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SubjectRe: [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@gmail.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@kernel.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@gmail.com>
> > > Signed-off-by: Masami Hiramatsu <mhiramat@kernel.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

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