramatsu <mhiramat@xxxxxxxxxx>
> > ---
> 
> [snip]
> 
> > +int kprobe_add_ksym_blacklist(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 - offset;
> > +	ent->end_addr = entry - offset + size;
> 
> Do we need to take offset into account? The code before wasn't using it.

Yes, if we hit an alias symbol (zero-size), we forcibly increment address
and retry it. In that case, offset will be 1.

> 
> > +	INIT_LIST_HEAD(&ent->list);
> > +	list_add_tail(&ent->list, &kprobe_blacklist);
> > +
> > +	return (int)size;
> > +}
> > +
> > +/* Add functions in arch defined probe-prohibited area */
> > +int __weak arch_populate_kprobe_blacklist(void)
> > +{
> > +	unsigned long entry;
> > +	int ret = 0;
> > +
> > +	for (entry = (unsigned long)__kprobes_text_start;
> > +	     entry < (unsigned long)__kprobes_text_end;
> > +	     entry += ret) {
> > +		ret = kprobe_add_ksym_blacklist(entry);
> > +		if (ret < 0)
> > +			return ret;
> > +		if (ret == 0)	/* In case of alias symbol */
> > +			ret = 1;

Here, we incremented.

Thank you,

> > +	}
> > +	return 0;
> > +}
> > +
> >  /*
> >   * Lookup and populate the kprobe_blacklist.
> >   *
> > @@ -2104,26 +2142,20 @@ NOKPROBE_SYMBOL(dump_kprobe);
> >  static int __init populate_kprobe_blacklist(unsigned long *start,
> >  					     unsigned long *end)
> >  {
> > +	unsigned long entry;
> >  	unsigned long *iter;
> > -	struct kprobe_blacklist_entry *ent;
> > -	unsigned long entry, offset = 0, size = 0;
> > +	int ret;
> >  
> >  	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_add_ksym_blacklist(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;
> > +
> > +	return arch_populate_kprobe_blacklist();
> >  }
> >  
> >  /* Module notifier call back, checking kprobes on the module */


-- 
Masami Hiramatsu <mhiramat@xxxxxxxxxx>