[PATCH v4 0/6] KFuzzTest: a new kernel fuzzing framework

[Ethan Graham <ethan.w.s.graham@gmail.com>]

This patch series introduces KFuzzTest, a lightweight framework for
creating in-kernel fuzz targets for internal kernel functions.

The primary motivation for KFuzzTest is to simplify the fuzzing of
low-level, relatively stateless functions (e.g., data parsers, format
converters) that are difficult to exercise effectively from the syscall
boundary. It is intended for in-situ fuzzing of kernel code without
requiring that it be built as a separate userspace library or that its
dependencies be stubbed out.

Following feedback from the Linux Plumbers Conference and mailing list
discussions, this version of the framework has been significantly
simplified. It now focuses exclusively on handling raw binary inputs,
removing the complexity of the custom serialization format and DWARF
parsing found in previous iterations.

The core design consists of two main parts:
1. The `FUZZ_TEST_SIMPLE(name)` macro, which allows developers to define
   a fuzz test that accepts a buffer and its length.
2. A simplified debugfs interface that allows userspace fuzzers (or
   simple command-line tools) to pass raw binary blobs directly to the
   target function.

To validate the framework's end-to-end effectiveness, we performed an
experiment by manually introducing an off-by-one buffer over-read into
pkcs7_parse_message, like so:

- ret = asn1_ber_decoder(&pkcs7_decoder, ctx, data, datalen);
+ ret = asn1_ber_decoder(&pkcs7_decoder, ctx, data, datalen + 1);

A syzkaller instance fuzzing the new test_pkcs7_parse_message target
introduced in patch 7 successfully triggered the bug inside of
asn1_ber_decoder in under 30 seconds from a cold start. Similar
experiments on the other new fuzz targets (patches 8-9) also
successfully identified injected bugs, proving that KFuzzTest is
effective when paired with a coverage-guided fuzzing engine.

This patch series is structured as follows:
- Patch 1 introduces the core KFuzzTest API, including the main
  FUZZ_TEST_SIMPLE macro.
- Patch 2 adds the runtime implementation for the framework
- Patch 3 adds documentation.
- Patch 4 provides sample fuzz targets.
- Patch 5 defines fuzz targets for several functions in crypto/.
- Patch 6 adds maintainer information for KFuzzTest.

Changes since PR v3:
- Major simplification of the architecture, removing the complex
  `FUZZ_TEST` macro, the custom serialization format, domain
  constraints, annotations, and associated DWARF metadata regions.
- The framework now only supports `FUZZ_TEST_SIMPLE` targets, which
  accept raw binary data.
- Removed the userspace bridge tool as it is no longer required for
  serializing inputs.
- Updated documentation and samples to reflect the "simple-only"
  approach.

Ethan Graham (6):
  kfuzztest: add user-facing API and data structures
  kfuzztest: implement core module and input processing
  kfuzztest: add ReST documentation
  kfuzztest: add KFuzzTest sample fuzz targets
  crypto: implement KFuzzTest targets for PKCS7 and RSA parsing
  MAINTAINERS: add maintainer information for KFuzzTest

 Documentation/dev-tools/index.rst             |   1 +
 Documentation/dev-tools/kfuzztest.rst         | 152 ++++++++++++++++++
 MAINTAINERS                                   |   7 +
 crypto/asymmetric_keys/Makefile               |   2 +
 crypto/asymmetric_keys/tests/Makefile         |   4 +
 crypto/asymmetric_keys/tests/pkcs7_kfuzz.c    |  18 +++
 .../asymmetric_keys/tests/rsa_helper_kfuzz.c  |  24 +++
 include/asm-generic/vmlinux.lds.h             |  14 +-
 include/linux/kfuzztest.h                     |  90 +++++++++++
 lib/Kconfig.debug                             |   1 +
 lib/Makefile                                  |   2 +
 lib/kfuzztest/Kconfig                         |  16 ++
 lib/kfuzztest/Makefile                        |   4 +
 lib/kfuzztest/input.c                         |  47 ++++++
 lib/kfuzztest/main.c                          | 142 ++++++++++++++++
 samples/Kconfig                               |   7 +
 samples/Makefile                              |   1 +
 samples/kfuzztest/Makefile                    |   3 +
 samples/kfuzztest/underflow_on_buffer.c       |  52 ++++++
 19 files changed, 586 insertions(+), 1 deletion(-)
 create mode 100644 Documentation/dev-tools/kfuzztest.rst
 create mode 100644 crypto/asymmetric_keys/tests/Makefile
 create mode 100644 crypto/asymmetric_keys/tests/pkcs7_kfuzz.c
 create mode 100644 crypto/asymmetric_keys/tests/rsa_helper_kfuzz.c
 create mode 100644 include/linux/kfuzztest.h
 create mode 100644 lib/kfuzztest/Kconfig
 create mode 100644 lib/kfuzztest/Makefile
 create mode 100644 lib/kfuzztest/input.c
 create mode 100644 lib/kfuzztest/main.c
 create mode 100644 samples/kfuzztest/Makefile
 create mode 100644 samples/kfuzztest/underflow_on_buffer.c

-- 
2.51.0