[bpf-next,v2,0/5] Extend struct_ops support for operators

Message

Amery Hung Feb. 17, 2025, 7:06 p.m. UTC

Hi,

This patchset supports struct_ops operators that acquire kptrs through
arguments and operators that return a kptr. A coming new struct_ops use
case, bpf qdisc [0], has two operators that are not yet supported by
current struct_ops infrastructure. Qdisc_ops::enqueue requires getting
referenced skb kptr from the argument; Qdisc_ops::dequeue needs to return
a referenced skb kptr. This patchset will allow bpf qdisc and other
potential struct_ops implementers to do so.

For struct_ops implementers:

- To get a kptr from an argument, a struct_ops implementer needs to
  annotate the argument name in the stub function with "__ref" suffix.

- The kptr return will automatically work as we now allow operators that
  return a struct pointer.

- The verifier allows returning a null pointer. More control can be
  added later if there is a future struct_ops implementer only expecting
  valid pointers.

For struct_ops users:

- The referenced kptr acquired through the argument needs to be released
  or xchged into maps just like ones acquired via kfuncs.

- To return a referenced kptr in struct_ops,
  1) The type of the pointer must matches the return type
  2) The pointer must comes from the kernel (not locally allocated), and
  3) The pointer must be in its unmodified form


[0] https://lore.kernel.org/bpf/[e-mail]/

---
v2
- Replace kcalloc+memcpy with kmemdup_array in
  bpf_prog_ctx_arg_info_init() 
- Remove unnecessary checks when kfree-ing ctx_arg_info
- Remove conditional assignment of ref_obj_id in btf_ctx_access()

v1
- Link: https://lore.kernel.org/bpf/[e-mail]/
- Fix missing kfree for ctx_arg_info

Amery Hung (5):
  bpf: Make every prog keep a copy of ctx_arg_info
  bpf: Support getting referenced kptr from struct_ops argument
  selftests/bpf: Test referenced kptr arguments of struct_ops programs
  bpf: Allow struct_ops prog to return referenced kptr
  selftests/bpf: Test returning referenced kptr from struct_ops programs

 include/linux/bpf.h                           | 10 +-
 kernel/bpf/bpf_iter.c                         | 13 ++-
 kernel/bpf/bpf_struct_ops.c                   | 39 ++++++--
 kernel/bpf/btf.c                              |  1 +
 kernel/bpf/syscall.c                          |  1 +
 kernel/bpf/verifier.c                         | 93 +++++++++++++++----
 .../prog_tests/test_struct_ops_kptr_return.c  | 16 ++++
 .../prog_tests/test_struct_ops_refcounted.c   | 12 +++
 .../bpf/progs/struct_ops_kptr_return.c        | 30 ++++++
 ...uct_ops_kptr_return_fail__invalid_scalar.c | 26 ++++++
 .../struct_ops_kptr_return_fail__local_kptr.c | 34 +++++++
 ...uct_ops_kptr_return_fail__nonzero_offset.c | 25 +++++
 .../struct_ops_kptr_return_fail__wrong_type.c | 30 ++++++
 .../bpf/progs/struct_ops_refcounted.c         | 31 +++++++
 ...ruct_ops_refcounted_fail__global_subprog.c | 39 ++++++++
 .../struct_ops_refcounted_fail__ref_leak.c    | 22 +++++
 .../selftests/bpf/test_kmods/bpf_testmod.c    | 15 +++
 .../selftests/bpf/test_kmods/bpf_testmod.h    |  6 ++
 18 files changed, 410 insertions(+), 33 deletions(-)
 create mode 100644 tools/testing/selftests/bpf/prog_tests/test_struct_ops_kptr_return.c
 create mode 100644 tools/testing/selftests/bpf/prog_tests/test_struct_ops_refcounted.c
 create mode 100644 tools/testing/selftests/bpf/progs/struct_ops_kptr_return.c
 create mode 100644 tools/testing/selftests/bpf/progs/struct_ops_kptr_return_fail__invalid_scalar.c
 create mode 100644 tools/testing/selftests/bpf/progs/struct_ops_kptr_return_fail__local_kptr.c
 create mode 100644 tools/testing/selftests/bpf/progs/struct_ops_kptr_return_fail__nonzero_offset.c
 create mode 100644 tools/testing/selftests/bpf/progs/struct_ops_kptr_return_fail__wrong_type.c
 create mode 100644 tools/testing/selftests/bpf/progs/struct_ops_refcounted.c
 create mode 100644 tools/testing/selftests/bpf/progs/struct_ops_refcounted_fail__global_subprog.c
 create mode 100644 tools/testing/selftests/bpf/progs/struct_ops_refcounted_fail__ref_leak.c

Comments

[e-mail] Feb. 18, 2025, 3 a.m. UTC | #1

Hello:

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

On Mon, 17 Feb 2025 11:06:35 -0800 you wrote:
> Hi,
> 
> This patchset supports struct_ops operators that acquire kptrs through
> arguments and operators that return a kptr. A coming new struct_ops use
> case, bpf qdisc [0], has two operators that are not yet supported by
> current struct_ops infrastructure. Qdisc_ops::enqueue requires getting
> referenced skb kptr from the argument; Qdisc_ops::dequeue needs to return
> a referenced skb kptr. This patchset will allow bpf qdisc and other
> potential struct_ops implementers to do so.
> 
> [...]

Here is the summary with links:
  - [bpf-next,v2,1/5] bpf: Make every prog keep a copy of ctx_arg_info
    https://git.kernel.org/bpf/bpf-next/c/432051806f61
  - [bpf-next,v2,2/5] bpf: Support getting referenced kptr from struct_ops argument
    https://git.kernel.org/bpf/bpf-next/c/a687df2008f6
  - [bpf-next,v2,3/5] selftests/bpf: Test referenced kptr arguments of struct_ops programs
    https://git.kernel.org/bpf/bpf-next/c/6991ec6beb26
  - [bpf-next,v2,4/5] bpf: Allow struct_ops prog to return referenced kptr
    https://git.kernel.org/bpf/bpf-next/c/8d9f547f74c7
  - [bpf-next,v2,5/5] selftests/bpf: Test returning referenced kptr from struct_ops programs
    https://git.kernel.org/bpf/bpf-next/c/af17bad9fb2a

You are awesome, thank you!