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/*
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Copyright 2015 Google LLC All rights reserved.
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Licensed under the Apache License, Version 2.0 (the "License");
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you may not use this file except in compliance with the License.
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You may obtain a copy of the License at:
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http://www.apache.org/licenses/LICENSE-2.0
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Unless required by applicable law or agreed to in writing, software
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distributed under the License is distributed on an "AS IS" BASIS,
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WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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See the License for the specific language governing permissions and
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limitations under the License.
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*/
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/*
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american fuzzy lop - LLVM instrumentation bootstrap
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---------------------------------------------------
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Written by Laszlo Szekeres <lszekeres@google.com> and
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Michal Zalewski <lcamtuf@google.com>
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LLVM integration design comes from Laszlo Szekeres.
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This code is the rewrite of afl-as.h's main_payload.
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*/
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#include "../android-ashmem.h"
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#include "../config.h"
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#include "../types.h"
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#include <stdio.h>
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#include <stdlib.h>
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#include <signal.h>
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#include <unistd.h>
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#include <string.h>
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#include <assert.h>
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#include <sys/mman.h>
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#include <sys/shm.h>
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#include <sys/wait.h>
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#include <sys/types.h>
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/* This is a somewhat ugly hack for the experimental 'trace-pc-guard' mode.
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Basically, we need to make sure that the forkserver is initialized after
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the LLVM-generated runtime initialization pass, not before. */
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#ifdef USE_TRACE_PC
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# define CONST_PRIO 5
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#else
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# define CONST_PRIO 0
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#endif /* ^USE_TRACE_PC */
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/* Globals needed by the injected instrumentation. The __afl_area_initial region
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is used for instrumentation output before __afl_map_shm() has a chance to run.
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It will end up as .comm, so it shouldn't be too wasteful. */
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u8 __afl_area_initial[MAP_SIZE];
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u8* __afl_area_ptr = __afl_area_initial;
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__thread u32 __afl_prev_loc;
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/* Running in persistent mode? */
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static u8 is_persistent;
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/* SHM setup. */
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static void __afl_map_shm(void) {
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u8 *id_str = getenv(SHM_ENV_VAR);
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/* If we're running under AFL, attach to the appropriate region, replacing the
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early-stage __afl_area_initial region that is needed to allow some really
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hacky .init code to work correctly in projects such as OpenSSL. */
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if (id_str) {
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u32 shm_id = atoi(id_str);
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__afl_area_ptr = shmat(shm_id, NULL, 0);
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/* Whooooops. */
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if (__afl_area_ptr == (void *)-1) _exit(1);
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/* Write something into the bitmap so that even with low AFL_INST_RATIO,
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our parent doesn't give up on us. */
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__afl_area_ptr[0] = 1;
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}
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}
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/* Fork server logic. */
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static void __afl_start_forkserver(void) {
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static u8 tmp[4];
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s32 child_pid;
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u8 child_stopped = 0;
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/* Phone home and tell the parent that we're OK. If parent isn't there,
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assume we're not running in forkserver mode and just execute program. */
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if (write(FORKSRV_FD + 1, tmp, 4) != 4) return;
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while (1) {
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u32 was_killed;
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int status;
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/* Wait for parent by reading from the pipe. Abort if read fails. */
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if (read(FORKSRV_FD, &was_killed, 4) != 4) _exit(1);
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/* If we stopped the child in persistent mode, but there was a race
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condition and afl-fuzz already issued SIGKILL, write off the old
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process. */
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if (child_stopped && was_killed) {
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child_stopped = 0;
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if (waitpid(child_pid, &status, 0) < 0) _exit(1);
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}
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if (!child_stopped) {
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/* Once woken up, create a clone of our process. */
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child_pid = fork();
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if (child_pid < 0) _exit(1);
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/* In child process: close fds, resume execution. */
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if (!child_pid) {
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close(FORKSRV_FD);
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close(FORKSRV_FD + 1);
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return;
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}
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} else {
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/* Special handling for persistent mode: if the child is alive but
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currently stopped, simply restart it with SIGCONT. */
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kill(child_pid, SIGCONT);
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child_stopped = 0;
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}
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/* In parent process: write PID to pipe, then wait for child. */
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if (write(FORKSRV_FD + 1, &child_pid, 4) != 4) _exit(1);
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if (waitpid(child_pid, &status, is_persistent ? WUNTRACED : 0) < 0)
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_exit(1);
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/* In persistent mode, the child stops itself with SIGSTOP to indicate
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a successful run. In this case, we want to wake it up without forking
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again. */
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if (WIFSTOPPED(status)) child_stopped = 1;
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/* Relay wait status to pipe, then loop back. */
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if (write(FORKSRV_FD + 1, &status, 4) != 4) _exit(1);
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}
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}
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/* A simplified persistent mode handler, used as explained in README.llvm. */
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int __afl_persistent_loop(unsigned int max_cnt) {
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static u8 first_pass = 1;
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static u32 cycle_cnt;
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if (first_pass) {
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/* Make sure that every iteration of __AFL_LOOP() starts with a clean slate.
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On subsequent calls, the parent will take care of that, but on the first
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iteration, it's our job to erase any trace of whatever happened
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before the loop. */
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if (is_persistent) {
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memset(__afl_area_ptr, 0, MAP_SIZE);
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__afl_area_ptr[0] = 1;
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__afl_prev_loc = 0;
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}
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cycle_cnt = max_cnt;
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first_pass = 0;
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return 1;
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}
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if (is_persistent) {
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if (--cycle_cnt) {
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raise(SIGSTOP);
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__afl_area_ptr[0] = 1;
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__afl_prev_loc = 0;
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return 1;
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} else {
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/* When exiting __AFL_LOOP(), make sure that the subsequent code that
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follows the loop is not traced. We do that by pivoting back to the
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dummy output region. */
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__afl_area_ptr = __afl_area_initial;
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}
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}
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return 0;
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}
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/* This one can be called from user code when deferred forkserver mode
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is enabled. */
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void __afl_manual_init(void) {
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static u8 init_done;
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if (!init_done) {
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__afl_map_shm();
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__afl_start_forkserver();
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init_done = 1;
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}
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}
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/* Proper initialization routine. */
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__attribute__((constructor(CONST_PRIO))) void __afl_auto_init(void) {
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is_persistent = !!getenv(PERSIST_ENV_VAR);
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if (getenv(DEFER_ENV_VAR)) return;
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__afl_manual_init();
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}
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/* The following stuff deals with supporting -fsanitize-coverage=trace-pc-guard.
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It remains non-operational in the traditional, plugin-backed LLVM mode.
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For more info about 'trace-pc-guard', see README.llvm.
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The first function (__sanitizer_cov_trace_pc_guard) is called back on every
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edge (as opposed to every basic block). */
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void __sanitizer_cov_trace_pc_guard(uint32_t* guard) {
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__afl_area_ptr[*guard]++;
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}
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/* Init callback. Populates instrumentation IDs. Note that we're using
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ID of 0 as a special value to indicate non-instrumented bits. That may
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still touch the bitmap, but in a fairly harmless way. */
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void __sanitizer_cov_trace_pc_guard_init(uint32_t* start, uint32_t* stop) {
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u32 inst_ratio = 100;
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u8* x;
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if (start == stop || *start) return;
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x = getenv("AFL_INST_RATIO");
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if (x) inst_ratio = atoi(x);
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if (!inst_ratio || inst_ratio > 100) {
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fprintf(stderr, "[-] ERROR: Invalid AFL_INST_RATIO (must be 1-100).\n");
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abort();
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}
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/* Make sure that the first element in the range is always set - we use that
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to avoid duplicate calls (which can happen as an artifact of the underlying
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implementation in LLVM). */
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*(start++) = R(MAP_SIZE - 1) + 1;
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while (start < stop) {
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if (R(100) < inst_ratio) *start = R(MAP_SIZE - 1) + 1;
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else *start = 0;
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start++;
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}
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}
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Loading…
Reference in new issue