[bpf-next,v2,0/6] bpf: Support struct argument for trampoline base progs

Message

Yonghong Song Aug. 12, 2022, 5:24 a.m. UTC

Currently struct arguments are not supported for trampoline based progs.
One of major reason is that struct argument may pass by value which may
use more than one registers. This breaks trampoline progs where
each argument is assumed to take one register. bcc community reported the
issue ([1]) where struct argument is not supported for fentry program.
  typedef struct {
        uid_t val;
  } kuid_t;
  typedef struct {
        gid_t val;
  } kgid_t;
  int security_path_chown(struct path *path, kuid_t uid, kgid_t gid);
Inside Meta, we also have a use case to attach to tcp_setsockopt()
  typedef struct {
        union {
                void            *kernel;
                void __user     *user;
        };
        bool            is_kernel : 1;
  } sockptr_t;
  int tcp_setsockopt(struct sock *sk, int level, int optname,
                     sockptr_t optval, unsigned int optlen);

This patch added struct value support for bpf tracing programs which
uses trampoline. For x86_64, struct argument size needs to be 16 or less so
it can fit in one or two registers. struct argument is not supported
for arm64 in this patch set.

 [1] https://github.com/iovisor/bcc/issues/3657

Changelog:
  rfc v1 -> v2:
   - changed bpf_func_model struct info fields to
     arg_flags[] to make it easy to iterate arguments
     in arch specific {save|restore}_regs() functions.
   - added fexit tests to test return values with
     struct arguments.

Yonghong Song (6):
  bpf: Add struct argument info in btf_func_model
  bpf: x86: Rename stack_size to regs_off in {save,restore}_regs()
  bpf: x86: Support in-register struct arguments
  bpf: arm64: No support of struct argument
  bpf: Populate struct argument info in btf_func_model
  selftests/bpf: Add struct argument tests with fentry/fexit programs.

 arch/arm64/net/bpf_jit_comp.c                 |   8 +-
 arch/x86/net/bpf_jit_comp.c                   | 137 ++++++++++++++----
 include/linux/bpf.h                           |   4 +
 kernel/bpf/btf.c                              |  30 +++-
 .../selftests/bpf/bpf_testmod/bpf_testmod.c   |  41 ++++++
 .../selftests/bpf/prog_tests/tracing_struct.c |  55 +++++++
 .../selftests/bpf/progs/tracing_struct.c      |  93 ++++++++++++
 7 files changed, 334 insertions(+), 34 deletions(-)
 create mode 100644 tools/testing/selftests/bpf/prog_tests/tracing_struct.c
 create mode 100644 tools/testing/selftests/bpf/progs/tracing_struct.c