Fuzzers for libkeymaster4

Plugin Design Considerations

The fuzzer plugins for libkeymaster4 are designed based on the understanding of the source code and try to achieve the following:

Maximize code coverage

The configuration parameters are not hardcoded, but instead selected based on incoming data. This ensures more code paths are reached by the fuzzers.

libkeymaster4 supports the following parameters:

1. Security Level (parameter name: securityLevel)
2. Padding Mode (parameter name: paddingMode)
3. Digest (parameter name: digest)
4. Key Format (parameter name: keyFormat)
5. Key Purpose (parameter name: keyPurpose)

Parameter	Valid Values	Configured Value
securityLevel	0.SecurityLevel::SOFTWARE 1.SecurityLevel::TRUSTED_ENVIRONMENT 2.SecurityLevel::STRONGBOX	Value obtained from FuzzedDataProvider
paddingMode	0.PaddingMode::NONE 1.PaddingMode::RSA_OAEP 2.PaddingMode::RSA_PSS 3. PaddingMode::RSA_PKCS1_1_5_ENCRYPT 4.PaddingMode::RSA_PKCS1_1_5_SIGN 5.PaddingMode::PKCS7	Value obtained from FuzzedDataProvider
digest	1. Digest::NONE 2.Digest::MD5 3.Digest::SHA1 4.Digest::SHA_2_224 5.Digest::SHA_2_256 6.Digest::SHA_2_384 7.Digest::SHA_2_512	Value obtained from FuzzedDataProvider
keyFormat	1. KeyFormat::X509 2.KeyFormat::PKCS8 3.KeyFormat::RAW	Value obtained from FuzzedDataProvider
keyPurpose	1. KeyPurpose::ENCRYPT 2.KeyPurpose::DECRYPT 3.KeyPurpose::SIGN 4. KeyPurpose::VERIFY 5. KeyPurpose::WRAP_KEY	Value obtained from FuzzedDataProvider

This also ensures that the plugins are always deterministic for any given input.

Maximize utilization of input data

The plugins feed the entire input data to the module. This ensures that the plugins tolerate any kind of input (empty, huge, malformed, etc) and dont exit() on any input and thereby increasing the chance of identifying vulnerabilities.

Build

This describes steps to build k4_AndroidKeymaster4Device_fuzzer and k4_keymaster_configuration_fuzzer binaries

Android

Steps to build

Build the fuzzer

  $ mm k4_AndroidKeymaster4Device_fuzzer
  $ mm k4_keymaster_configuration_fuzzer

Steps to run

To run on device

  $ adb sync data
  $ adb shell /data/fuzz/${TARGET_ARCH}/k4_AndroidKeymaster4Device_fuzzer/k4_AndroidKeymaster4Device_fuzzer
  $ adb shell /data/fuzz/${TARGET_ARCH}/k4_keymaster_configuration_fuzzer/k4_keymaster_configuration_fuzzer

References:

• http://llvm.org/docs/LibFuzzer.html
• https://github.com/google/oss-fuzz