From: Alexei Starovoitov <ast@xxxxxxxxxx> 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
