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// KCOV glue for libfuzzer. Build as:
// clang tools/kcovfuzzer/kcovfuzzer.c -fsanitize=fuzzer -static -Wall -o fuzzer
// Run as:
//
// KCOVFUZZER=bpf ./fuzzer -max_len=129 corpus_bpf
// KCOVFUZZER=trace_filter ./fuzzer -max_len=100 -only_ascii=1 corpus_trace_filter
// KCOVFUZZER=binfmt ./fuzzer -max_len=30 -only_ascii=1 corpus_binfmt
//
// If you build with -static, then the following env needs to be exported:
// UBSAN_OPTIONS="handle_segv=0 handle_sigbus=0 handle_abort=0 handle_sigill=0 handle_sigtrap=0 handle_sigfpe=0"
// and the following flags added to fuzzer invocation:
// -timeout=0 -rss_limit_mb=0 -handle_segv=0 -handle_bus=0 -handle_abrt=0 -handle_ill=0 \
// -handle_fpe=0 -handle_int=0 -handle_term=0 -handle_xfsz=0 -handle_usr1=0 -handle_usr2=0
#define _GNU_SOURCE
#include <errno.h>
#include <fcntl.h>
#include <linux/bpf.h>
#include <memory.h>
#include <stdarg.h>
#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>
#include <sys/ioctl.h>
#include <sys/mman.h>
#include <sys/stat.h>
#include <sys/syscall.h>
#include <sys/types.h>
#include <unistd.h>
void init(const char*, long);
void dump_input(const char*, long);
void (*fuzz_func)(const char*, long) = init;
void fail(const char* msg, ...);
void cover_start();
void cover_stop();
int LLVMFuzzerTestOneInput(const char* data, long size)
{
dump_input(data, size);
fuzz_func(data, size);
return 0;
}
void bpf(const char* data, long size)
{
union bpf_attr attr;
memset(&attr, 0, sizeof(attr));
attr.map_type = BPF_MAP_TYPE_HASH;
attr.key_size = 8;
attr.value_size = 8;
attr.max_entries = 2;
int mfd = syscall(SYS_bpf, BPF_MAP_CREATE, &attr, sizeof(attr));
memset(&attr, 0, sizeof(attr));
attr.prog_type = BPF_PROG_TYPE_SOCKET_FILTER;
attr.insns = (uint64_t)data;
attr.insn_cnt = size / 8;
attr.license = (uint64_t)"GPL";
cover_start();
int pfd = syscall(SYS_bpf, BPF_PROG_LOAD, &attr, sizeof(attr));
if (pfd != -1) {
memset(&attr, 0, sizeof(attr));
attr.test.prog_fd = pfd;
syscall(SYS_bpf, BPF_PROG_TEST_RUN, &attr, sizeof(attr));
}
cover_stop();
close(pfd);
close(mfd);
}
void trace_filter(const char* data, long size)
{
int fd0 = open("/sys/kernel/debug/tracing/events/syscalls/sys_exit_read/enable", O_RDWR);
if (fd0 == -1)
fail("open enable failed");
int fd1 = open("/sys/kernel/debug/tracing/events/syscalls/sys_exit_read/filter", O_RDWR);
if (fd1 == -1)
fail("open filter failed");
int fd2 = open("/sys/kernel/debug/tracing/events/syscalls/sys_exit_read/trigger", O_RDWR);
if (fd2 == -1)
fail("open trigger failed");
cover_start();
char buf[256];
buf[0] = '1';
write(fd0, buf, 1);
write(fd1, data, size);
read(fd1, buf, sizeof(buf));
buf[0] = '0';
write(fd1, buf, 1);
write(fd2, data, size);
read(fd2, buf, sizeof(buf));
buf[0] = '0';
write(fd0, buf, 1);
cover_stop();
close(fd0);
close(fd1);
close(fd2);
}
void binfmt(const char* data, long size)
{
static int fd = -1;
if (fd == -1)
fd = open("/proc/sys/fs/binfmt_misc/register", O_WRONLY);
if (fd == -1)
fail("open(/proc/sys/fs/binfmt_misc/register) failed");
cover_start();
write(fd, data, size);
cover_stop();
}
#define KCOV_COVER_SIZE (256 << 10)
#define KCOV_TRACE_PC 0
#define KCOV_INIT_TRACE64 _IOR('c', 1, uint64_t)
#define KCOV_ENABLE _IO('c', 100)
__attribute__((section("__libfuzzer_extra_counters"))) unsigned char libfuzzer_coverage[32 << 10];
uint64_t* kcov_data;
void init(const char* data, long size)
{
const char* name = getenv("KCOVFUZZER");
if (strcmp(name, "bpf") == 0)
fuzz_func = bpf;
else if (strcmp(name, "trace_filter") == 0)
fuzz_func = trace_filter;
else if (strcmp(name, "binfmt") == 0)
fuzz_func = binfmt;
else
fail("unknown fuzz function '%s'", name);
int kcov = open("/sys/kernel/debug/kcov", O_RDWR);
if (kcov == -1)
fail("open of /sys/kernel/debug/kcov failed");
if (ioctl(kcov, KCOV_INIT_TRACE64, KCOV_COVER_SIZE))
fail("cover init trace write failed");
kcov_data = (uint64_t*)mmap(NULL, KCOV_COVER_SIZE * sizeof(kcov_data[0]),
PROT_READ | PROT_WRITE, MAP_SHARED, kcov, 0);
if (kcov_data == MAP_FAILED)
fail("cover mmap failed");
if (ioctl(kcov, KCOV_ENABLE, KCOV_TRACE_PC))
fail("cover enable write trace failed");
close(kcov);
fuzz_func(data, size);
}
void cover_start()
{
__atomic_store_n(&kcov_data[0], 0, __ATOMIC_RELAXED);
}
void cover_stop()
{
uint64_t ncov = __atomic_load_n(&kcov_data[0], __ATOMIC_RELAXED);
if (ncov >= KCOV_COVER_SIZE)
fail("too much cover: %llu", ncov);
for (uint64_t i = 0; i < ncov; i++) {
uint64_t pc = __atomic_load_n(&kcov_data[i + 1], __ATOMIC_RELAXED);
libfuzzer_coverage[pc % sizeof(libfuzzer_coverage)]++;
}
}
void dump_input(const char* data, long size)
{
static int kmsg = -1;
if (kmsg == -1) {
kmsg = open("/dev/kmsg", O_WRONLY);
if (kmsg == -1)
fail("open(/dev/kmsg) failed");
int printk_devkmsg = open("/proc/sys/kernel/printk_devkmsg", O_WRONLY);
if (printk_devkmsg == -1)
fail("open(/proc/sys/kernel/printk_devkmsg) failed");
if (write(printk_devkmsg, "on", 3) != 3)
fail("write(/proc/sys/kernel/printk_devkmsg) failed");
close(printk_devkmsg);
}
char buf[1024];
char* pos = buf + sprintf(buf, "INPUT[%ld]: ", size);
for (long i = 0; i < size; i++) {
if (pos > buf + sizeof(buf) - 10) {
*pos++ = '.';
*pos++ = '.';
*pos++ = '.';
break;
}
char ch = data[i];
if (ch >= 0x20 && ch < 0x7f && ch != '\\') {
*pos++ = ch;
continue;
}
*pos++ = '\\';
*pos++ = 'x';
char hi = ch >> 4;
if (hi <= 9)
*pos++ = '0' + hi;
else
*pos++ = 'a' + hi - 9;
char lo = ch & 0xf;
if (lo <= 9)
*pos++ = '0' + lo;
else
*pos++ = 'a' + lo - 9;
}
*pos++ = '\n';
if (write(kmsg, buf, pos - buf) != pos - buf)
fail("write(/dev/kmsg) failed");
}
void fail(const char* msg, ...)
{
int e = errno;
va_list args;
va_start(args, msg);
vfprintf(stderr, msg, args);
va_end(args);
fprintf(stderr, " (errno %d)\n", e);
_exit(1);
}
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