模糊测试（即简单地提供可能无效、意外或随机的数据作为程序的输入）是在大型软件系统中查找错误的一种极其有效的方法，也是软件开发生命周期中的重要组成部分。
Android 的构建系统通过包含 LLVM 编译器基础架构项目的 libFuzzer 来支持模糊测试。LibFuzzer 与被测库链接，并处理模糊测试会话期间发生的所有输入选择、突变和崩溃报告。LLVM 的 Sanitizers 用于帮助进行内存损坏检测和代码覆盖率指标。
本文介绍了 Android 上的 libFuzzer 以及如何执行插桩构建。它还包括编写、运行和自定义模糊器的说明。
设置和构建
为了确保您在设备上运行的是可正常工作的映像，您可以下载工厂映像并刷写到设备。或者，您可以下载 AOSP 源代码并按照下面的设置和构建示例操作。
设置示例
此示例假定目标设备是 Pixel (taimen) 并且已为 USB 调试做好准备 (aosp_taimen-userdebug)。您可以从驱动程序二进制文件下载其他 Pixel 二进制文件。
mkdir ~/binexport PATH=~/bin:$PATHcurl https://storage.googleapis.com/git-repo-downloads/repo > ~/bin/repochmod a+x ~/bin/reporepo init -u https://android.googlesource.com/platform/manifest -b mainrepo sync -c -j8wget https://dl.google.com/dl/android/aosp/google_devices-taimen-qq1a.191205.008-f4537f93.tgztar xvf google_devices-taimen-qq1a.191205.008-f4537f93.tgz./extract-google_devices-taimen.shwget https://dl.google.com/dl/android/aosp/qcom-taimen-qq1a.191205.008-760afa6e.tgztar xvf qcom-taimen-qq1a.191205.008-760afa6e.tgz./extract-qcom-taimen.sh. build/envsetup.shlunch aosp_taimen-userdebug
构建示例
运行模糊测试目标的第一步是获取全新的系统映像。我们建议至少使用最新开发版本的 Android。
- 通过发出以下命令执行初始构建
m
- 为了允许您刷写设备，请使用适当的按键组合将设备启动到 fastboot 模式。
- 解锁 Bootloader 并使用以下命令刷写新编译的映像。
fastboot oem unlockfastboot flashall
目标设备现在应该已准备好进行 libFuzzer 模糊测试。
编写模糊器
为了演示如何使用 Android 中的 libFuzzer 编写端到端模糊器，请使用以下易受攻击的代码作为测试用例。这有助于测试模糊器，确保一切正常运行，并说明崩溃数据的外观。
这是测试函数。
#include <stdint.h> #include <stddef.h> bool FuzzMe(const char *data, size_t dataSize) { return dataSize >= 3 && data[0] == 'F' && data[1] == 'U' && data[2] == 'Z' && data[3] == 'Z'; // ← Out of bounds access }
构建并运行此测试模糊器
- 模糊测试目标由两个文件组成：一个构建文件和一个模糊测试目标源代码。在要进行模糊测试的库旁边的位置创建文件。为模糊器指定一个描述模糊器用途的名称。
- 使用 libFuzzer 编写模糊测试目标。模糊测试目标是一个函数，它接受指定大小的数据 blob，并将其传递给要进行模糊测试的函数。以下是易受攻击的测试函数的基本模糊器
#include <stddef.h> #include <stdint.h> extern "C" int LLVMFuzzerTestOneInput(const char *data, size_t size) { // ... // Use the data to call the library you are fuzzing. // ... return FuzzMe(data, size); }
- 告知 Android 的构建系统创建模糊器二进制文件。要构建模糊器，请将此代码添加到
Android.bp文件中cc_fuzz { name: "fuzz_me_fuzzer", srcs: [ "fuzz_me_fuzzer.cpp", ], // If the fuzzer has a dependent library, uncomment the following section and // include it. // static_libs: [ // "libfoo", // Dependent library // ], // // The advanced features below allow you to package your corpus and // dictionary files during building. You can find more information about // these features at: // - Corpus: https://llvm.net.cn/docs/LibFuzzer.html#corpus // - Dictionaries: https://llvm.net.cn/docs/LibFuzzer.html#dictionaries // These features are not required for fuzzing, but are highly recommended // to gain extra coverage. // To include a corpus folder, uncomment the following line. // corpus: ["corpus/*"], // To include a dictionary, uncomment the following line. // dictionary: "fuzz_me_fuzzer.dict", }
- 要为在目标设备（设备）上运行制作模糊器
SANITIZE_TARGET=hwaddress m fuzz_me_fuzzer
- 要为在主机上运行制作模糊器
SANITIZE_HOST=address m fuzz_me_fuzzer
为了方便起见，请定义一些 shell 变量，其中包含模糊测试目标的路径和二进制文件的名称（来自您之前编写的构建文件）。
export FUZZER_NAME=your_fuzz_target
完成这些步骤后，您应该已构建模糊器。模糊器的默认位置（对于此示例 Pixel 构建）为
在主机上运行模糊器
host_supported: true,
$ANDROID_HOST_OUT/fuzz/x86_64/$FUZZER_NAME/$FUZZER_NAME
在设备上运行模糊器
我们希望使用 adb 将其复制到您的设备。
- 要将这些文件上传到设备上的目录，请运行以下命令
adb rootadb sync data - 使用此命令在设备上运行测试模糊器
adb shell /data/fuzz/$(get_build_var TARGET_ARCH)/$FUZZER_NAME/$FUZZER_NAME \ /data/fuzz/$(get_build_var TARGET_ARCH)/$FUZZER_NAME/corpus
这将产生类似于以下示例输出的输出。
INFO: Seed: 913963180
INFO: Loaded 2 modules (16039 inline 8-bit counters): 16033 [0x7041769b88, 0x704176da29), 6 [0x60e00f4df0, 0x60e00f4df6),
INFO: Loaded 2 PC tables (16039 PCs): 16033 [0x704176da30,0x70417ac440), 6 [0x60e00f4df8,0x60e00f4e58),
INFO: -max_len is not provided; libFuzzer will not generate inputs larger than 4096 bytes
INFO: A corpus is not provided, starting from an empty corpus
#2 INITED cov: 5 ft: 5 corp: 1/1b exec/s: 0 rss: 24Mb
#10 NEW cov: 6 ft: 6 corp: 2/4b lim: 4 exec/s: 0 rss: 24Mb L: 3/3 MS: 3 CopyPart-ChangeByte-InsertByte-
#712 NEW cov: 7 ft: 7 corp: 3/9b lim: 8 exec/s: 0 rss: 24Mb L: 5/5 MS: 2 InsertByte-InsertByte-
#744 REDUCE cov: 7 ft: 7 corp: 3/7b lim: 8 exec/s: 0 rss: 25Mb L: 3/3 MS: 2 ShuffleBytes-EraseBytes-
#990 REDUCE cov: 8 ft: 8 corp: 4/10b lim: 8 exec/s: 0 rss: 25Mb L: 3/3 MS: 1 ChangeByte-
==18631==ERROR: HWAddressSanitizer: tag-mismatch on address 0x0041e00b4183 at pc 0x0060e00c5144
READ of size 1 at 0x0041e00b4183 tags: f8/03 (ptr/mem) in thread T0
#0 0x60e00c5140 (/data/fuzz/arm64/example_fuzzer/example_fuzzer+0xf140)
#1 0x60e00ca130 (/data/fuzz/arm64/example_fuzzer/example_fuzzer+0x14130)
#2 0x60e00c9b8c (/data/fuzz/arm64/example_fuzzer/example_fuzzer+0x13b8c)
#3 0x60e00cb188 (/data/fuzz/arm64/example_fuzzer/example_fuzzer+0x15188)
#4 0x60e00cbdec (/data/fuzz/arm64/example_fuzzer/example_fuzzer+0x15dec)
#5 0x60e00d8fbc (/data/fuzz/arm64/example_fuzzer/example_fuzzer+0x22fbc)
#6 0x60e00f0a98 (/data/fuzz/arm64/example_fuzzer/example_fuzzer+0x3aa98)
#7 0x7041b75d34 (/data/fuzz/arm64/lib/libc.so+0xa9d34)
[0x0041e00b4180,0x0041e00b41a0) is a small allocated heap chunk; size: 32 offset: 3
0x0041e00b4183 is located 0 bytes to the right of 3-byte region [0x0041e00b4180,0x0041e00b4183)
allocated here:
#0 0x70418392bc (/data/fuzz/arm64/lib/libclang_rt.hwasan-aarch64-android.so+0x212bc)
#1 0x60e00ca040 (/data/fuzz/arm64/example_fuzzer/example_fuzzer+0x14040)
#2 0x60e00c9b8c (/data/fuzz/arm64/example_fuzzer/example_fuzzer+0x13b8c)
#3 0x60e00cb188 (/data/fuzz/arm64/example_fuzzer/example_fuzzer+0x15188)
#4 0x60e00cbdec (/data/fuzz/arm64/example_fuzzer/example_fuzzer+0x15dec)
#5 0x60e00d8fbc (/data/fuzz/arm64/example_fuzzer/example_fuzzer+0x22fbc)
#6 0x60e00f0a98 (/data/fuzz/arm64/example_fuzzer/example_fuzzer+0x3aa98)
#7 0x7041b75d34 (/data/fuzz/arm64/lib/libc.so+0xa9d34)
#8 0x60e00c504c (/data/fuzz/arm64/example_fuzzer/example_fuzzer+0xf04c)
#9 0x70431aa9c4 (/data/fuzz/arm64/example_fuzzer/example_fuzzer+0x519c4)
Thread: T1 0x006700006000 stack: [0x007040c55000,0x007040d4ecc0) sz: 1023168 tls: [0x000000000000,0x000000000000)
Thread: T0 0x006700002000 stack: [0x007fe51f3000,0x007fe59f3000) sz: 8388608 tls: [0x000000000000,0x000000000000)
Memory tags around the buggy address (one tag corresponds to 16 bytes):
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
08 00 cf 08 dc 08 cd 08 b9 08 1a 1a 0b 00 04 3f
=> 27 00 08 00 bd bd 2d 07 [03] 73 66 66 27 27 20 f6 <=
5b 5b 87 87 03 00 01 00 4f 04 24 24 03 39 2c 2c
05 00 04 00 be be 85 85 04 00 4a 4a 05 05 5f 5f
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
Tags for short granules around the buggy address (one tag corresponds to 16 bytes):
04 .. .. cf .. dc .. cd .. b9 .. .. 3f .. 57 ..
=> .. .. 21 .. .. .. .. 2d [f8] .. .. .. .. .. .. .. <=
.. .. .. .. 9c .. e2 .. .. 4f .. .. 99 .. .. ..
See https://clang.llvm.net.cn/docs/HardwareAssistedAddressSanitizerDesign.html#short-granules for a description of short granule tags
Registers where the failure occurred (pc 0x0060e00c5144):
x0 f8000041e00b4183 x1 000000000000005a x2 0000000000000006 x3 000000704176d9c0
x4 00000060e00f4df6 x5 0000000000000004 x6 0000000000000046 x7 000000000000005a
x8 00000060e00f4df0 x9 0000006800000000 x10 0000000000000001 x11 00000060e0126a00
x12 0000000000000001 x13 0000000000000231 x14 0000000000000000 x15 000e81434c909ede
x16 0000007041838b14 x17 0000000000000003 x18 0000007042b80000 x19 f8000041e00b4180
x20 0000006800000000 x21 000000000000005a x22 24000056e00b4000 x23 00000060e00f5200
x24 00000060e0128c88 x25 00000060e0128c20 x26 00000060e0128000 x27 00000060e0128000
x28 0000007fe59f16e0 x29 0000007fe59f1400 x30 00000060e00c5144
SUMMARY: HWAddressSanitizer: tag-mismatch (/data/fuzz/arm64/example_fuzzer/example_fuzzer+0xf140)
MS: 1 ChangeByte-; base unit: e09f9c158989c56012ccd88111b82f778a816eae
0x46,0x55,0x5a,
FUZ
artifact_prefix='./'; Test unit written to ./crash-0eb8e4ed029b774d80f2b66408203801cb982a60
Base64: RlVa
在示例输出中，崩溃是由 fuzz_me_fuzzer.cpp 的第 10 行引起的
data[3] == 'Z'; // :(
如果 data 的长度为 3，则这是一个简单的越界读取。
在运行模糊器之后，输出通常会导致崩溃，并且有问题的输入将保存在语料库中并获得一个 ID。在示例输出中，这是 crash-0eb8e4ed029b774d80f2b66408203801cb982a60。
要在设备上进行模糊测试时检索崩溃信息，请发出此命令，并指定您的崩溃 ID
adb pull /data/fuzz/arm64/fuzz_me_fuzzer/corpus/CRASH_ID
在主机上进行模糊测试时，崩溃信息会出现在运行模糊器的本地文件夹中的崩溃文件夹中。
生成行覆盖率
行覆盖率对于开发人员非常有用，因为他们可以查明代码中未覆盖的区域，并相应地更新其模糊器，以便在未来的模糊测试运行中覆盖这些区域。
- 为了生成模糊器覆盖率报告，请运行以下步骤
CLANG_COVERAGE=true NATIVE_COVERAGE_PATHS='*' make ${FUZZER_NAME} - 将模糊器及其依赖项推送到设备后，使用
LLVM_PROFILE_FILE运行模糊测试目标，如下所示DEVICE_TRACE_PATH=/data/fuzz/$(get_build_var TARGET_ARCH)/${FUZZER_NAME}/data.profrawadb shell LLVM_PROFILE_FILE=${DEVICE_TRACE_PATH} /data/fuzz/$(get_build_var TARGET_ARCH)/${FUZZER_NAME}/${FUZZER_NAME} -runs=1000 - 通过首先从设备中拉取 profraw 文件，然后将 html 报告生成到名为 coverage-html 的文件夹中来生成覆盖率报告，如下所示
adb pull ${DEVICE_TRACE_PATH} data.profrawllvm-profdata merge --sparse data.profraw --output data.profdatallvm-cov show --format=html --instr-profile=data.profdata \ symbols/data/fuzz/$(get_build_var TARGET_ARCH)/${FUZZER_NAME}/${FUZZER_NAME} \ --output-dir=coverage-html --path-equivalence=/proc/self/cwd/,$ANDROID_BUILD_TOP