[PATCH bpf-next v2 00/12] bpf: Support by-value struct and __int128 arguments

[Yonghong Song <yonghong.song@linux.dev>]

A global function or a kfunc taking a struct or union by value is rejected
today:

  Arg#1 type STRUCT in tar() is not supported yet.
  Unrecognized R2 type STRUCT

and an __int128 argument is accepted but mis-counted: the compiler passes
it in two registers while the verifier gives it one, so every argument
after it is checked against the wrong register and the program is rejected
for a register its source never names.

The compiler passes such a value in one argument register per eightbyte,
so a value of at most 16 bytes arrives in one or two consecutive
registers. This series teaches the verifier to describe that: sub->args[]
gains one entry per argument slot rather than one per BTF parameter, and
the kfunc argument walk counts slots the same way. A value may only be
composed of scalars, as a pointer would reach the callee as an opaque
scalar, losing the provenance and reference tracking that make it safe to
use. A global function still has no stack arguments, so all of its slots
have to fit in the argument registers.

For a kfunc the two calling conventions have to agree, and they do not
always. Where the BPF convention splits a value between the last argument
register and the stack, x86_64 moves the whole of it to the stack and gives
the register to the argument that follows, while arm64 rounds the
register number up to an even one for a 16-byte aligned value. For stack
arguments, both x86_64 and arm64 will have 16-byte alignment for those
16-byte aligned parameters. Otherwise the alignment will be 8-byte.
This is implemented in x86_64 and arm64 jit.

Patch 1 records the __int128 failure as it stands today, which patch 4
turns into a success. Patches 2 to 4 index the arguments of a global
function by slot and accept a by-value struct and an __int128. Patches 6
and 7 have the same for a kfunc call. Patches 8 and 9 place the arguments
per the kernel calling convention in the x86-64 and arm64 JITs.
Patches 10 to 12 are the tests.

Tested on x86-64 and arm64 with test_progs. The by-value struct tests are
built with clang, as GCC passes an aggregate by invisible reference, and
some of them need __BPF_FEATURE_STACK_ARGUMENT.

Changelog:
  v1 -> v2:
    - v1: https://lore.kernel.org/bpf/20260904050957.3976119-1-yonghong.song@linux.dev/
    - Fix a few issues due to potential out of bound access.
    - Fix a few missed cases for kfunc with '> 8 byte' arguments.
    - Add jit support for x86_64 and arm64. Previously certain functions are rejected,
      and now these functions can succeed.

Yonghong Song (12):
  selftests/bpf: Add a test for an __int128 by-value argument
  bpf: Index global function arguments by argument slot
  bpf: Support by-value struct arguments up to 16 bytes
  bpf: Support __int128 as a by-value function argument
  bpf: Rename bpf_call_summary::num_params to arg_slot_cnt
  bpf: Recognize by-value struct and __int128 kfunc arguments
  bpf: Prepare kfunc arguments for the JIT from an ABI description
  bpf, x86: Move kfunc arguments into the x86-64 calling convention
  bpf, arm64: Move kfunc arguments into the arm64 calling convention
  selftests/bpf: Add C tests for by-value arguments up to 16 bytes
  selftests/bpf: Add inline-asm tests for by-value arguments
  selftests/bpf: Add tests for by-value kfunc arguments

 arch/arm64/net/bpf_jit_comp.c                 |  77 +++++-
 arch/x86/net/bpf_jit_comp.c                   |  73 +++++-
 include/linux/bpf.h                           |   8 +
 include/linux/bpf_verifier.h                  |   3 +-
 include/linux/filter.h                        |  32 +++
 kernel/bpf/btf.c                              |  94 +++++--
 kernel/bpf/core.c                             |  94 +++++++
 kernel/bpf/liveness.c                         |  10 +-
 kernel/bpf/verifier.c                         | 239 +++++++++++++++---
 .../selftests/bpf/prog_tests/aggregate_arg.c  |  11 +
 .../selftests/bpf/prog_tests/verifier.c       |   2 +
 .../selftests/bpf/progs/aggregate_arg_func.c  | 155 ++++++++++++
 .../selftests/bpf/progs/aggregate_arg_kfunc.c | 221 ++++++++++++++++
 .../testing/selftests/bpf/progs/arena_kfunc.c |  16 ++
 .../selftests/bpf/progs/stack_arg_fail.c      |  10 -
 .../selftests/bpf/progs/verifier_int128_arg.c | 196 ++++++++++++++
 .../selftests/bpf/test_kmods/bpf_testmod.c    |  77 ++++++
 .../bpf/test_kmods/bpf_testmod_kfunc.h        |  32 +++
 18 files changed, 1271 insertions(+), 79 deletions(-)
 create mode 100644 tools/testing/selftests/bpf/prog_tests/aggregate_arg.c
 create mode 100644 tools/testing/selftests/bpf/progs/aggregate_arg_func.c
 create mode 100644 tools/testing/selftests/bpf/progs/aggregate_arg_kfunc.c
 create mode 100644 tools/testing/selftests/bpf/progs/verifier_int128_arg.c

-- 
2.53.0-Meta