mac/arch.c

/*
 *
 * honggfuzz - architecture dependent code (MAC OS X)
 * -----------------------------------------
 *
 * Author: Robert Swiecki <swiecki@google.com> Felix Gröbert
 * <groebert@google.com>
 *
 * Copyright 2010-2015 by Google Inc. All Rights Reserved.
 *
 * Licensed under the Apache License, Version 2.0 (the "License"); you may
 * not use this file except in compliance with the License. You may obtain
 * a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or
 * implied. See the License for the specific language governing
 * permissions and limitations under the License.
 *
 */

#include "common.h"
#include "arch.h"

#include <ctype.h>
#include <dirent.h>
#include <errno.h>
#include <fcntl.h>
#include <signal.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/cdefs.h>
#include <sys/mman.h>
#include <sys/time.h>
#include <sys/types.h>
#include <sys/wait.h>
#include <sys/resource.h>
#include <time.h>
#include <unistd.h>

#include "log.h"
#include "util.h"
#include "files.h"

#include <servers/bootstrap.h>
#include <mach/mach.h>
#include <mach/mach_vm.h>
#include <mach/mach_types.h>
#include <mach/i386/thread_status.h>
#include <mach/task_info.h>
#include <pthread.h>

#include "mach_exc.h"
#include "mach_excServer.h"

#import <Foundation/Foundation.h>

/*
 * Interface to third_party/CrashReport_*.o
 */
/*  *INDENT-OFF* */
@interface CrashReport : NSObject - (id) initWithTask:(task_t)
    task exceptionType:(exception_type_t)
    anExceptionType exceptionCode:(mach_exception_data_t)
    anExceptionCode exceptionCodeCount:(mach_msg_type_number_t)
    anExceptionCodeCount thread:(thread_t)
    thread threadStateFlavor:(thread_state_flavor_t)
    aThreadStateFlavor threadState:(thread_state_data_t)
    aThreadState threadStateCount:(mach_msg_type_number_t) aThreadStateCount;
@end
/*  *INDENT-ON* */

/*
 * Global to have exception port available in the collection thread
 */
static mach_port_t g_exception_port = MACH_PORT_NULL;

/*
 * From xnu/bsd/sys/proc_internal.h
 */
#define PID_MAX 99999

/*
 * Global to store crash info in exception handler thread
 */
fuzzer_t g_fuzzer_crash_information[PID_MAX + 1];

/*
 * Global to have a unique service name for each honggfuzz process
 */
char g_service_name[256];

struct {
    bool important;
    const char *descr;
} arch_sigs[NSIG];

__attribute__ ((constructor))
void arch_initSigs(void)
{
    for (int x = 0; x < NSIG; x++)
        arch_sigs[x].important = false;

    arch_sigs[SIGILL].important = true;
    arch_sigs[SIGILL].descr = "SIGILL";
    arch_sigs[SIGFPE].important = true;
    arch_sigs[SIGFPE].descr = "SIGFPE";
    arch_sigs[SIGSEGV].important = true;
    arch_sigs[SIGSEGV].descr = "SIGSEGV";
    arch_sigs[SIGBUS].important = true;
    arch_sigs[SIGBUS].descr = "SIGBUS";
    arch_sigs[SIGABRT].important = true;
    arch_sigs[SIGABRT].descr = "SIGABRT";
}

const char *exception_to_string(int exception)
{
    switch (exception) {
    case EXC_BAD_ACCESS:
        return "EXC_BAD_ACCESS";
    case EXC_BAD_INSTRUCTION:
        return "EXC_BAD_INSTRUCTION";
    case EXC_ARITHMETIC:
        return "EXC_ARITHMETIC";
    case EXC_EMULATION:
        return "EXC_EMULATION";
    case EXC_SOFTWARE:
        return "EXC_SOFTWARE";
    case EXC_BREAKPOINT:
        return "EXC_BREAKPOINT";
    case EXC_SYSCALL:
        return "EXC_SYSCALL";
    case EXC_MACH_SYSCALL:
        return "EXC_MACH_SYSCALL";
    case EXC_RPC_ALERT:
        return "EXC_RPC_ALERT";
    case EXC_CRASH:
        return "EXC_CRASH";
    }
    return "UNKNOWN";
}

/*
 * Returns true if a process exited (so, presumably, we can delete an input
 * file)
 */
static bool arch_analyzeSignal(honggfuzz_t * hfuzz, int status, fuzzer_t * fuzzer)
{
    /*
     * Resumed by delivery of SIGCONT
     */
    if (WIFCONTINUED(status)) {
        return false;
    }

    /*
     * Boring, the process just exited
     */
    if (WIFEXITED(status)) {
        LOGMSG(l_DEBUG, "Process (pid %d) exited normally with status %d", fuzzer->pid,
               WEXITSTATUS(status));
        return true;
    }

    /*
     * Shouldn't really happen, but, well..
     */
    if (!WIFSIGNALED(status)) {
        LOGMSG(l_ERROR,
               "Process (pid %d) exited with the following status %d, please report that as a bug",
               fuzzer->pid, status);
        return true;
    }

    int termsig = WTERMSIG(status);
    LOGMSG(l_DEBUG, "Process (pid %d) killed by signal %d '%s'", fuzzer->pid, termsig,
           strsignal(termsig));
    if (!arch_sigs[termsig].important) {
        LOGMSG(l_DEBUG, "It's not that important signal, skipping");
        return true;
    }

    /*
     * Signal is interesting
     */
    char newname[PATH_MAX];

    /*
     * Get data from exception handler
     */
    fuzzer->pc = g_fuzzer_crash_information[fuzzer->pid].pc;
    fuzzer->exception = g_fuzzer_crash_information[fuzzer->pid].exception;
    fuzzer->access = g_fuzzer_crash_information[fuzzer->pid].access;
    fuzzer->backtrace = g_fuzzer_crash_information[fuzzer->pid].backtrace;

    if (hfuzz->saveUnique) {
        snprintf(newname, sizeof(newname),
                 "%s.%s.PC.%.16llx.STACK.%.16llx.ADDR.%.16llx.%s.%s",
                 arch_sigs[termsig].descr,
                 exception_to_string(fuzzer->exception), fuzzer->pc,
                 fuzzer->backtrace, fuzzer->access, fuzzer->origFileName, hfuzz->fileExtn);
    } else {

        char localtmstr[PATH_MAX];
        util_getLocalTime("%F.%H.%M.%S", localtmstr, sizeof(localtmstr));

        snprintf(newname, sizeof(newname),
                 "%s.%s.PC.%.16llx.STACK.%.16llx.ADDR.%.16llx.TIME.%s.PID.%.5d.%s.%s",
                 arch_sigs[termsig].descr,
                 exception_to_string(fuzzer->exception), fuzzer->pc,
                 fuzzer->backtrace, fuzzer->access, localtmstr, fuzzer->pid, fuzzer->origFileName,
                 hfuzz->fileExtn);
    }

    if (link(fuzzer->fileName, newname) == 0) {
        LOGMSG(l_INFO, "Ok, that's interesting, saved '%s' as '%s'", fuzzer->fileName, newname);
    } else {
        if (errno == EEXIST) {
            LOGMSG(l_INFO, "It seems that '%s' already exists, skipping", newname);
        } else {
            LOGMSG_P(l_ERROR, "Couldn't link '%s' to '%s'", fuzzer->fileName, newname);
        }
    }

    return true;
}

bool arch_launchChild(honggfuzz_t * hfuzz, char *fileName)
{
#define ARGS_MAX 512
    char *args[ARGS_MAX + 2];
    char argData[PATH_MAX] = { 0 };
    int x;

    for (x = 0; x < ARGS_MAX && hfuzz->cmdline[x]; x++) {
        if (!hfuzz->fuzzStdin && strcmp(hfuzz->cmdline[x], _HF_FILE_PLACEHOLDER) == 0) {
            args[x] = fileName;
        } else if (!hfuzz->fuzzStdin && strstr(hfuzz->cmdline[x], _HF_FILE_PLACEHOLDER)) {
            const char *off = strstr(hfuzz->cmdline[x], _HF_FILE_PLACEHOLDER);
            snprintf(argData, PATH_MAX, "%.*s%s", (int)(off - hfuzz->cmdline[x]), hfuzz->cmdline[x], fileName);
            args[x] = argData;
        } else {
            args[x] = hfuzz->cmdline[x];
        }
    }

    args[x++] = NULL;

    LOGMSG(l_DEBUG, "Launching '%s' on file '%s'", args[0], fileName);

    /*
     * Get child's bootstrap port.
     */
    mach_port_t child_bootstrap = MACH_PORT_NULL;
    if (task_get_bootstrap_port(mach_task_self(), &child_bootstrap) != KERN_SUCCESS) {
        return false;
    }

    /*
     * Get exception port.
     */
    mach_port_t exception_port = MACH_PORT_NULL;

    if (bootstrap_look_up(child_bootstrap, g_service_name, &exception_port)
        != KERN_SUCCESS) {
        return false;
    }

    /*
     * Here we register the exception port in the child
     */
    if (task_set_exception_ports(mach_task_self(),
                                 EXC_MASK_CRASH,
                                 exception_port,
                                 EXCEPTION_STATE_IDENTITY |
                                 MACH_EXCEPTION_CODES, MACHINE_THREAD_STATE) != KERN_SUCCESS) {
        return false;
    }

    /*
     * Set timeout (prof), real timeout (2*prof), and rlimit_cpu (2*prof)
     */
    if (hfuzz->tmOut) {
        struct itimerval it;

        /*
         * The hfuzz->tmOut is real CPU usage time...
         */
        it.it_value.tv_sec = hfuzz->tmOut;
        it.it_value.tv_usec = 0;
        it.it_interval.tv_sec = 0;
        it.it_interval.tv_usec = 0;
        if (setitimer(ITIMER_PROF, &it, NULL) == -1) {
            LOGMSG_P(l_ERROR, "Couldn't set the ITIMER_PROF timer");
            return false;
        }

        /*
         * ...so, if a process sleeps, this one should
         * trigger a signal...
         */
        it.it_value.tv_sec = hfuzz->tmOut;
        it.it_value.tv_usec = 0;
        it.it_interval.tv_sec = 0;
        it.it_interval.tv_usec = 0;
        if (setitimer(ITIMER_REAL, &it, NULL) == -1) {
            LOGMSG_P(l_ERROR, "Couldn't set the ITIMER_REAL timer");
            return false;
        }

        /*
         * ..if a process sleeps and catches SIGPROF/SIGALRM
         * rlimits won't help either. However, arch_checkTimeLimit
         * will send a SIGKILL at tmOut + 2 seconds. That should
         * do it :)
         */
        struct rlimit rl;

        rl.rlim_cur = hfuzz->tmOut + 1;
        rl.rlim_max = hfuzz->tmOut + 1;
        if (setrlimit(RLIMIT_CPU, &rl) == -1) {
            LOGMSG_P(l_ERROR, "Couldn't enforce the RLIMIT_CPU resource limit");
            return false;
        }
    }

    /*
     * The address space limit. If big enough - roughly the size of RAM used
     */
    if (hfuzz->asLimit) {
        struct rlimit rl;

        rl.rlim_cur = hfuzz->asLimit * 1024UL * 1024UL;
        rl.rlim_max = hfuzz->asLimit * 1024UL * 1024UL;
        if (setrlimit(RLIMIT_AS, &rl) == -1) {
            LOGMSG_P(l_DEBUG, "Couldn't encforce the RLIMIT_AS resource limit, ignoring");
        }
    }

    if (hfuzz->nullifyStdio) {
        util_nullifyStdio();
    }

    if (hfuzz->fuzzStdin) {
        /*
         * Uglyyyyyy ;)
         */
        if (!util_redirectStdin(fileName)) {
            return false;
        }
    }

    for (size_t i = 0; i < ARRAYSIZE(hfuzz->envs) && hfuzz->envs[i]; i++) {
        putenv(hfuzz->envs[i]);
    }

    execvp(args[0], args);

    util_recoverStdio();
    LOGMSG(l_FATAL, "Failed to create new '%s' process", args[0]);
    return false;
}

static void arch_checkTimeLimit(honggfuzz_t * hfuzz, fuzzer_t * fuzzer)
{
    if (!hfuzz->tmOut) {
        return;
    }
    int64_t curMillis = util_timeNowMillis();
    int64_t diffMillis = curMillis - fuzzer->timeStartedMillis;
    if (diffMillis > ((hfuzz->tmOut + 2) * 1000)) {
        LOGMSG(l_WARN, "PID %d took too much time (limit %ld s). Sending SIGKILL",
               fuzzer->pid, hfuzz->tmOut);
        kill(fuzzer->pid, SIGKILL);
    }
}

void arch_reapChild(honggfuzz_t * hfuzz, fuzzer_t * fuzzer)
{
    /*
     * First check manually if we have expired childs
     */
    arch_checkTimeLimit(hfuzz, fuzzer);

    /*
     * Now check for signals using wait4
     */
    int options = WUNTRACED;
    if (hfuzz->tmOut) {
        options |= WNOHANG;
    }

    for (;;) {
        int status = 0;
        while (wait4(fuzzer->pid, &status, options, NULL) != fuzzer->pid) {
            if (hfuzz->tmOut) {
                arch_checkTimeLimit(hfuzz, fuzzer);
                usleep(0.20 * 1000000);
            }
        }
        LOGMSG(l_DEBUG, "Process (pid %d) came back with status %d", fuzzer->pid, status);

        if (arch_analyzeSignal(hfuzz, status, fuzzer)) {
            return;
        }
    }
}

void *wait_for_exception()
{
    while (1) {
        mach_msg_server_once(mach_exc_server, 4096, g_exception_port, MACH_MSG_OPTION_NONE);
    }
}

/*
 * Called once before fuzzing starts. Prepare mach ports for attaching crash reporter.
 */
bool arch_archInit(honggfuzz_t * hfuzz)
{
    char plist[PATH_MAX];
    snprintf(plist, sizeof(plist), "/Users/%s/Library/Preferences/com.apple.DebugSymbols.plist",
             getlogin());

    if (files_exists(plist)) {
        LOGMSG(l_WARN,
               "honggfuzz won't work if DBGShellCommands are set in ~/Library/Preferences/com.apple.DebugSymbols.plist");
    }

    /*
     * Allocate exception port.
     */
    if (mach_port_allocate(mach_task_self(), MACH_PORT_RIGHT_RECEIVE, &g_exception_port) !=
        KERN_SUCCESS) {
        return false;
    }

    /*
     * Insert exception receive port.
     */
    if (mach_port_insert_right
        (mach_task_self(), g_exception_port, g_exception_port,
         MACH_MSG_TYPE_MAKE_SEND) != KERN_SUCCESS) {
        return false;
    }

    /*
     * Get bootstrap port.
     */
    mach_port_t bootstrap = MACH_PORT_NULL;
    if (task_get_bootstrap_port(mach_task_self(), &bootstrap) != KERN_SUCCESS) {
        return false;
    }

    /*
     * Generate and register exception port service.
     */
    snprintf(g_service_name, sizeof(g_service_name), "com.google.code.honggfuzz.%d",
             (int)util_rndGet(0, 999999));
    if (bootstrap_check_in(bootstrap, g_service_name, &g_exception_port) != KERN_SUCCESS) {
        return false;
    }

    /*
     * Create a collection thread to catch the exceptions from the
     * children
     */
    pthread_t exception_thread;

    if (pthread_create(&exception_thread, NULL, wait_for_exception, 0)) {
        LOGMSG(l_FATAL, "Parent: could not create thread to wait for child's exception");
        return false;
    }

    if (pthread_detach(exception_thread)) {
        LOGMSG(l_FATAL, "Parent: could not detach thread to wait for child's exception");
        return false;
    }

    return true;
}

/*
 * Write the crash report to DEBUG
 */
void
write_crash_report(thread_port_t thread,
                   task_port_t task,
                   exception_type_t exception,
                   mach_exception_data_t code,
                   mach_msg_type_number_t code_count,
                   int *flavor, thread_state_t in_state, mach_msg_type_number_t in_state_count)
{

    NSAutoreleasePool *pool =[[NSAutoreleasePool alloc] init];
    CrashReport *_crashReport = nil;

    /*  *INDENT-OFF* */
    _crashReport = [[CrashReport alloc] initWithTask:task
                    exceptionType:exception
                    exceptionCode:code
                    exceptionCodeCount:code_count
                    thread:thread
                    threadStateFlavor:*flavor
                    threadState:(thread_state_t)in_state
                    threadStateCount:in_state_count];
    /*  *INDENT-OFF* */

    NSString *crashDescription =[_crashReport description];
    char *description = (char *)[crashDescription UTF8String];

    LOGMSG(l_DEBUG, "CrashReport: %s", description);

    [_crashReport release];
    [pool drain];
}

/* Hash the callstack in an unique way */
uint64_t hash_callstack(thread_port_t thread,
                        task_port_t task,
                        exception_type_t exception,
                        mach_exception_data_t code,
                        mach_msg_type_number_t code_count,
                        int *flavor,
                        thread_state_t in_state,
                        mach_msg_type_number_t in_state_count) {

    NSAutoreleasePool *pool =[[NSAutoreleasePool alloc] init];
    CrashReport *_crashReport = nil;

    /*  *INDENT-OFF* */
    _crashReport = [[CrashReport alloc] initWithTask:task
                    exceptionType:exception
                    exceptionCode:code
                    exceptionCodeCount:code_count
                    thread:thread
                    threadStateFlavor:*flavor
                    threadState:(thread_state_t)in_state
                    threadStateCount:in_state_count];
    /*  *INDENT-ON* */

    NSString *crashDescription =[_crashReport description];
    char *description = (char *)[crashDescription UTF8String];

    /*
     * The callstack begins with the following word
     */
    char *callstack = strstr(description, "Crashed:");

    if (callstack == NULL) {
        LOGMSG(l_FATAL, "Could not find callstack in crash report %s", description);
    }

    /*
     * Scroll forward to the next newline
     */
    char *callstack_start = strstr(callstack, "\n");

    if (callstack_start == NULL) {
        LOGMSG(l_FATAL, "Could not find callstack start in crash report %s", description);
    }

    /*
     * Skip the newline
     */
    callstack_start++;

    /*
     * Determine the end of the callstack
     */
    char *callstack_end = strstr(callstack, "\n\nThread");

    if (callstack_end == NULL) {
        LOGMSG(l_FATAL, "Could not find callstack end in crash report %s", description);
    }

    /*
     * Make sure it's NULL-terminated
     */
    *callstack_end = '\0';

    /*
     *
     * For each line, we only take the last three nibbles from the
     * address.
     *
     * Sample output:
     *
     * 0 libsystem_kernel.dylib 0x00007fff80514d46 __kill + 10 1
     * libsystem_c.dylib 0x00007fff85731ec0 __abort + 193 2
     * libsystem_c.dylib 0x00007fff85732d17 __stack_chk_fail + 195 3
     * stack_buffer_overflow64-stripped 0x000000010339def5 0x10339d000 +
     * 3829 4 ??? 0x4141414141414141 0 + 4702111234474983745
     *
     * 0 libsystem_kernel.dylib 0x00007fff80514d46 __kill + 10 1
     * libsystem_c.dylib 0x00007fff85731ec0 __abort + 193 2
     * libsystem_c.dylib 0x00007fff85732d17 __stack_chk_fail + 195 3
     * stack_buffer_overflow64 0x0000000108f41ef5 main + 133 4 ???
     * 0x4141414141414141 0 + 4702111234474983745
     *
     * 0 libsystem_kernel.dylib 0x940023ba __kill + 10 1
     * libsystem_kernel.dylib 0x940014bc kill$UNIX2003 + 32 2
     * libsystem_c.dylib 0x926f362e __abort + 246 3 libsystem_c.dylib
     * 0x926c2b60 __chk_fail + 49 4 libsystem_c.dylib 0x926c2bf9
     * __memset_chk + 53 5 stack_buffer_overflow32-stripped 0x00093ee5
     * 0x93000 + 3813 6 libdyld.dylib 0x978c6725 start + 1
     *
     * 0 libsystem_kernel.dylib 0x940023ba __kill + 10 1
     * libsystem_kernel.dylib 0x940014bc kill$UNIX2003 + 32 2
     * libsystem_c.dylib 0x926f362e __abort + 246 3 libsystem_c.dylib
     * 0x926c2b60 __chk_fail + 49 4 libsystem_c.dylib 0x926c2bf9
     * __memset_chk + 53 5 stack_buffer_overflow32 0x0003cee5 main + 117 6
     * libdyld.dylib 0x978c6725 start + 1
     *
     */

    uint64_t hash = 0;
    char *pos = callstack_start;

    /*
     * Go through each line until we run out of lines
     */
    while (strstr(pos, "\t") != NULL) {
        /*
         * Format: dylib spaces tab address space symbol space plus space offset
         * Scroll pos forward to the last three nibbles of the address.
         */
        if ((pos = strstr(pos, "\t")) == NULL)
            break;
        if ((pos = strstr(pos, " ")) == NULL)
            break;
        pos = pos - 3;
        /*
         * Hash the last three nibbles
         */
        hash ^= util_hash(pos, 3);
        /*
         * Scroll pos one forward to skip the current tab
         */
        pos++;
    }

    LOGMSG(l_DEBUG, "Callstack hash %u", hash);

    [_crashReport release];
    [pool drain];

    return hash;
}

kern_return_t
catch_mach_exception_raise(mach_port_t exception_port,
                           mach_port_t thread,
                           mach_port_t task,
                           exception_type_t exception, mach_exception_data_t code,
                           mach_msg_type_number_t codeCnt)
{
    LOGMSG(l_FATAL, "This function should never get called");
    return KERN_SUCCESS;
}

kern_return_t
catch_mach_exception_raise_state(mach_port_t exception_port,
                                 exception_type_t exception,
                                 const mach_exception_data_t code,
                                 mach_msg_type_number_t codeCnt,
                                 int *flavor,
                                 const thread_state_t old_state,
                                 mach_msg_type_number_t old_stateCnt,
                                 thread_state_t new_state, mach_msg_type_number_t * new_stateCnt)
{
    LOGMSG(l_FATAL, "This function should never get called");
    return KERN_SUCCESS;
}

kern_return_t catch_mach_exception_raise_state_identity( __attribute__ ((unused))
                                                        exception_port_t exception_port,
                                                        thread_port_t thread,
                                                        task_port_t task,
                                                        exception_type_t exception,
                                                        mach_exception_data_t code,
                                                        mach_msg_type_number_t
                                                        code_count, int *flavor,
                                                        thread_state_t in_state,
                                                        mach_msg_type_number_t
                                                        in_state_count,
                                                        thread_state_t out_state,
                                                        mach_msg_type_number_t * out_state_count)
{
    if (exception != EXC_CRASH) {
        LOGMSG(l_FATAL, "Got non EXC_CRASH! This should not happen.");
    }

    /*
     * We will save our results to the honggfuzz_t global
     */
    pid_t pid;
    pid_for_task(task, &pid);
    LOGMSG(l_DEBUG, "Crash of pid %d", pid);

    fuzzer_t *fuzzer = &g_fuzzer_crash_information[pid];

    /*
     * Get program counter.
     * Cast to void* in order to silence the alignment warnings
     */

    x86_thread_state_t *platform_in_state = ((x86_thread_state_t *) (void *)in_state);

    if (x86_THREAD_STATE32 == platform_in_state->tsh.flavor) {
        fuzzer->pc = platform_in_state->uts.ts32.__eip;
    } else {
        fuzzer->pc = platform_in_state->uts.ts64.__rip;
    }

    /*
     * Get the exception type
     */

    exception_type_t exception_type = ((code[0] >> 20) & 0x0F);

    if (exception_type == 0) {
        exception_type = EXC_CRASH;
    }

    fuzzer->exception = exception_type;

    /*
     * Get the access address.
     */

    mach_exception_data_type_t exception_data[2];
    memcpy(exception_data, code, sizeof(exception_data));
    exception_data[0] = (code[0] & ~(0x00000000FFF00000));
    exception_data[1] = code[1];

    mach_exception_data_type_t access_address = exception_data[1];
    fuzzer->access = (uint64_t) access_address;

    /*
     * Get a hash of the callstack
     */

    uint64_t hash = hash_callstack(thread, task, exception, code, code_count, flavor,
                                   in_state, in_state_count);

    fuzzer->backtrace = hash;

    /*
     * Cleanup
     */

    if (mach_port_deallocate(mach_task_self(), task) != KERN_SUCCESS) {
        LOGMSG(l_WARN, "Exception Handler: Could not deallocate task");
    }

    if (mach_port_deallocate(mach_task_self(), thread) != KERN_SUCCESS) {
        LOGMSG(l_WARN, "Exception Handler: Could not deallocate thread");
    }

    return KERN_SUCCESS;        // KERN_SUCCESS indicates that this should
    // not be forwarded to other crash
    // handlers
}