AFLplusplus/gcc_plugin/afl-gcc-rt.o.c

/*
   american fuzzy lop - GCC plugin instrumentation bootstrap
   ---------------------------------------------------------

   Written by Austin Seipp <aseipp@pobox.com> and
              Laszlo Szekeres <lszekeres@google.com> and
              Michal Zalewski

   GCC integration design is based on the LLVM design, which comes
   from Laszlo Szekeres.

   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

   This code is the rewrite of afl-as.h's main_payload.

*/

#ifdef __ANDROID__
#include "android-ashmem.h"
#endif
#include "../config.h"
#include "../types.h"

#include <stdlib.h>
#include <signal.h>
#include <unistd.h>
#include <string.h>
#include <assert.h>

#include <sys/mman.h>
#include <sys/shm.h>
#include <sys/wait.h>
#include <sys/types.h>

#include <sys/mman.h>
#include <fcntl.h>

/* Globals needed by the injected instrumentation. The __afl_area_initial region
   is used for instrumentation output before __afl_map_shm() has a chance to
   run. It will end up as .comm, so it shouldn't be too wasteful. */

u8  __afl_area_initial[MAP_SIZE];
u8 *__afl_area_ptr = __afl_area_initial;

#ifdef __ANDROID__
u32 __afl_prev_loc;
#else
__thread u32 __afl_prev_loc;
#endif

/* Trace a basic block with some ID */
void __afl_trace(const u32 x) {

#if 1                                      /* enable for neverZero feature. */
  __afl_area_ptr[__afl_prev_loc ^ x] +=
      1 + ((u8)(1 + __afl_area_ptr[__afl_prev_loc ^ x]) == 0);
#else
  ++__afl_area_ptr[__afl_prev_loc ^ x];
#endif

  __afl_prev_loc = (x >> 1);
  return;

}

/* Running in persistent mode? */

static u8 is_persistent;

/* SHM setup. */

static void __afl_map_shm(void) {

  u8 *id_str = getenv(SHM_ENV_VAR);

  /* If we're running under AFL, attach to the appropriate region, replacing the
     early-stage __afl_area_initial region that is needed to allow some really
     hacky .init code to work correctly in projects such as OpenSSL. */

  if (id_str) {

#ifdef USEMMAP
    const char *   shm_file_path = id_str;
    int            shm_fd = -1;
    unsigned char *shm_base = NULL;

    /* create the shared memory segment as if it was a file */
    shm_fd = shm_open(shm_file_path, O_RDWR, 0600);
    if (shm_fd == -1) {

      printf("shm_open() failed\n");
      exit(1);

    }

    /* map the shared memory segment to the address space of the process */
    shm_base = mmap(0, MAP_SIZE, PROT_READ | PROT_WRITE, MAP_SHARED, shm_fd, 0);
    if (shm_base == MAP_FAILED) {

      close(shm_fd);
      shm_fd = -1;

      printf("mmap() failed\n");
      exit(2);

    }

    __afl_area_ptr = shm_base;
#else
    u32 shm_id = atoi(id_str);

    __afl_area_ptr = shmat(shm_id, NULL, 0);
#endif

    /* Whooooops. */

    if (__afl_area_ptr == (void *)-1) exit(1);

    /* Write something into the bitmap so that even with low AFL_INST_RATIO,
       our parent doesn't give up on us. */

    __afl_area_ptr[0] = 1;

  }

}

/* Fork server logic. */

static void __afl_start_forkserver(void) {

  static u8 tmp[4];
  s32       child_pid;

  u8 child_stopped = 0;

  void (*old_sigchld_handler)(int) = signal(SIGCHLD, SIG_DFL);

  /* Phone home and tell the parent that we're OK. If parent isn't there,
     assume we're not running in forkserver mode and just execute program. */

  if (write(FORKSRV_FD + 1, tmp, 4) != 4) return;

  while (1) {

    u32 was_killed;
    int status;

    /* Wait for parent by reading from the pipe. Abort if read fails. */

    if (read(FORKSRV_FD, &was_killed, 4) != 4) exit(1);

    /* If we stopped the child in persistent mode, but there was a race
       condition and afl-fuzz already issued SIGKILL, write off the old
       process. */

    if (child_stopped && was_killed) {

      child_stopped = 0;
      if (waitpid(child_pid, &status, 0) < 0) exit(1);

    }

    if (!child_stopped) {

      /* Once woken up, create a clone of our process. */

      child_pid = fork();
      if (child_pid < 0) exit(1);

      /* In child process: close fds, resume execution. */

      if (!child_pid) {

        signal(SIGCHLD, old_sigchld_handler);

        close(FORKSRV_FD);
        close(FORKSRV_FD + 1);
        return;

      }

    } else {

      /* Special handling for persistent mode: if the child is alive but
         currently stopped, simply restart it with SIGCONT. */

      kill(child_pid, SIGCONT);
      child_stopped = 0;

    }

    /* In parent process: write PID to pipe, then wait for child. */

    if (write(FORKSRV_FD + 1, &child_pid, 4) != 4) exit(1);

    if (waitpid(child_pid, &status, is_persistent ? WUNTRACED : 0) < 0) exit(1);

    /* In persistent mode, the child stops itself with SIGSTOP to indicate
       a successful run. In this case, we want to wake it up without forking
       again. */

    if (WIFSTOPPED(status)) child_stopped = 1;

    /* Relay wait status to pipe, then loop back. */

    if (write(FORKSRV_FD + 1, &status, 4) != 4) exit(1);

  }

}

/* A simplified persistent mode handler, used as explained in README.llvm. */

int __afl_persistent_loop(unsigned int max_cnt) {

  static u8  first_pass = 1;
  static u32 cycle_cnt;

  if (first_pass) {

    /* Make sure that every iteration of __AFL_LOOP() starts with a clean slate.
       On subsequent calls, the parent will take care of that, but on the first
       iteration, it's our job to erase any trace of whatever happened
       before the loop. */

    if (is_persistent) {

      memset(__afl_area_ptr, 0, MAP_SIZE);
      __afl_area_ptr[0] = 1;
      __afl_prev_loc = 0;

    }

    cycle_cnt = max_cnt;
    first_pass = 0;
    return 1;

  }

  if (is_persistent) {

    if (--cycle_cnt) {

      raise(SIGSTOP);

      __afl_area_ptr[0] = 1;
      __afl_prev_loc = 0;

      return 1;

    } else {

      /* When exiting __AFL_LOOP(), make sure that the subsequent code that
         follows the loop is not traced. We do that by pivoting back to the
         dummy output region. */

      __afl_area_ptr = __afl_area_initial;

    }

  }

  return 0;

}

/* This one can be called from user code when deferred forkserver mode
    is enabled. */

void __afl_manual_init(void) {

  static u8 init_done;

  if (!init_done) {

    __afl_map_shm();
    __afl_start_forkserver();
    init_done = 1;

  }

}

/* Proper initialization routine. */

__attribute__((constructor(101))) void __afl_auto_init(void) {

  is_persistent = !!getenv(PERSIST_ENV_VAR);

  if (getenv(DEFER_ENV_VAR)) return;

  __afl_manual_init();

}