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From: Florent Revest <revest@chromium.org>
To: bpf@vger.kernel.org
Cc: ast@kernel.org, daniel@iogearbox.net, andrii@kernel.org,
	yhs@fb.com, kpsingh@kernel.org, jackmanb@chromium.org,
	linux-kernel@vger.kernel.org,
	Florent Revest <revest@chromium.org>
Subject: [PATCH bpf-next v5 0/6] Add a snprintf eBPF helper
Date: Mon, 19 Apr 2021 17:52:37 +0200	[thread overview]
Message-ID: <20210419155243.1632274-1-revest@chromium.org> (raw)

We have a usecase where we want to audit symbol names (if available) in
callback registration hooks. (ex: fentry/nf_register_net_hook)

A few months back, I proposed a bpf_kallsyms_lookup series but it was
decided in the reviews that a more generic helper, bpf_snprintf, would
be more useful.

This series implements the helper according to the feedback received in
https://lore.kernel.org/bpf/20201126165748.1748417-1-revest@google.com/T/#u

- A new arg type guarantees the NULL-termination of string arguments and
  lets us pass format strings in only one arg
- A new helper is implemented using that guarantee. Because the format
  string is known at verification time, the format string validation is
  done by the verifier
- To implement a series of tests for bpf_snprintf, the logic for
  marshalling variadic args in a fixed-size array is reworked as per:
https://lore.kernel.org/bpf/20210310015455.1095207-1-revest@chromium.org/T/#u

---
Changes in v5:
- Fixed the bpf_printf_buf_used counter logic in try_get_fmt_tmp_buf
- Added a couple of extra incorrect specifiers tests
- Call test_snprintf_single__destroy unconditionally
- Fixed a C++-style comment

---
Changes in v4:
- Moved bpf_snprintf, bpf_printf_prepare and bpf_printf_cleanup to
  kernel/bpf/helpers.c so that they get built without CONFIG_BPF_EVENTS
- Added negative test cases (various invalid format strings)
- Renamed put_fmt_tmp_buf() as bpf_printf_cleanup()
- Fixed a mistake that caused temporary buffers to be unconditionally
  freed in bpf_printf_prepare
- Fixed a mistake that caused missing 0 character to be ignored
- Fixed a warning about integer to pointer conversion
- Misc cleanups

---
Changes in v3:
- Simplified temporary buffer acquisition with try_get_fmt_tmp_buf()
- Made zero-termination check more consistent
- Allowed NULL output_buffer
- Simplified the BPF_CAST_FMT_ARG macro
- Three new test cases: number padding, simple string with no arg and
  string length extraction only with a NULL output buffer
- Clarified helper's description for edge cases (eg: str_size == 0)
- Lots of cosmetic changes

---
Changes in v2:
- Extracted the format validation/argument sanitization in a generic way
  for all printf-like helpers.
- bpf_snprintf's str_size can now be 0
- bpf_snprintf is now exposed to all BPF program types
- We now preempt_disable when using a per-cpu temporary buffer
- Addressed a few cosmetic changes

Florent Revest (6):
  bpf: Factorize bpf_trace_printk and bpf_seq_printf
  bpf: Add a ARG_PTR_TO_CONST_STR argument type
  bpf: Add a bpf_snprintf helper
  libbpf: Initialize the bpf_seq_printf parameters array field by field
  libbpf: Introduce a BPF_SNPRINTF helper macro
  selftests/bpf: Add a series of tests for bpf_snprintf

 include/linux/bpf.h                           |  22 ++
 include/uapi/linux/bpf.h                      |  28 ++
 kernel/bpf/helpers.c                          | 306 ++++++++++++++
 kernel/bpf/verifier.c                         |  82 ++++
 kernel/trace/bpf_trace.c                      | 373 ++----------------
 tools/include/uapi/linux/bpf.h                |  28 ++
 tools/lib/bpf/bpf_tracing.h                   |  58 ++-
 .../selftests/bpf/prog_tests/snprintf.c       | 125 ++++++
 .../selftests/bpf/progs/test_snprintf.c       |  73 ++++
 .../bpf/progs/test_snprintf_single.c          |  20 +
 10 files changed, 770 insertions(+), 345 deletions(-)
 create mode 100644 tools/testing/selftests/bpf/prog_tests/snprintf.c
 create mode 100644 tools/testing/selftests/bpf/progs/test_snprintf.c
 create mode 100644 tools/testing/selftests/bpf/progs/test_snprintf_single.c

-- 
2.31.1.368.gbe11c130af-goog


             reply	other threads:[~2021-04-19 15:52 UTC|newest]

Thread overview: 23+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-04-19 15:52 Florent Revest [this message]
2021-04-19 15:52 ` [PATCH bpf-next v5 1/6] bpf: Factorize bpf_trace_printk and bpf_seq_printf Florent Revest
2021-04-19 15:52 ` [PATCH bpf-next v5 2/6] bpf: Add a ARG_PTR_TO_CONST_STR argument type Florent Revest
2021-04-19 22:54   ` Alexei Starovoitov
2021-04-20 12:35     ` Florent Revest
2021-04-20 15:23       ` Alexei Starovoitov
2021-04-22  8:41         ` Florent Revest
2021-04-19 15:52 ` [PATCH bpf-next v5 3/6] bpf: Add a bpf_snprintf helper Florent Revest
2021-04-19 15:52 ` [PATCH bpf-next v5 4/6] libbpf: Initialize the bpf_seq_printf parameters array field by field Florent Revest
2021-04-19 15:52 ` [PATCH bpf-next v5 5/6] libbpf: Introduce a BPF_SNPRINTF helper macro Florent Revest
2021-04-19 15:52 ` [PATCH bpf-next v5 6/6] selftests/bpf: Add a series of tests for bpf_snprintf Florent Revest
2021-04-23 22:38   ` Andrii Nakryiko
2021-04-26 10:10     ` Florent Revest
2021-04-26 16:19       ` Andrii Nakryiko
2021-04-26 21:08         ` Florent Revest
2021-04-27  6:35           ` Rasmus Villemoes
2021-04-27  9:50             ` Florent Revest
2021-04-27 18:03               ` Andrii Nakryiko
2021-04-28 14:59                 ` Florent Revest
2021-05-05  6:55                   ` Rasmus Villemoes
2021-05-05 14:25                     ` Florent Revest
2021-04-19 19:33 ` [PATCH bpf-next v5 0/6] Add a snprintf eBPF helper Andrii Nakryiko
2021-04-20 12:02   ` Florent Revest

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