/* american fuzzy lop++ - unicorn instrumentation ---------------------------------------------- Originally written by Andrew Griffiths and Michal Zalewski Adapted for afl-unicorn by Dominik Maier CompareCoverage and NeverZero counters by Andrea Fioraldi Copyright 2015, 2016, 2017 Google Inc. All rights reserved. Copyright 2019 AFLplusplus Project. 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 This code is a shim patched into the separately-distributed source code of Unicorn 1.0.1. It leverages the built-in QEMU tracing functionality to implement AFL-style instrumentation and to take care of the remaining parts of the AFL fork server logic. The resulting libunicorn binary is essentially a standalone instrumentation tool; for an example of how to leverage it for other purposes, you can have a look at afl-showmap.c. */ #include #include #include #include "afl-unicorn-common.h" /*************************** * VARIOUS AUXILIARY STUFF * ***************************/ /* A snippet patched into tb_find_slow to inform the parent process that we have hit a new block that hasn't been translated yet, and to tell it to translate within its own context, too (this avoids translation overhead in the next forked-off copy). */ #define AFL_UNICORN_CPU_SNIPPET1 \ do { \ \ afl_request_tsl(pc, cs_base, flags); \ \ } while (0) /* This snippet kicks in when the instruction pointer is positioned at _start and does the usual forkserver stuff, not very different from regular instrumentation injected via afl-as.h. */ #define AFL_UNICORN_CPU_SNIPPET2 \ do { \ \ if (unlikely(afl_first_instr == 0)) { \ \ afl_setup(env->uc); \ afl_forkserver(env); \ afl_first_instr = 1; \ \ } \ afl_maybe_log(env->uc, tb->pc); \ \ } while (0) /* We use one additional file descriptor to relay "needs translation" messages between the child and the fork server. */ #define TSL_FD (FORKSRV_FD - 1) /* Set in the child process in forkserver mode: */ static unsigned char afl_fork_child; static unsigned int afl_forksrv_pid; /* Function declarations. */ static void afl_setup(struct uc_struct* uc); static void afl_forkserver(CPUArchState*); static inline void afl_maybe_log(struct uc_struct* uc, unsigned long); static void afl_wait_tsl(CPUArchState*, int); static void afl_request_tsl(target_ulong, target_ulong, uint64_t); static TranslationBlock* tb_find_slow(CPUArchState*, target_ulong, target_ulong, uint64_t); /* Data structure passed around by the translate handlers: */ struct afl_tsl { target_ulong pc; target_ulong cs_base; uint64_t flags; }; /************************* * ACTUAL IMPLEMENTATION * *************************/ /* Set up SHM region and initialize other stuff. */ static void afl_setup(struct uc_struct* uc) { char *id_str = getenv(SHM_ENV_VAR), *inst_r = getenv("AFL_INST_RATIO"); int shm_id; if (inst_r) { unsigned int r; r = atoi(inst_r); if (r > 100) r = 100; if (!r) r = 1; uc->afl_inst_rms = MAP_SIZE * r / 100; } else { uc->afl_inst_rms = MAP_SIZE; } if (id_str) { shm_id = atoi(id_str); uc->afl_area_ptr = shmat(shm_id, NULL, 0); if (uc->afl_area_ptr == (void*)-1) exit(1); /* With AFL_INST_RATIO set to a low value, we want to touch the bitmap so that the parent doesn't give up on us. */ if (inst_r) uc->afl_area_ptr[0] = 1; } /* Maintain for compatibility */ if (getenv("AFL_QEMU_COMPCOV")) { uc->afl_compcov_level = 1; } if (getenv("AFL_COMPCOV_LEVEL")) { uc->afl_compcov_level = atoi(getenv("AFL_COMPCOV_LEVEL")); } } /* Fork server logic, invoked once we hit first emulated instruction. */ static void afl_forkserver(CPUArchState* env) { static unsigned char tmp[4]; if (!env->uc->afl_area_ptr) return; /* Tell the parent that we're alive. If the parent doesn't want to talk, assume that we're not running in forkserver mode. */ if (write(FORKSRV_FD + 1, tmp, 4) != 4) return; afl_forksrv_pid = getpid(); /* All right, let's await orders... */ while (1) { pid_t child_pid; int status, t_fd[2]; /* Whoops, parent dead? */ if (read(FORKSRV_FD, tmp, 4) != 4) exit(2); /* Establish a channel with child to grab translation commands. We'll read from t_fd[0], child will write to TSL_FD. */ if (pipe(t_fd) || dup2(t_fd[1], TSL_FD) < 0) exit(3); close(t_fd[1]); child_pid = fork(); if (child_pid < 0) exit(4); if (!child_pid) { /* Child process. Close descriptors and run free. */ afl_fork_child = 1; close(FORKSRV_FD); close(FORKSRV_FD + 1); close(t_fd[0]); return; } /* Parent. */ close(TSL_FD); if (write(FORKSRV_FD + 1, &child_pid, 4) != 4) exit(5); /* Collect translation requests until child dies and closes the pipe. */ afl_wait_tsl(env, t_fd[0]); /* Get and relay exit status to parent. */ if (waitpid(child_pid, &status, 0) < 0) exit(6); if (write(FORKSRV_FD + 1, &status, 4) != 4) exit(7); } } /* The equivalent of the tuple logging routine from afl-as.h. */ static inline void afl_maybe_log(struct uc_struct* uc, unsigned long cur_loc) { static __thread unsigned long prev_loc; u8* afl_area_ptr = uc->afl_area_ptr; if (!afl_area_ptr) return; /* Looks like QEMU always maps to fixed locations, so ASAN is not a concern. Phew. But instruction addresses may be aligned. Let's mangle the value to get something quasi-uniform. */ cur_loc = (cur_loc >> 4) ^ (cur_loc << 8); cur_loc &= MAP_SIZE - 1; /* Implement probabilistic instrumentation by looking at scrambled block address. This keeps the instrumented locations stable across runs. */ if (cur_loc >= uc->afl_inst_rms) return; register uintptr_t afl_idx = cur_loc ^ prev_loc; INC_AFL_AREA(afl_idx); prev_loc = cur_loc >> 1; } /* This code is invoked whenever QEMU decides that it doesn't have a translation of a particular block and needs to compute it. When this happens, we tell the parent to mirror the operation, so that the next fork() has a cached copy. */ static void afl_request_tsl(target_ulong pc, target_ulong cb, uint64_t flags) { struct afl_tsl t; if (!afl_fork_child) return; t.pc = pc; t.cs_base = cb; t.flags = flags; if (write(TSL_FD, &t, sizeof(struct afl_tsl)) != sizeof(struct afl_tsl)) return; } /* This is the other side of the same channel. Since timeouts are handled by afl-fuzz simply killing the child, we can just wait until the pipe breaks. */ static void afl_wait_tsl(CPUArchState* env, int fd) { struct afl_tsl t; while (1) { /* Broken pipe means it's time to return to the fork server routine. */ if (read(fd, &t, sizeof(struct afl_tsl)) != sizeof(struct afl_tsl)) break; tb_find_slow(env, t.pc, t.cs_base, t.flags); } close(fd); }