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

Message

Andrii Nakryiko Jan. 5, 2024, 12:09 a.m. UTC

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 <[e-mail]>

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

Comments

Eduard Zingerman Jan. 7, 2024, 10:22 p.m. UTC | #1

On Thu, 2024-01-04 at 16:09 -0800, Andrii Nakryiko wrote:
> 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 <[e-mail]>

Full patch-set looks good to me.
Acked-by: Eduard Zingerman <[e-mail]>

[e-mail] Jan. 12, 2024, 2:40 a.m. UTC | #2

Hello:

This series was applied to bpf/bpf-next.git (master)
by Alexei Starovoitov <[e-mail]>:

On Thu,  4 Jan 2024 16:09:01 -0800 you wrote:
> 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.
> 
> [...]

Here is the summary with links:
  - [bpf-next,1/8] selftests/bpf: fix test_loader check message
    https://git.kernel.org/bpf/bpf-next/c/7c5f9568564a
  - [bpf-next,2/8] bpf: make sure scalar args don't accept __arg_nonnull tag
    https://git.kernel.org/bpf/bpf-next/c/ca3950495684
  - [bpf-next,3/8] bpf: prepare btf_prepare_func_args() for multiple tags per argument
    https://git.kernel.org/bpf/bpf-next/c/5436740cc03d
  - [bpf-next,4/8] bpf: support multiple tags per argument
    https://git.kernel.org/bpf/bpf-next/c/6a21d4e515f5
  - [bpf-next,5/8] bpf: add __arg_trusted and __arg_untrusted global func tags
    (no matching commit)
  - [bpf-next,6/8] libbpf: add __arg_trusted and __arg_untrusted annotation macros
    (no matching commit)
  - [bpf-next,7/8] libbpf: add bpf_core_cast() macro
    (no matching commit)
  - [bpf-next,8/8] selftests/bpf: add trusted/untrusted global subprog arg tests
    (no matching commit)

You are awesome, thank you!