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83 lines
2.8 KiB
C
83 lines
2.8 KiB
C
/*
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american fuzzy lop - high-performance binary-only instrumentation
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-----------------------------------------------------------------
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Written by Andrew Griffiths <agriffiths@google.com> and
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Michal Zalewski <lcamtuf@google.com>
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Idea & design very much by Andrew Griffiths.
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TCG instrumentation and block chaining support by Andrea Biondo
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<andrea.biondo965@gmail.com>
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Copyright 2015, 2016, 2017 Google Inc. 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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This code is a shim patched into the separately-distributed source
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code of QEMU 2.10.0. It leverages the built-in QEMU tracing functionality
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to implement AFL-style instrumentation and to take care of the remaining
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parts of the AFL fork server logic.
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The resulting QEMU binary is essentially a standalone instrumentation
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tool; for an example of how to leverage it for other purposes, you can
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have a look at afl-showmap.c.
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*/
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#include "../../config.h"
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#include "tcg-op.h"
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/* Declared in afl-qemu-cpu-inl.h */
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extern unsigned char *afl_area_ptr;
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extern unsigned int afl_inst_rms;
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extern abi_ulong afl_start_code, afl_end_code;
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/* Generates TCG code for AFL's tracing instrumentation. */
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static void afl_gen_trace(target_ulong cur_loc)
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{
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static __thread target_ulong prev_loc;
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TCGv index, count, new_prev_loc;
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TCGv_ptr prev_loc_ptr, count_ptr;
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/* Optimize for cur_loc > afl_end_code, which is the most likely case on
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Linux systems. */
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if (cur_loc > afl_end_code || cur_loc < afl_start_code || !afl_area_ptr)
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return;
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/* Looks like QEMU always maps to fixed locations, so ASAN is not a
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concern. Phew. But instruction addresses may be aligned. Let's mangle
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the value to get something quasi-uniform. */
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cur_loc = (cur_loc >> 4) ^ (cur_loc << 8);
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cur_loc &= MAP_SIZE - 1;
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/* Implement probabilistic instrumentation by looking at scrambled block
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address. This keeps the instrumented locations stable across runs. */
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if (cur_loc >= afl_inst_rms) return;
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/* index = prev_loc ^ cur_loc */
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prev_loc_ptr = tcg_const_ptr(&prev_loc);
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index = tcg_temp_new();
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tcg_gen_ld_tl(index, prev_loc_ptr, 0);
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tcg_gen_xori_tl(index, index, cur_loc);
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/* afl_area_ptr[index]++ */
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count_ptr = tcg_const_ptr(afl_area_ptr);
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tcg_gen_add_ptr(count_ptr, count_ptr, TCGV_NAT_TO_PTR(index));
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count = tcg_temp_new();
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tcg_gen_ld8u_tl(count, count_ptr, 0);
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tcg_gen_addi_tl(count, count, 1);
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tcg_gen_st8_tl(count, count_ptr, 0);
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/* prev_loc = cur_loc >> 1 */
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new_prev_loc = tcg_const_tl(cur_loc >> 1);
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tcg_gen_st_tl(new_prev_loc, prev_loc_ptr, 0);
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}
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