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/**************************************************************************/
/* */
/* OCaml */
/* */
/* Stephen Dolan, University of Cambridge */
/* */
/* Copyright 2016 Stephen Dolan. */
/* */
/* All rights reserved. This file is distributed under the terms of */
/* the GNU Lesser General Public License version 2.1, with the */
/* special exception on linking described in the file LICENSE. */
/* */
/**************************************************************************/
/* Runtime support for afl-fuzz */
#define CAML_INTERNALS
#include <string.h>
#include "caml/config.h"
#include "caml/memory.h"
#include "caml/mlvalues.h"
/* Values used by the instrumentation logic (see cmmgen.ml) */
#define INITIAL_AFL_AREA_SIZE (1 << 16)
unsigned char * caml_afl_area_ptr = NULL;
uintnat caml_afl_prev_loc;
#if !defined(HAS_SYS_SHM_H) || !defined(HAS_SHMAT)
CAMLexport value caml_setup_afl(value unit)
{
/* AFL is not supported, but we still need to allocate space for the bitmap
(the instrumented OCaml code will write into it). */
if (caml_afl_area_ptr == NULL) {
caml_afl_area_ptr = caml_stat_alloc(INITIAL_AFL_AREA_SIZE);
memset(caml_afl_area_ptr, 0, INITIAL_AFL_AREA_SIZE);
}
return Val_unit;
}
CAMLprim value caml_reset_afl_instrumentation(value full)
{
return Val_unit;
}
#else
#include <unistd.h>
#include <sys/types.h>
#include <signal.h>
#include <sys/shm.h>
#include <sys/wait.h>
#include <stdio.h>
#include <string.h>
#include "caml/domain.h"
#include "caml/misc.h"
#include "caml/osdeps.h"
static int afl_initialised = 0;
/* afl uses abnormal termination (SIGABRT) to check whether
to count a testcase as "crashing" */
extern int caml_abort_on_uncaught_exn;
/* File descriptors used to synchronise with afl-fuzz */
#define FORKSRV_FD_READ 198
#define FORKSRV_FD_WRITE 199
static void afl_write(uint32_t msg)
{
if (write(FORKSRV_FD_WRITE, &msg, 4) != 4)
caml_fatal_error("writing to afl-fuzz");
}
static uint32_t afl_read(void)
{
uint32_t msg;
if (read(FORKSRV_FD_READ, &msg, 4) != 4)
caml_fatal_error("reading from afl-fuzz");
return msg;
}
CAMLexport value caml_setup_afl(value unit)
{
char* shm_id_str;
char* shm_id_end;
long int shm_id;
uint32_t startup_msg = 0;
if (afl_initialised) return Val_unit;
afl_initialised = 1;
shm_id_str = caml_secure_getenv("__AFL_SHM_ID");
if (shm_id_str == NULL) {
/* Not running under afl-fuzz. Allocate space for the bitmap
(the instrumented OCaml code will write into it),
and continue as normal. */
caml_afl_area_ptr = caml_stat_alloc(INITIAL_AFL_AREA_SIZE);
memset(caml_afl_area_ptr, 0, INITIAL_AFL_AREA_SIZE);
return Val_unit;
}
/* if afl-fuzz is attached, we want it to know about uncaught exceptions */
caml_abort_on_uncaught_exn = 1;
shm_id = strtol(shm_id_str, &shm_id_end, 10);
if (!(*shm_id_str != '\0' && *shm_id_end == '\0'))
caml_fatal_error("afl-fuzz: bad shm id");
caml_afl_area_ptr = shmat((int)shm_id, NULL, 0);
if (caml_afl_area_ptr == (void*)-1)
caml_fatal_error("afl-fuzz: could not attach shm area");
/* poke the bitmap so that afl-fuzz knows we exist, even if the
application has sparse instrumentation */
caml_afl_area_ptr[0] = 1;
/* synchronise with afl-fuzz */
if (write(FORKSRV_FD_WRITE, &startup_msg, 4) != 4) {
/* initial write failed, so assume we're not meant to fork.
afl-tmin uses this mode. */
return Val_unit;
}
afl_read();
/* ensure that another module has not already spawned a domain */
if (caml_domain_is_multicore())
caml_fatal_error("afl-fuzz: cannot fork with multiple domains running");
while (1) {
int child_pid = fork();
if (child_pid < 0) caml_fatal_error("afl-fuzz: could not fork");
else if (child_pid == 0) {
caml_atfork_hook();
/* Run the program */
close(FORKSRV_FD_READ);
close(FORKSRV_FD_WRITE);
return Val_unit;
}
/* As long as the child keeps raising SIGSTOP, we reuse the same process */
while (1) {
int status;
uint32_t was_killed;
afl_write((uint32_t)child_pid);
/* WUNTRACED means wait until termination or SIGSTOP */
if (waitpid(child_pid, &status, WUNTRACED) < 0)
caml_fatal_error("afl-fuzz: waitpid failed");
afl_write((uint32_t)status);
was_killed = afl_read();
if (WIFSTOPPED(status)) {
/* child stopped, waiting for another test case */
if (was_killed) {
/* we saw the child stop, but since then afl-fuzz killed it.
we should wait for it before forking another child */
if (waitpid(child_pid, &status, 0) < 0)
caml_fatal_error("afl-fuzz: waitpid failed");
break;
} else {
kill(child_pid, SIGCONT);
}
} else {
/* child died */
break;
}
}
}
}
CAMLprim value caml_reset_afl_instrumentation(value full)
{
if (full == Val_true && caml_afl_area_ptr != NULL) {
memset(caml_afl_area_ptr, 0, INITIAL_AFL_AREA_SIZE);
}
caml_afl_prev_loc = 0;
return Val_unit;
}
#endif /* HAS_SYS_SHM_H */
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