netdev - [PATCH v2 bpf-next 0/4] bpf: Introduce kptr

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Date:   Wed, 22 Feb 2023 19:07:13 -0800
From:   Alexei Starovoitov <alexei.starovoitov@...il.com>
To:     davem@...emloft.net
Cc:     daniel@...earbox.net, andrii@...nel.org, martin.lau@...nel.org,
        void@...ifault.com, davemarchevsky@...a.com, tj@...nel.org,
        memxor@...il.com, netdev@...r.kernel.org, bpf@...r.kernel.org,
        kernel-team@...com
Subject: [PATCH v2 bpf-next 0/4] bpf: Introduce kptr_rcu.

From: Alexei Starovoitov <ast@...nel.org>

v1->v2:
Instead of agressively allow dereferenced kptr_rcu pointers into KF_TRUSTED_ARGS
kfuncs only allow them into KF_RCU funcs.
The KF_RCU flag is a weaker version of KF_TRUSTED_ARGS. The kfuncs marked with
KF_RCU expect either PTR_TRUSTED or MEM_RCU arguments. The verifier guarantees
that the objects are valid and there is no use-after-free, but the pointers
maybe NULL and pointee object's reference count could have reached zero, hence
kfuncs must do != NULL check and consider refcnt==0 case when accessing such
arguments.
No changes in patch 1.
Patches 2,3,4 adjusted with above behavior.

v1:
The __kptr_ref turned out to be too limited, since any "trusted" pointer access
requires bpf_kptr_xchg() which is impractical when the same pointer needs
to be dereferenced by multiple cpus.
The __kptr "untrusted" only access isn't very useful in practice.
Rename __kptr to __kptr_untrusted with eventual goal to deprecate it,
and rename __kptr_ref to __kptr, since that looks to be more common use of kptrs.
Introduce __kptr_rcu that can be directly dereferenced and used similar
to native kernel C code.
Once bpf_cpumask and task_struct kfuncs are converted to observe RCU GP
when refcnt goes to zero, both __kptr and __kptr_untrusted can be deprecated
and __kptr_rcu can become the only __kptr tag.

Alexei Starovoitov (4):
  bpf: Rename __kptr_ref -> __kptr and __kptr -> __kptr_untrusted.
  bpf: Introduce kptr_rcu.
  selftests/bpf: Add a test case for kptr_rcu.
  selftests/bpf: Tweak cgroup kfunc test.

 Documentation/bpf/bpf_design_QA.rst           |  4 +--
 Documentation/bpf/cpumasks.rst                |  4 +--
 Documentation/bpf/kfuncs.rst                  | 13 ++++----
 include/linux/bpf.h                           | 15 ++++++---
 include/linux/btf.h                           |  2 +-
 kernel/bpf/btf.c                              | 26 +++++++++++++--
 kernel/bpf/helpers.c                          |  7 ++--
 kernel/bpf/syscall.c                          |  4 +++
 kernel/bpf/verifier.c                         | 33 ++++++++++++-------
 net/bpf/test_run.c                            |  3 +-
 tools/lib/bpf/bpf_helpers.h                   |  3 +-
 tools/testing/selftests/bpf/progs/cb_refs.c   |  2 +-
 .../selftests/bpf/progs/cgrp_kfunc_common.h   |  2 +-
 .../selftests/bpf/progs/cgrp_kfunc_failure.c  |  2 +-
 .../selftests/bpf/progs/cgrp_kfunc_success.c  |  7 +++-
 .../selftests/bpf/progs/cpumask_common.h      |  2 +-
 .../selftests/bpf/progs/jit_probe_mem.c       |  2 +-
 tools/testing/selftests/bpf/progs/lru_bug.c   |  2 +-
 tools/testing/selftests/bpf/progs/map_kptr.c  | 18 ++++++++--
 .../selftests/bpf/progs/map_kptr_fail.c       |  6 ++--
 .../selftests/bpf/progs/task_kfunc_common.h   |  2 +-
 tools/testing/selftests/bpf/test_verifier.c   | 22 ++++++-------
 tools/testing/selftests/bpf/verifier/calls.c  |  2 +-
 23 files changed, 123 insertions(+), 60 deletions(-)

-- 
2.30.2