Re: [PATCH v3 1/2] livepatch: send a fake signal to all blocking tasks

Miroslav Benes
2017-11-03T08:07:00Z

On Thu, 2 Nov 2017, Josh Poimboeuf wrote:

> On Tue, Oct 31, 2017 at 12:48:52PM +0100, Miroslav Benes wrote:
> > diff --git a/kernel/livepatch/core.c b/kernel/livepatch/core.c
> > index bf8c8fd72589..b7c60662baf3 100644
> > --- a/kernel/livepatch/core.c
> > +++ b/kernel/livepatch/core.c
> > @@ -440,6 +440,7 @@ EXPORT_SYMBOL_GPL(klp_enable_patch);
> > * /sys/kernel/livepatch/<patch>
> > * /sys/kernel/livepatch/<patch>/enabled
> > * /sys/kernel/livepatch/<patch>/transition
> > + * /sys/kernel/livepatch/<patch>/signal
> > * /sys/kernel/livepatch/<patch>/
> > * /sys/kernel/livepatch/<patch>/ /<function,sympos>
> > */
> > @@ -514,11 +515,37 @@ static ssize_t transition_show(struct kobject *kobj,
> > patch == klp_transition_patch);
> > }
> >
> > +static ssize_t signal_store(struct kobject *kobj, struct kobj_attribute *attr,
> > + const char *buf, size_t count)
> > +{
> > + int ret;
> > + bool val;
> > +
> > + /*
> > + * klp_mutex lock is not grabbed here intentionally. It is not really
> > + * needed. The race window is harmless and grabbing the lock would only
> > + * hold the action back.
> > + */
> > + if (!klp_transition_patch)
> > + return -EINVAL;
> > +
> > + ret = kstrtobool(buf, &val);
> > + if (ret)
> > + return ret;
> > +
> > + if (val)
> > + klp_force_signals();
> > +
> > + return count;
> > +}
>
> The function still has global functionality even though the sysfs entry
> is now per-patch. So if you do
>
> echo 1 > /sys/kernel/livepatch/patch1/signal
>
> But patch2 is in transition, then it will send signals based on patch2.
> Instead it should probably return an error.
>
> There's a similar issue with force_store().

Bah. I still find having "signal" and "force" in
/sys/kernel/livepatch/<patch>/ a bit odd, but I'll add

struct klp_patch *patch;

patch = container_of(kobj, struct klp_patch, kobj);
/*
...
*/
if (patch != klp_transition_patch)
return -EINVAL;

That should solve it for all cases.

Thanks,
Miroslav