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afl-llvm-rt.o.c

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+/*
+  Copyright 2015 Google LLC 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.
+*/
+
+/*
+   american fuzzy lop - LLVM instrumentation bootstrap
+   ---------------------------------------------------
+
+   Written by Laszlo Szekeres <lszekeres@google.com> and
+              Michal Zalewski <lcamtuf@google.com>
+
+   LLVM integration design comes from Laszlo Szekeres.
+
+   This code is the rewrite of afl-as.h's main_payload.
+*/
+
+#include "../android-ashmem.h"
+#include "../config.h"
+#include "../types.h"
+
+#include <stdio.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>
+
+/* This is a somewhat ugly hack for the experimental 'trace-pc-guard' mode.
+   Basically, we need to make sure that the forkserver is initialized after
+   the LLVM-generated runtime initialization pass, not before. */
+
+#ifdef USE_TRACE_PC
+#  define CONST_PRIO 5
+#else
+#  define CONST_PRIO 0
+#endif /* ^USE_TRACE_PC */
+
+
+/* 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;
+
+__thread u32 __afl_prev_loc;
+
+
+/* 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) {
+
+    u32 shm_id = atoi(id_str);
+
+    __afl_area_ptr = shmat(shm_id, NULL, 0);
+
+    /* 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;
+
+  /* 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) {
+
+        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(CONST_PRIO))) void __afl_auto_init(void) {
+
+  is_persistent = !!getenv(PERSIST_ENV_VAR);
+
+  if (getenv(DEFER_ENV_VAR)) return;
+
+  __afl_manual_init();
+
+}
+
+
+/* The following stuff deals with supporting -fsanitize-coverage=trace-pc-guard.
+   It remains non-operational in the traditional, plugin-backed LLVM mode.
+   For more info about 'trace-pc-guard', see README.llvm.
+
+   The first function (__sanitizer_cov_trace_pc_guard) is called back on every
+   edge (as opposed to every basic block). */
+
+void __sanitizer_cov_trace_pc_guard(uint32_t* guard) {
+  __afl_area_ptr[*guard]++;
+}
+
+
+/* Init callback. Populates instrumentation IDs. Note that we're using
+   ID of 0 as a special value to indicate non-instrumented bits. That may
+   still touch the bitmap, but in a fairly harmless way. */
+
+void __sanitizer_cov_trace_pc_guard_init(uint32_t* start, uint32_t* stop) {
+
+  u32 inst_ratio = 100;
+  u8* x;
+
+  if (start == stop || *start) return;
+
+  x = getenv("AFL_INST_RATIO");
+  if (x) inst_ratio = atoi(x);
+
+  if (!inst_ratio || inst_ratio > 100) {
+    fprintf(stderr, "[-] ERROR: Invalid AFL_INST_RATIO (must be 1-100).\n");
+    abort();
+  }
+
+  /* Make sure that the first element in the range is always set - we use that
+     to avoid duplicate calls (which can happen as an artifact of the underlying
+     implementation in LLVM). */
+
+  *(start++) = R(MAP_SIZE - 1) + 1;
+
+  while (start < stop) {
+
+    if (R(100) < inst_ratio) *start = R(MAP_SIZE - 1) + 1;
+    else *start = 0;
+
+    start++;
+
+  }
+
+}