On Wed, 16 Jan 2019 08:44:52 -0500 Steven Rostedt <rost...@goodmis.org> wrote:
> > [ Cc'ing Masami as he maintains uprobes (we need to add uprobes to > the MAINTAINERS file ] Thanks Steve, I think it is maintained mainly by Srikar and Oleg. Srikar, Oleg, could you update MAINTAINERS file to add UPROBES entry? And ack this change? Thank you, > > -- Steve > > On Wed, 16 Jan 2019 13:20:27 +0200 > Elena Reshetova <elena.reshet...@intel.com> wrote: > > > atomic_t variables are currently used to implement reference > > counters with the following properties: > > - counter is initialized to 1 using atomic_set() > > - a resource is freed upon counter reaching zero > > - once counter reaches zero, its further > > increments aren't allowed > > - counter schema uses basic atomic operations > > (set, inc, inc_not_zero, dec_and_test, etc.) > > > > Such atomic variables should be converted to a newly provided > > refcount_t type and API that prevents accidental counter overflows > > and underflows. This is important since overflows and underflows > > can lead to use-after-free situation and be exploitable. > > > > The variable uprobe.ref is used as pure reference counter. > > Convert it to refcount_t and fix up the operations. > > > > **Important note for maintainers: > > > > Some functions from refcount_t API defined in lib/refcount.c > > have different memory ordering guarantees than their atomic > > counterparts. > > The full comparison can be seen in > > https://lkml.org/lkml/2017/11/15/57 and it is hopefully soon > > in state to be merged to the documentation tree. > > Normally the differences should not matter since refcount_t provides > > enough guarantees to satisfy the refcounting use cases, but in > > some rare cases it might matter. > > Please double check that you don't have some undocumented > > memory guarantees for this variable usage. > > > > For the uprobe.ref it might make a difference > > in following places: > > - put_uprobe(): decrement in refcount_dec_and_test() only > > provides RELEASE ordering and control dependency on success > > vs. fully ordered atomic counterpart > > > > Suggested-by: Kees Cook <keesc...@chromium.org> > > Reviewed-by: David Windsor <dwind...@gmail.com> > > Reviewed-by: Hans Liljestrand <ishkam...@gmail.com> > > Signed-off-by: Elena Reshetova <elena.reshet...@intel.com> > > --- > > kernel/events/uprobes.c | 8 ++++---- > > 1 file changed, 4 insertions(+), 4 deletions(-) > > > > diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c > > index ad415f7..750aece 100644 > > --- a/kernel/events/uprobes.c > > +++ b/kernel/events/uprobes.c > > @@ -66,7 +66,7 @@ static struct percpu_rw_semaphore dup_mmap_sem; > > > > struct uprobe { > > struct rb_node rb_node; /* node in the rb tree */ > > - atomic_t ref; > > + refcount_t ref; > > struct rw_semaphore register_rwsem; > > struct rw_semaphore consumer_rwsem; > > struct list_head pending_list; > > @@ -561,13 +561,13 @@ set_orig_insn(struct arch_uprobe *auprobe, struct > > mm_struct *mm, unsigned long v > > > > static struct uprobe *get_uprobe(struct uprobe *uprobe) > > { > > - atomic_inc(&uprobe->ref); > > + refcount_inc(&uprobe->ref); > > return uprobe; > > } > > > > static void put_uprobe(struct uprobe *uprobe) > > { > > - if (atomic_dec_and_test(&uprobe->ref)) { > > + if (refcount_dec_and_test(&uprobe->ref)) { > > /* > > * If application munmap(exec_vma) before uprobe_unregister() > > * gets called, we don't get a chance to remove uprobe from > > @@ -658,7 +658,7 @@ static struct uprobe *__insert_uprobe(struct uprobe > > *uprobe) > > rb_link_node(&uprobe->rb_node, parent, p); > > rb_insert_color(&uprobe->rb_node, &uprobes_tree); > > /* get access + creation ref */ > > - atomic_set(&uprobe->ref, 2); > > + refcount_set(&uprobe->ref, 2); > > > > return u; > > } > -- Masami Hiramatsu <mhira...@kernel.org>
