Subject: [PATCH bpf 0/4] bpf: remove __rcu annotations from bpf_prog_array

From: Stanislav Fomichev <[email-masked]>
Date: Wed, 8 May 2019 10:18:41 -0700

Right now we are not using rcu api correctly: we pass __rcu pointers
to bpf_prog_array_xyz routines but don't use rcu_dereference on them
(see bpf_prog_array_delete_safe and bpf_prog_array_copy in particular).
Instead of sprinkling rcu_dereferences, let's just get rid of those
__rcu annotations and move rcu handling to a higher level.

It looks like all those routines are called from the rcu update
side and we can use simple rcu_dereference_protected to get a
reference that is valid as long as we hold a mutex (i.e. no other
updater can change the pointer, no need for rcu read section and
there should not be a use-after-free problem).

To be fair, there is currently no issue with the existing approach
since the calls are mutex-protected, pointer values don't change,
__rcu annotations are ignored. But it's still nice to use proper api.

The series fixes the following sparse warnings:

kernel/bpf/core.c:1876:44: warning: incorrect type in initializer (different address spaces)
kernel/bpf/core.c:1876:44:    expected struct bpf_prog_array_item *item
kernel/bpf/core.c:1876:44:    got struct bpf_prog_array_item [noderef] <asn:4> *
kernel/bpf/core.c:1900:26: warning: incorrect type in assignment (different address spaces)
kernel/bpf/core.c:1900:26:    expected struct bpf_prog_array_item *existing
kernel/bpf/core.c:1900:26:    got struct bpf_prog_array_item [noderef] <asn:4> *
kernel/bpf/core.c:1934:26: warning: incorrect type in assignment (different address spaces)
kernel/bpf/core.c:1934:26:    expected struct bpf_prog_array_item *[assigned] existing
kernel/bpf/core.c:1934:26:    got struct bpf_prog_array_item [noderef] <asn:4> *

Stanislav Fomichev (4):
  bpf: remove __rcu annotations from bpf_prog_array
  bpf: media: properly use bpf_prog_array api
  bpf: cgroup: properly use bpf_prog_array api
  bpf: tracing: properly use bpf_prog_array api

 drivers/media/rc/bpf-lirc.c | 27 +++++++++++++++++----------
 include/linux/bpf-cgroup.h  |  2 +-
 include/linux/bpf.h         | 12 ++++++------
 kernel/bpf/cgroup.c         | 27 +++++++++++++++++----------
 kernel/bpf/core.c           | 31 ++++++++++++-------------------
 kernel/trace/bpf_trace.c    | 18 ++++++++++--------
 6 files changed, 63 insertions(+), 54 deletions(-)

-- 
2.21.0.1020.gf2820cf01a-goog