/**
* The entry point for passing a signal to a user signal handler
*
* See manpage for SA_SIGINFO function.
*/
void app_signal_handler(int signal, siginfo_t *siginfo, void *v_context) {
int signal_index = signal_map[(signal % MAX_SIGNAL_NUM)];
if ( (void *)app_actions[signal_index].sa_sigaction == (void *)SIG_IGN ) {
udi_printf("Signal %d ignored, not passing to application\n", signal);
return;
}
if ( (void *)app_actions[signal_index].sa_sigaction == (void *)SIG_DFL ) {
// TODO need to emulate the default action
return;
}
sigset_t cur_set;
if ( setsigmask(SIG_SETMASK, &app_actions[signal_index].sa_mask,
&cur_set) != 0 )
{
udi_printf("failed to adjust blocked signals for application handler: %s\n",
strerror(errno));
}
app_actions[signal_index].sa_sigaction(signal, siginfo, v_context);
if ( setsigmask(SIG_SETMASK, &cur_set, NULL) != 0 ) {
udi_printf("failed to reset blocked signals after application handler: %s\n",
strerror(errno));
}
}
/**
* Install any breakpoints necessary to capture any interesting events
* that cannot be captured by wrapping functions
*
* @param errmsg the errmsg populated on error
*
* @return 0 on success; non-zero on failure
*/
int install_event_breakpoints(udi_errmsg *errmsg) {
int errnum = 0;
do {
// Exit cannot be wrappped because Linux executables can call it
// directly and do not pass through the PLT
exit_bp = create_breakpoint((udi_address)(unsigned long)exit);
if ( exit_bp == NULL ) {
udi_printf("%s\n", "failed to create exit breakpoint");
errnum = -1;
break;
}
errnum = install_breakpoint(exit_bp, errmsg);
if ( errnum != 0 ) {
udi_printf("%s\n", "failed to install exit breakpoint");
errnum = -1;
break;
}
if (get_multithread_capable()) {
errnum = install_thread_event_breakpoints(errmsg);
}
} while(0);
return errnum;
}
/**
* Use dynamic loader to locate functions that are wrapped by library
* wrappers
*
* @param errmsg the errmsg populated on error
*
* @return 0 on success; non-zero on failure
*/
int locate_wrapper_functions(udi_errmsg *errmsg) {
int errnum = 0;
char *errmsg_tmp;
// reset dlerror()
dlerror();
do {
// locate symbols for wrapper functions
real_sigaction = (sigaction_type) dlsym(UDI_RTLD_NEXT, "sigaction");
errmsg_tmp = dlerror();
if (errmsg_tmp != NULL) {
udi_printf("symbol lookup error: %s\n", errmsg_tmp);
strncpy(errmsg->msg, errmsg_tmp, errmsg->size-1);
errnum = -1;
break;
}
real_fork = (fork_type) dlsym(UDI_RTLD_NEXT, "fork");
errmsg_tmp = dlerror();
if (errmsg_tmp != NULL) {
udi_printf("symbol lookup error: %s\n", errmsg_tmp);
strncpy(errmsg->msg, errmsg_tmp, errmsg->size-1);
errnum = -1;
break;
}
real_execve = (execve_type) dlsym(UDI_RTLD_NEXT, "execve");
errmsg_tmp = dlerror();
if (errmsg_tmp != NULL) {
udi_printf("symbol lookup error: %s\n", errmsg_tmp);
strncpy(errmsg->msg, errmsg_tmp, errmsg->size-1);
errnum = -1;
break;
}
real_signal = (signal_type) dlsym(UDI_RTLD_NEXT, "signal");
errmsg_tmp = dlerror();
if (errmsg_tmp != NULL) {
udi_printf("symbol lookup error: %s\n", errmsg_tmp);
strncpy(errmsg->msg, errmsg_tmp, errmsg->size-1);
errnum = -1;
break;
}
} while(0);
return errnum;
}
/**
* Determines the argument to the exit function, given the context at which the exit breakpoint
* was hit
*
* @param context the current context
* @param errmsg the error message populated by the memory access
*
* @return the exit result
*/
exit_result get_exit_argument(const ucontext_t *context, udi_errmsg *errmsg) {
exit_result ret;
ret.failure = 0;
if (__WORDSIZE == 64) {
// The exit argument is passed in rax
ret.status = (int)context->uc_mcontext.gregs[X86_64_RAX_OFFSET];
}else{
// The exit argument is the first parameter on the stack
// Get the stack pointer
unsigned long sp;
sp = (unsigned long)context->uc_mcontext.gregs[X86_ESP_OFFSET];
int word_length = sizeof(unsigned long);
// skip return address
sp += word_length;
int read_result = read_memory(&(ret.status), (const void *)sp, sizeof(int), errmsg);
if ( read_result != 0 ) {
udi_printf("failed to retrieve exit status off of the stack at 0x%lx\n",
sp);
snprintf(errmsg->msg, errmsg->size,
"failed to retrieve exit status off of the stack at 0x%lx: %s",
sp, get_mem_errstr());
ret.failure = read_result;
}
}
return ret;
}
/**
* Waits and executes a command -- used by syscall wrappers
*/
static
void wait_and_execute_command_with_response() {
udi_errmsg errmsg;
errmsg.size = ERRMSG_SIZE;
errmsg.msg[ERRMSG_SIZE-1] = '\0';
thread *request_thr;
int req_result = wait_and_execute_command(&errmsg, &request_thr);
if ( req_result != REQ_SUCCESS ) {
if ( req_result > REQ_SUCCESS ) {
strncpy(errmsg.msg, strerror(req_result), errmsg.size-1);
}
udi_printf("failed to process command: %s\n", errmsg.msg);
udi_response resp = create_response_error(&errmsg);
if ( resp.packed_data != NULL ) {
// explicitly ignore errors
if (request_thr != NULL) {
write_response_to_thr_request(request_thr, &resp);
} else {
write_response(&resp);
}
udi_free(resp.packed_data);
}
}
}
/**
* Sets up the signal handlers for all catchable signals
*
* @return 0 on success; non-zero on failure
*/
int setup_signal_handlers() {
int errnum = 0;
// Define the default sigaction for the library
memset(&default_lib_action, 0, sizeof(struct sigaction));
default_lib_action.sa_sigaction = signal_entry_point;
sigfillset(&(default_lib_action.sa_mask));
default_lib_action.sa_flags = SA_SIGINFO | SA_NODEFER;
// initialize application sigactions and signal map
int i;
for (i = 0; i < NUM_SIGNALS; ++i) {
memset(&app_actions[i], 0, sizeof(struct sigaction));
app_actions[i].sa_handler = SIG_DFL;
signal_map[(signals[i] % MAX_SIGNAL_NUM)] = i;
}
// Sanity check
if ( (sizeof(signals) / sizeof(int)) != NUM_SIGNALS ) {
udi_printf("%s\n", "ASSERT FAIL: signals array length != NUM_SIGNALS");
return -1;
}
for(i = 0; i < NUM_SIGNALS; ++i) {
if ( real_sigaction(signals[i], &default_lib_action, &app_actions[i]) != 0 ) {
errnum = errno;
break;
}
}
return errnum;
}
/**
* The wrapper function for the fork system call.
*
* See fork manpage for description.
*/
pid_t fork() {
pid_t child = real_fork();
if ( child == 0 ) {
reinit_udi_rt();
} else {
uint64_t thread_id = get_user_thread_id();
udi_printf(">>> fork entry for 0x%"PRIx64"/%u\n",
get_user_thread_id(),
get_kernel_thread_id());
// Need to continue waiting until this thread owns the control of the process
int block_result = 1;
while (block_result > 0) {
block_result = block_other_threads();
if ( block_result == -1 ) {
udi_printf("%s\n", "failed to block other threads");
errno = EAGAIN;
return -1;
}
}
// create the event
udi_event_internal event = create_event_fork(thread_id, child);
do {
int errnum = write_event(&event);
if ( errnum != 0 ) {
udi_printf("failed to write fork event: %s\n", strerror(errnum));
errno = EAGAIN;
return -1;
}
} while(0);
wait_and_execute_command_with_response();
int release_result = release_other_threads();
if ( release_result != 0 ) {
udi_printf("%s\n", "failed to release other threads");
errno = EAGAIN;
return -1;
}
}
return child;
}
/**
* Gets mapped memory from the OS
*
* @param length the size of memory area to map (in bytes)
*
* @return the mapped memory
*/
unsigned char *map_mem(size_t length) {
void * ret = mmap(NULL, length, PROT_READ | PROT_WRITE | PROT_EXEC, MAP_ANONYMOUS
| MAP_PRIVATE, -1, 0);
if ( ret == MAP_FAILED ) {
udi_printf("mmap failed: %s\n", strerror(errno));
return NULL;
}
return ret;
}
/**
* Handle the occurence of a hit on the exit breakpoint. This includes gathering all information
* neccessary to create the exit event.
*
* @param context the context for the breakpoint
* @param errmsg the error message populated on error
*
* @return the information extracted about the exit event
*/
static
event_result handle_exit_breakpoint(const ucontext_t *context, udi_errmsg *errmsg) {
event_result result;
result.failure = 0;
result.wait_for_request = 1;
exit_result exit_result = get_exit_argument(context, errmsg);
if ( exit_result.failure ) {
result.failure = exit_result.failure;
return result;
}
udi_printf("exit entered with status %d\n", exit_result.status);
exiting = 1;
// create the event
udi_event_internal exit_event = create_event_exit(get_user_thread_id(), exit_result.status);
do {
if ( exit_event.packed_data == NULL ) {
result.failure = 1;
break;
}
result.failure = write_event(&exit_event);
udi_free(exit_event.packed_data);
} while(0);
if ( result.failure ) {
udi_printf("failed to report exit status of %d\n", exit_result.status);
} else {
if ( udi_debug_on ) {
dump_heap();
}
}
return result;
}