mbox series

[bpf-next,v6,0/3] bpf, x86: allow function arguments up to 12 for TRACING

Message ID 20230619114947.1543848-1-imagedong@tencent.com
Headers
Series bpf, x86: allow function arguments up to 12 for TRACING |

Message

Menglong Dong June 19, 2023, 11:49 a.m. UTC 
  From: Menglong Dong <imagedong@tencent.com>

For now, the BPF program of type BPF_PROG_TYPE_TRACING can only be used
on the kernel functions whose arguments count less than 6. This is not
friendly at all, as too many functions have arguments count more than 6.
According to the current kernel version, below is a statistics of the
function arguments count:

argument count | function count
7              | 704
8              | 270
9              | 84
10             | 47
11             | 47
12             | 27
13             | 22
14             | 5
15             | 0
16             | 1

Therefore, let's enhance it by increasing the function arguments count
allowed in arch_prepare_bpf_trampoline(), for now, only x86_64.

In the 1st patch, we save/restore regs with BPF_DW size to make the code
in save_regs()/restore_regs() simpler.

In the 2nd patch, we make arch_prepare_bpf_trampoline() support to copy
function arguments in stack for x86 arch. Therefore, the maximum
arguments can be up to MAX_BPF_FUNC_ARGS for FENTRY and FEXIT. Meanwhile,
we clean the potentian garbage value when we copy the arguments on-stack.

And the 3rd patches are for the testcases of the this series.

Changes since v5:
- adjust the commit log of the 1st patch, avoiding confusing people that
  bugs exist in current code
- introduce get_nr_regs() to get the space that used to pass args on
  stack correct in the 2nd patch
- add testcases to tracing_struct.c instead of fentry_test.c and
  fexit_test.c

Changes since v4:
- consider the case of the struct in arguments can't be hold by regs
- add comment for some code
- add testcases for MODIFY_RETURN
- rebase to the latest

Changes since v3:
- try make the stack pointer 16-byte aligned. Not sure if I'm right :)
- introduce clean_garbage() to clean the grabage when argument count is 7
- use different data type in bpf_testmod_fentry_test{7,12}
- add testcase for grabage values in ctx

Changes since v2:
- keep MAX_BPF_FUNC_ARGS still
- clean garbage value in upper bytes in the 2nd patch
- move bpf_fentry_test{7,12} to bpf_testmod.c and rename them to
  bpf_testmod_fentry_test{7,12} meanwhile in the 3rd patch

Changes since v1:
- change the maximun function arguments to 14 from 12
- add testcases (Jiri Olsa)
- instead EMIT4 with EMIT3_off32 for "lea" to prevent overflow

Menglong Dong (3):
  bpf, x86: save/restore regs with BPF_DW size
  bpf, x86: allow function arguments up to 12 for TRACING
  selftests/bpf: add testcase for TRACING with 6+ arguments

 arch/x86/net/bpf_jit_comp.c                   | 249 +++++++++++++++---
 net/bpf/test_run.c                            |  23 +-
 .../selftests/bpf/bpf_testmod/bpf_testmod.c   |  49 +++-
 .../selftests/bpf/prog_tests/fentry_fexit.c   |   4 +-
 .../selftests/bpf/prog_tests/fentry_test.c    |   2 +
 .../selftests/bpf/prog_tests/fexit_test.c     |   2 +
 .../selftests/bpf/prog_tests/modify_return.c  |  20 +-
 .../selftests/bpf/prog_tests/tracing_struct.c |  19 ++
 .../testing/selftests/bpf/progs/fentry_test.c |  32 +++
 .../testing/selftests/bpf/progs/fexit_test.c  |  33 +++
 .../selftests/bpf/progs/modify_return.c       |  40 +++
 .../selftests/bpf/progs/tracing_struct.c      |  48 ++++
 12 files changed, 471 insertions(+), 50 deletions(-)

Comments

Yonghong Song June 21, 2023, 4:07 p.m. UTC | #1 
On 6/19/23 4:49 AM, menglong8.dong@gmail.com wrote:
> From: Menglong Dong <imagedong@tencent.com>
> 
> For now, the BPF program of type BPF_PROG_TYPE_TRACING can only be used
> on the kernel functions whose arguments count less than 6. This is not

less than or equal to 6, if not considering '> 8 bytes'
struct arguments.

> friendly at all, as too many functions have arguments count more than 6.
> According to the current kernel version, below is a statistics of the
> function arguments count:
> 
> argument count | function count
> 7              | 704
> 8              | 270
> 9              | 84
> 10             | 47
> 11             | 47
> 12             | 27
> 13             | 22
> 14             | 5
> 15             | 0
> 16             | 1
> 
> Therefore, let's enhance it by increasing the function arguments count
> allowed in arch_prepare_bpf_trampoline(), for now, only x86_64.
> 
> In the 1st patch, we save/restore regs with BPF_DW size to make the code
> in save_regs()/restore_regs() simpler.
> 
> In the 2nd patch, we make arch_prepare_bpf_trampoline() support to copy
> function arguments in stack for x86 arch. Therefore, the maximum
> arguments can be up to MAX_BPF_FUNC_ARGS for FENTRY and FEXIT.

for FENTRY, FEXIT and MODIFY_RETURN.

  Meanwhile,
> we clean the potentian garbage value when we copy the arguments on-stack.

potentian -> potential

> 
> And the 3rd patches are for the testcases of the this series.

the 3rd patch is ...

> 
> Changes since v5:
> - adjust the commit log of the 1st patch, avoiding confusing people that
>    bugs exist in current code
> - introduce get_nr_regs() to get the space that used to pass args on
>    stack correct in the 2nd patch
> - add testcases to tracing_struct.c instead of fentry_test.c and
>    fexit_test.c
> 
> Changes since v4:
> - consider the case of the struct in arguments can't be hold by regs
> - add comment for some code
> - add testcases for MODIFY_RETURN
> - rebase to the latest
> 
> Changes since v3:
> - try make the stack pointer 16-byte aligned. Not sure if I'm right :)
> - introduce clean_garbage() to clean the grabage when argument count is 7
> - use different data type in bpf_testmod_fentry_test{7,12}
> - add testcase for grabage values in ctx
> 
> Changes since v2:
> - keep MAX_BPF_FUNC_ARGS still
> - clean garbage value in upper bytes in the 2nd patch
> - move bpf_fentry_test{7,12} to bpf_testmod.c and rename them to
>    bpf_testmod_fentry_test{7,12} meanwhile in the 3rd patch
> 
> Changes since v1:
> - change the maximun function arguments to 14 from 12
> - add testcases (Jiri Olsa)
> - instead EMIT4 with EMIT3_off32 for "lea" to prevent overflow
> 
> Menglong Dong (3):
>    bpf, x86: save/restore regs with BPF_DW size
>    bpf, x86: allow function arguments up to 12 for TRACING
>    selftests/bpf: add testcase for TRACING with 6+ arguments
> 
>   arch/x86/net/bpf_jit_comp.c                   | 249 +++++++++++++++---
>   net/bpf/test_run.c                            |  23 +-
>   .../selftests/bpf/bpf_testmod/bpf_testmod.c   |  49 +++-
>   .../selftests/bpf/prog_tests/fentry_fexit.c   |   4 +-
>   .../selftests/bpf/prog_tests/fentry_test.c    |   2 +
>   .../selftests/bpf/prog_tests/fexit_test.c     |   2 +
>   .../selftests/bpf/prog_tests/modify_return.c  |  20 +-
>   .../selftests/bpf/prog_tests/tracing_struct.c |  19 ++
>   .../testing/selftests/bpf/progs/fentry_test.c |  32 +++
>   .../testing/selftests/bpf/progs/fexit_test.c  |  33 +++
>   .../selftests/bpf/progs/modify_return.c       |  40 +++
>   .../selftests/bpf/progs/tracing_struct.c      |  48 ++++
>   12 files changed, 471 insertions(+), 50 deletions(-)
>