Re: [PATCH] kptr_restrict for hiding kernel pointers from unprivileged users

Peter Zijlstra
2010-12-10T16:05:39Z

On Thu, 2010-12-09 at 04:23 +0100, Eric Dumazet wrote:
> > + if (kptr_restrict) {
> > + if (in_interrupt())
> > + WARN(1, "%%pK used in interrupt context.\n");
>
> So caller can not block BH ?
>
> This seems wrong to me, please consider :
>
> normal process context :
>
> spin_lock_bh() ...
>
> for (...)
> {xxx}printf( ... "%pK" ...)
>
> spin_unlock_bh();

That's a bug in in_interrupt(), one I've been pointing out for a long
while. Luckily we recently grew the infrastructure to deal with it.

If you write it as: if (in_irq() || in_serving_softirq() || in_nmi())
you'll not trigger for the above example.

Ideally in_serving_softirq() wouldn't exist and in_softirq() would do
what in_server_softirq() does -- which would make it symmetric with the
hardirq functions -- but nobody has found time to audit all in_softirq()
users.