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SubjectRe: [PATCH] livepatch: RCU protect struct klp_func all the time when used in klp_ftrace_handler()
On Sat, Feb 21, 2015 at 12:29:30AM +0100, Jiri Kosina wrote:
> On Wed, 18 Feb 2015, Petr Mladek wrote:
>
> > func->new_func has been accessed after rcu_read_unlock() in klp_ftrace_handler()
> > and therefore the access was not protected.
> >
> > Signed-off-by: Petr Mladek <pmladek@suse.cz>
> > ---
> > kernel/livepatch/core.c | 6 +++---
> > 1 file changed, 3 insertions(+), 3 deletions(-)
> >
> > diff --git a/kernel/livepatch/core.c b/kernel/livepatch/core.c
> > index ff7f47d026ac..cde66192e20e 100644
> > --- a/kernel/livepatch/core.c
> > +++ b/kernel/livepatch/core.c
> > @@ -314,12 +314,12 @@ static void notrace klp_ftrace_handler(unsigned long ip,
> > rcu_read_lock();
> > func = list_first_or_null_rcu(&ops->func_stack, struct klp_func,
> > stack_node);
> > - rcu_read_unlock();
> > -
> > if (WARN_ON_ONCE(!func))
> > - return;
> > + goto unlock;
> >
> > klp_arch_set_pc(regs, (unsigned long)func->new_func);
> > +unlock:
> > + rcu_read_unlock();
>
> This can't hurt, even though the only scenario where this could in theory
> trigger as a bug (module removal) is non-issue now.
>
> But I'd like to take it nevertheless ... Seth, Josh?

Acked-by: Josh Poimboeuf <jpoimboe@redhat.com>

--
Josh


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