diff --git a/afl-qemu-cpu-inl.h b/afl-qemu-cpu-inl.h new file mode 100644 index 0000000..beea1bc --- /dev/null +++ b/afl-qemu-cpu-inl.h @@ -0,0 +1,313 @@ +/* + 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 - high-performance binary-only instrumentation + ----------------------------------------------------------------- + + Written by Andrew Griffiths and + Michal Zalewski + + Idea & design very much by Andrew Griffiths. + + This code is a shim patched into the separately-distributed source + code of QEMU 2.10.0. 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 QEMU 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 "../../config.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_QEMU_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_QEMU_CPU_SNIPPET2 do { \ + if(itb->pc == afl_entry_point) { \ + afl_setup(); \ + afl_forkserver(cpu); \ + } \ + afl_maybe_log(itb->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) + +/* This is equivalent to afl-as.h: */ + +static unsigned char *afl_area_ptr; + +/* Exported variables populated by the code patched into elfload.c: */ + +abi_ulong afl_entry_point, /* ELF entry point (_start) */ + afl_start_code, /* .text start pointer */ + afl_end_code; /* .text end pointer */ + +/* Set in the child process in forkserver mode: */ + +static unsigned char afl_fork_child; +unsigned int afl_forksrv_pid; + +/* Instrumentation ratio: */ + +static unsigned int afl_inst_rms = MAP_SIZE; + +/* Function declarations. */ + +static void afl_setup(void); +static void afl_forkserver(CPUState*); +static inline void afl_maybe_log(abi_ulong); + +static void afl_wait_tsl(CPUState*, int); +static void afl_request_tsl(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; +}; + +/* Some forward decls: */ + +TranslationBlock *tb_htable_lookup(CPUState*, target_ulong, target_ulong, uint32_t); +static inline TranslationBlock *tb_find(CPUState*, TranslationBlock*, int); + +/************************* + * ACTUAL IMPLEMENTATION * + *************************/ + +/* Set up SHM region and initialize other stuff. */ + +static void afl_setup(void) { + + 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; + + afl_inst_rms = MAP_SIZE * r / 100; + + } + + if (id_str) { + + shm_id = atoi(id_str); + afl_area_ptr = shmat(shm_id, NULL, 0); + + if (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) afl_area_ptr[0] = 1; + + + } + + if (getenv("AFL_INST_LIBS")) { + + afl_start_code = 0; + afl_end_code = (abi_ulong)-1; + + } + + /* pthread_atfork() seems somewhat broken in util/rcu.c, and I'm + not entirely sure what is the cause. This disables that + behaviour, and seems to work alright? */ + + rcu_disable_atfork(); + +} + + +/* Fork server logic, invoked once we hit _start. */ + +static void afl_forkserver(CPUState *cpu) { + + static unsigned char tmp[4]; + + if (!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(cpu, 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(abi_ulong cur_loc) { + + static __thread abi_ulong prev_loc; + + /* Optimize for cur_loc > afl_end_code, which is the most likely case on + Linux systems. */ + + if (cur_loc > afl_end_code || cur_loc < afl_start_code || !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 >= afl_inst_rms) return; + + afl_area_ptr[cur_loc ^ prev_loc]++; + 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(CPUState *cpu, int fd) { + + struct afl_tsl t; + TranslationBlock *tb; + + 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 = tb_htable_lookup(cpu, t.pc, t.cs_base, t.flags); + + if(!tb) { + mmap_lock(); + tb_lock(); + tb_gen_code(cpu, t.pc, t.cs_base, t.flags, 0); + mmap_unlock(); + tb_unlock(); + } + + } + + close(fd); + +}