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83f88df757
GCC and Clang allow us to inject a call to a function named __sanitizer_cov_trace_pc on every edge. This function has to be defined by us. By noting down the caller in that function we can trace the code we have encountered during execution. Such information is used by coverage guided fuzzers like AFL and LibFuzzer to determine if a new input resulted in a new code path. This makes fuzzing much more effective. Additionally this adds a basic KCOV implementation. KCOV is an API that allows user space to request the kernel to start collecting coverage information for a given user space thread. Furthermore KCOV then exposes the collected program counters to user space via a BlockDevice which can be mmaped from user space. This work is required to add effective support for fuzzing SerenityOS to the Syzkaller syscall fuzzer. :^) :^)
60 lines
1.4 KiB
C++
60 lines
1.4 KiB
C++
/*
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* Copyright (c) 2021, Patrick Meyer <git@the-space.agency>
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*
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* SPDX-License-Identifier: BSD-2-Clause
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*/
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#include <fcntl.h>
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#include <stdio.h>
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#include <sys/ioctl.h>
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#include <sys/ioctl_numbers.h>
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#include <sys/kcov.h>
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#include <sys/mman.h>
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#include <unistd.h>
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// Note: This program requires serenity to be built with the CMake build option
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// ENABLE_KERNEL_COVERAGE_COLLECTION
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int main(void)
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{
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constexpr size_t num_entries = 1024 * 100;
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int fd = open("/dev/kcov", O_RDWR);
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if (fd == -1) {
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perror("open");
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return 1;
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}
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if (ioctl(fd, KCOV_SETBUFSIZE, num_entries) == -1) {
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perror("ioctl: KCOV_SETBUFSIZE");
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return 1;
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}
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kcov_pc_t* cover = (kcov_pc_t*)mmap(NULL, num_entries * KCOV_ENTRY_SIZE,
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PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0);
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if (cover == MAP_FAILED) {
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perror("mmap");
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return 1;
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}
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if (ioctl(fd, KCOV_ENABLE) == -1) {
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perror("ioctl: KCOV_ENABLE");
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return 1;
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}
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cover[0] = 0;
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// Example syscall so we actually cover some kernel code.
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getppid();
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if (ioctl(fd, KCOV_DISABLE) == -1) {
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perror("ioctl: KCOV_DISABLE");
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return 1;
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}
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u64 cov_idx = cover[0];
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for (size_t idx = 1; idx <= cov_idx; idx++)
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printf("%p\n", (void*)cover[idx]);
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if (munmap(const_cast<u64*>(cover), num_entries * KCOV_ENTRY_SIZE) == -1) {
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perror("munmap");
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return 1;
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}
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close(fd);
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return 0;
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}
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