[PATCH bpf-next 0/8] PTR_TO_BTF_ID arguments in global subprogs

[Andrii Nakryiko <andrii@kernel.org>]

This patch set follows recent changes that added btf_decl_tag-based argument
annotation support for global subprogs. This time we add ability to pass
PTR_TO_BTF_ID (BTF-aware kernel pointers) arguments into global subprograms.
We support explicitly trusted and untrusted arguments. Legacy semi-trusted
variant is not supported.

Patches #2 through #4 do preparatory refactorings to add support for multiple
tags per argument. This is important for being able to use modifiers like
__arg_nonnull together with trusted/untrusted arguments.

Patch #5 is adding the actual __arg_trusted and __arg_untrusted support.

It also raises a question about default nullable vs non-nullable semantics for
PTR_TO_BTF_ID arguments. It feels like having both __arg_nonnull and
__arg_nullable would provide the best kind of experience and flexibility, but
for now we implement nullable by default semantics, as a more conservative
behavior.

Patch #7 adds bpf_core_cast() helper macro which is a wrapper around
bpf_rdonly_cast() kfunc, but hides BTF ID manipulations behind more
user-friendly type argument instead. We utilize this macro in selftests added
in patch #8.

Patch #8 adds a bunch of positive and negative tests to validate expected
semantics for various trusted/untrusted + nullable/non-null variants. We also
make sure that global subprog cannot destroy PTR_TO_BTF_ID, as that would
wreak havoc in caller program that is not aware of this possibility.

There were proposals to do kernel-side type enforcement for __arg_ctx, let's
decide whether we should do that and for which program types, and I can
accommodate the logic in future revisions.

Cc: Dave Marchevsky <davemarchevsky@meta.com>

Andrii Nakryiko (8):
  selftests/bpf: fix test_loader check message
  bpf: make sure scalar args don't accept __arg_nonnull tag
  bpf: prepare btf_prepare_func_args() for multiple tags per argument
  bpf: support multiple tags per argument
  bpf: add __arg_trusted and __arg_untrusted global func tags
  libbpf: add __arg_trusted and __arg_untrusted annotation macros
  libbpf: add bpf_core_cast() macro
  selftests/bpf: add trusted/untrusted global subprog arg tests

 include/linux/bpf.h                           |   2 +
 include/linux/bpf_verifier.h                  |   1 +
 kernel/bpf/btf.c                              | 228 +++++++++++++-----
 kernel/bpf/verifier.c                         |  32 ++-
 tools/lib/bpf/bpf_core_read.h                 |  13 +
 tools/lib/bpf/bpf_helpers.h                   |   2 +
 tools/testing/selftests/bpf/bpf_kfuncs.h      |   2 +-
 .../selftests/bpf/prog_tests/verifier.c       |   2 +
 .../bpf/progs/nested_trust_failure.c          |   2 +-
 .../bpf/progs/sk_storage_omem_uncharge.c      |   2 -
 tools/testing/selftests/bpf/progs/type_cast.c |   4 +-
 .../bpf/progs/verifier_global_ptr_args.c      | 160 ++++++++++++
 tools/testing/selftests/bpf/test_loader.c     |   2 +-
 13 files changed, 387 insertions(+), 65 deletions(-)
 create mode 100644 tools/testing/selftests/bpf/progs/verifier_global_ptr_args.c

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2.34.1