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

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Date:   Sat, 8 Dec 2018 08:07:18 +0100
From:   Andrea Righi <righi.andrea@...il.com>
To:     Masami Hiramatsu <mhiramat@...nel.org>
Cc:     "Naveen N. Rao" <naveen.n.rao@...ux.vnet.ibm.com>,
        Anil S Keshavamurthy <anil.s.keshavamurthy@...el.com>,
        "David S. Miller" <davem@...emloft.net>,
        Yonghong Song <yhs@...com>, Andy Lutomirski <luto@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "H. Peter Anvin" <hpa@...or.com>, x86@...nel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] kprobes: x86_64: blacklist non-attachable interrupt
 functions

On Sat, Dec 08, 2018 at 12:42:10PM +0900, Masami Hiramatsu wrote:
> On Fri, 7 Dec 2018 18:00:26 +0100
> Andrea Righi <righi.andrea@...il.com> 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@...nel.org>
> > > 
> > > 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@...il.com>
> > > Signed-off-by: Masami Hiramatsu <mhiramat@...nel.org>
> > > ---
> > 
> > [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,

Makes sense, thanks for the clarification.

-Andrea