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//===- FuzzerUtilFuchsia.cpp - Misc utils for Fuchsia. --------------------===//
// The LLVM Compiler Infrastructure
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
// Misc utils implementation using Fuchsia/Zircon APIs.
#include "FuzzerDefs.h"
#include "FuzzerInternal.h"
#include "FuzzerUtil.h"
#include <cerrno>
#include <cinttypes>
#include <cstdint>
#include <fcntl.h>
#include <lib/fdio/spawn.h>
#include <string>
#include <sys/select.h>
#include <thread>
#include <unistd.h>
#include <zircon/errors.h>
#include <zircon/process.h>
#include <zircon/sanitizer.h>
#include <zircon/status.h>
#include <zircon/syscalls.h>
#include <zircon/syscalls/debug.h>
#include <zircon/syscalls/exception.h>
#include <zircon/syscalls/port.h>
#include <zircon/types.h>
namespace fuzzer {
// Given that Fuchsia doesn't have the POSIX signals that libFuzzer was written
// around, the general approach is to spin up dedicated threads to watch for
// each requested condition (alarm, interrupt, crash). Of these, the crash
// handler is the most involved, as it requires resuming the crashed thread in
// order to invoke the sanitizers to get the needed state.
// Forward declaration of assembly trampoline needed to resume crashed threads.
// This appears to have external linkage to C++, which is why it's not in the
// anonymous namespace. The assembly definition inside MakeTrampoline()
// actually defines the symbol with internal linkage only.
void CrashTrampolineAsm() __asm__("CrashTrampolineAsm");
namespace {
// TODO(phosek): remove this and replace it with ZX_TIME_INFINITE
// A magic value for the Zircon exception port, chosen to spell 'FUZZING'
// when interpreted as a byte sequence on little-endian platforms.
const uint64_t kFuzzingCrash = 0x474e495a5a5546;
// Helper function to handle Zircon syscall failures.
void ExitOnErr(zx_status_t Status, const char *Syscall) {
if (Status != ZX_OK) {
Printf("libFuzzer: %s failed: %s\n", Syscall,
void AlarmHandler(int Seconds) {
while (true) {
void InterruptHandler() {
fd_set readfds;
// Ctrl-C sends ETX in Zircon.
do {
select(STDIN_FILENO + 1, &readfds, nullptr, nullptr, nullptr);
} while(!FD_ISSET(STDIN_FILENO, &readfds) || getchar() != 0x03);
// For the crash handler, we need to call Fuzzer::StaticCrashSignalCallback
// without POSIX signal handlers. To achieve this, we use an assembly function
// to add the necessary CFI unwinding information and a C function to bridge
// from that back into C++.
// FIXME: This works as a short-term solution, but this code really shouldn't be
// architecture dependent. A better long term solution is to implement remote
// unwinding and expose the necessary APIs through sanitizer_common and/or ASAN
// to allow the exception handling thread to gather the crash state directly.
// Alternatively, Fuchsia may in future actually implement basic signal
// handling for the machine trap signals.
#if defined(__x86_64__)
OP_REG(rax) \
OP_REG(rbx) \
OP_REG(rcx) \
OP_REG(rdx) \
OP_REG(rsi) \
OP_REG(rdi) \
OP_REG(rbp) \
OP_REG(rsp) \
OP_REG(r8) \
OP_REG(r9) \
OP_REG(r10) \
OP_REG(r11) \
OP_REG(r12) \
OP_REG(r13) \
OP_REG(r14) \
OP_REG(r15) \
#elif defined(__aarch64__)
OP_NUM(0) \
OP_NUM(1) \
OP_NUM(2) \
OP_NUM(3) \
OP_NUM(4) \
OP_NUM(5) \
OP_NUM(6) \
OP_NUM(7) \
OP_NUM(8) \
OP_NUM(9) \
OP_NUM(10) \
OP_NUM(11) \
OP_NUM(12) \
OP_NUM(13) \
OP_NUM(14) \
OP_NUM(15) \
OP_NUM(16) \
OP_NUM(17) \
OP_NUM(18) \
OP_NUM(19) \
OP_NUM(20) \
OP_NUM(21) \
OP_NUM(22) \
OP_NUM(23) \
OP_NUM(24) \
OP_NUM(25) \
OP_NUM(26) \
OP_NUM(27) \
OP_NUM(28) \
OP_NUM(29) \
OP_NUM(30) \
#error "Unsupported architecture for fuzzing on Fuchsia"
// Produces a CFI directive for the named or numbered register.
#define CFI_OFFSET_REG(reg) ".cfi_offset " #reg ", %c[" #reg "]\n"
#define CFI_OFFSET_NUM(num) CFI_OFFSET_REG(r##num)
// Produces an assembler input operand for the named or numbered register.
#define ASM_OPERAND_REG(reg) \
[reg] "i"(offsetof(zx_thread_state_general_regs_t, reg)),
#define ASM_OPERAND_NUM(num) \
[r##num] "i"(offsetof(zx_thread_state_general_regs_t, r[num])),
// Trampoline to bridge from the assembly below to the static C++ crash
// callback.
static void StaticCrashHandler() {
for (;;) {
// Creates the trampoline with the necessary CFI information to unwind through
// to the crashing call stack. The attribute is necessary because the function
// is never called; it's just a container around the assembly to allow it to
// use operands for compile-time computed constants.
void MakeTrampoline() {
".pushsection .text.CrashTrampolineAsm\n"
".type CrashTrampolineAsm,STT_FUNC\n"
".cfi_startproc simple\n"
#if defined(__x86_64__)
".cfi_return_column rip\n"
".cfi_def_cfa rsp, 0\n"
"call %c[StaticCrashHandler]\n"
#elif defined(__aarch64__)
".cfi_return_column 33\n"
".cfi_def_cfa sp, 0\n"
".cfi_offset 33, %c[pc]\n"
"bl %[StaticCrashHandler]\n"
#error "Unsupported architecture for fuzzing on Fuchsia"
".size CrashTrampolineAsm, . - CrashTrampolineAsm\n"
: // No outputs
#if defined(__aarch64__)
[StaticCrashHandler] "i" (StaticCrashHandler));
void CrashHandler(zx_handle_t *Event) {
// This structure is used to ensure we close handles to objects we create in
// this handler.
struct ScopedHandle {
~ScopedHandle() { _zx_handle_close(Handle); }
zx_handle_t Handle = ZX_HANDLE_INVALID;
// Create and bind the exception port. We need to claim to be a "debugger" so
// the kernel will allow us to modify and resume dying threads (see below).
// Once the port is set, we can signal the main thread to continue and wait
// for the exception to arrive.
ScopedHandle Port;
ExitOnErr(_zx_port_create(0, &Port.Handle), "_zx_port_create");
zx_handle_t Self = _zx_process_self();
ExitOnErr(_zx_task_bind_exception_port(Self, Port.Handle, kFuzzingCrash,
ExitOnErr(_zx_object_signal(*Event, 0, ZX_USER_SIGNAL_0),
zx_port_packet_t Packet;
ExitOnErr(_zx_port_wait(Port.Handle, ZX_TIME_INFINITE_OLD, &Packet),
// At this point, we want to get the state of the crashing thread, but
// libFuzzer and the sanitizers assume this will happen from that same thread
// via a POSIX signal handler. "Resurrecting" the thread in the middle of the
// appropriate callback is as simple as forcibly setting the instruction
// pointer/program counter, provided we NEVER EVER return from that function
// (since otherwise our stack will not be valid).
ScopedHandle Thread;
ExitOnErr(_zx_object_get_child(Self, Packet.exception.tid,
ZX_RIGHT_SAME_RIGHTS, &Thread.Handle),
zx_thread_state_general_regs_t GeneralRegisters;
ExitOnErr(_zx_thread_read_state(Thread.Handle, ZX_THREAD_STATE_GENERAL_REGS,
&GeneralRegisters, sizeof(GeneralRegisters)),
// To unwind properly, we need to push the crashing thread's register state
// onto the stack and jump into a trampoline with CFI instructions on how
// to restore it.
#if defined(__x86_64__)
uintptr_t StackPtr =
(GeneralRegisters.rsp - (128 + sizeof(GeneralRegisters))) &
__unsanitized_memcpy(reinterpret_cast<void *>(StackPtr), &GeneralRegisters,
GeneralRegisters.rsp = StackPtr; = reinterpret_cast<zx_vaddr_t>(CrashTrampolineAsm);
#elif defined(__aarch64__)
uintptr_t StackPtr =
(GeneralRegisters.sp - sizeof(GeneralRegisters)) & -(uintptr_t)16;
__unsanitized_memcpy(reinterpret_cast<void *>(StackPtr), &GeneralRegisters,
GeneralRegisters.sp = StackPtr;
GeneralRegisters.pc = reinterpret_cast<zx_vaddr_t>(CrashTrampolineAsm);
#error "Unsupported architecture for fuzzing on Fuchsia"
// Now force the crashing thread's state.
ExitOnErr(_zx_thread_write_state(Thread.Handle, ZX_THREAD_STATE_GENERAL_REGS,
&GeneralRegisters, sizeof(GeneralRegisters)),
ExitOnErr(_zx_task_resume_from_exception(Thread.Handle, Port.Handle, 0),
} // namespace
// Platform specific functions.
void SetSignalHandler(const FuzzingOptions &Options) {
// Set up alarm handler if needed.
if (Options.UnitTimeoutSec > 0) {
std::thread T(AlarmHandler, Options.UnitTimeoutSec / 2 + 1);
// Set up interrupt handler if needed.
if (Options.HandleInt || Options.HandleTerm) {
std::thread T(InterruptHandler);
// Early exit if no crash handler needed.
if (!Options.HandleSegv && !Options.HandleBus && !Options.HandleIll &&
!Options.HandleFpe && !Options.HandleAbrt)
// Set up the crash handler and wait until it is ready before proceeding.
zx_handle_t Event;
ExitOnErr(_zx_event_create(0, &Event), "_zx_event_create");
std::thread T(CrashHandler, &Event);
zx_status_t Status = _zx_object_wait_one(Event, ZX_USER_SIGNAL_0,
ExitOnErr(Status, "_zx_object_wait_one");
void SleepSeconds(int Seconds) {
unsigned long GetPid() {
zx_status_t rc;
zx_info_handle_basic_t Info;
if ((rc = _zx_object_get_info(_zx_process_self(), ZX_INFO_HANDLE_BASIC, &Info,
sizeof(Info), NULL, NULL)) != ZX_OK) {
Printf("libFuzzer: unable to get info about self: %s\n",
return Info.koid;
size_t GetPeakRSSMb() {
zx_status_t rc;
zx_info_task_stats_t Info;
if ((rc = _zx_object_get_info(_zx_process_self(), ZX_INFO_TASK_STATS, &Info,
sizeof(Info), NULL, NULL)) != ZX_OK) {
Printf("libFuzzer: unable to get info about self: %s\n",
return (Info.mem_private_bytes + Info.mem_shared_bytes) >> 20;
template <typename Fn>
class RunOnDestruction {
explicit RunOnDestruction(Fn fn) : fn_(fn) {}
~RunOnDestruction() { fn_(); }
Fn fn_;
template <typename Fn>
RunOnDestruction<Fn> at_scope_exit(Fn fn) {
return RunOnDestruction<Fn>(fn);
int ExecuteCommand(const Command &Cmd) {
zx_status_t rc;
// Convert arguments to C array
auto Args = Cmd.getArguments();
size_t Argc = Args.size();
assert(Argc != 0);
std::unique_ptr<const char *[]> Argv(new const char *[Argc + 1]);
for (size_t i = 0; i < Argc; ++i)
Argv[i] = Args[i].c_str();
Argv[Argc] = nullptr;
// Determine stdout
if (Cmd.hasOutputFile()) {
auto Filename = Cmd.getOutputFile();
FdOut = open(Filename.c_str(), O_WRONLY | O_CREAT | O_TRUNC, 0);
if (FdOut == -1) {
Printf("libFuzzer: failed to open %s: %s\n", Filename.c_str(),
return ZX_ERR_IO;
auto CloseFdOut = at_scope_exit([&]() { close(FdOut); } );
// Determine stderr
if (Cmd.isOutAndErrCombined())
FdErr = FdOut;
// Clone the file descriptors into the new process
fdio_spawn_action_t SpawnAction[] = {
.fd =
.local_fd = STDIN_FILENO,
.target_fd = STDIN_FILENO,
.fd =
.local_fd = FdOut,
.target_fd = STDOUT_FILENO,
.fd =
.local_fd = FdErr,
.target_fd = STDERR_FILENO,
// Start the process.
zx_handle_t ProcessHandle = ZX_HANDLE_INVALID;
rc = fdio_spawn_etc(
Argv[0], Argv.get(), nullptr, 3, SpawnAction, &ProcessHandle, ErrorMsg);
if (rc != ZX_OK) {
Printf("libFuzzer: failed to launch '%s': %s, %s\n", Argv[0], ErrorMsg,
return rc;
auto CloseHandle = at_scope_exit([&]() { _zx_handle_close(ProcessHandle); });
// Now join the process and return the exit status.
if ((rc = _zx_object_wait_one(ProcessHandle, ZX_PROCESS_TERMINATED,
ZX_TIME_INFINITE_OLD, nullptr)) != ZX_OK) {
Printf("libFuzzer: failed to join '%s': %s\n", Argv[0],
return rc;
zx_info_process_t Info;
if ((rc = _zx_object_get_info(ProcessHandle, ZX_INFO_PROCESS, &Info,
sizeof(Info), nullptr, nullptr)) != ZX_OK) {
Printf("libFuzzer: unable to get return code from '%s': %s\n", Argv[0],
return rc;
return Info.return_code;
const void *SearchMemory(const void *Data, size_t DataLen, const void *Patt,
size_t PattLen) {
return memmem(Data, DataLen, Patt, PattLen);
} // namespace fuzzer