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

> > + }
> > + 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@kernel.org>

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