1  // Copyright (c) 2019-2022 The Bitcoin Core developers
  2  // Distributed under the MIT software license, see the accompanying
  3  // file COPYING or http://www.opensource.org/licenses/mit-license.php.
  4  
  5  #include <util/asmap.h>
  6  
  7  #include <clientversion.h>
  8  #include <logging.h>
  9  #include <serialize.h>
 10  #include <streams.h>
 11  #include <util/fs.h>
 12  
 13  #include <algorithm>
 14  #include <bit>
 15  #include <cassert>
 16  #include <cstdio>
 17  #include <utility>
 18  #include <vector>
 19  
 20  namespace {
 21  
 22  constexpr uint32_t INVALID = 0xFFFFFFFF;
 23  
 24  uint32_t DecodeBits(std::vector<bool>::const_iterator& bitpos, const std::vector<bool>::const_iterator& endpos, uint8_t minval, const std::vector<uint8_t> &bit_sizes)
 25  {
 26      uint32_t val = minval;
 27      bool bit;
 28      for (std::vector<uint8_t>::const_iterator bit_sizes_it = bit_sizes.begin();
 29          bit_sizes_it != bit_sizes.end(); ++bit_sizes_it) {
 30          if (bit_sizes_it + 1 != bit_sizes.end()) {
 31              if (bitpos == endpos) break;
 32              bit = *bitpos;
 33              bitpos++;
 34          } else {
 35              bit = 0;
 36          }
 37          if (bit) {
 38              val += (1 << *bit_sizes_it);
 39          } else {
 40              for (int b = 0; b < *bit_sizes_it; b++) {
 41                  if (bitpos == endpos) return INVALID; // Reached EOF in mantissa
 42                  bit = *bitpos;
 43                  bitpos++;
 44                  val += bit << (*bit_sizes_it - 1 - b);
 45              }
 46              return val;
 47          }
 48      }
 49      return INVALID; // Reached EOF in exponent
 50  }
 51  
 52  enum class Instruction : uint32_t
 53  {
 54      RETURN = 0,
 55      JUMP = 1,
 56      MATCH = 2,
 57      DEFAULT = 3,
 58  };
 59  
 60  const std::vector<uint8_t> TYPE_BIT_SIZES{0, 0, 1};
 61  Instruction DecodeType(std::vector<bool>::const_iterator& bitpos, const std::vector<bool>::const_iterator& endpos)
 62  {
 63      return Instruction(DecodeBits(bitpos, endpos, 0, TYPE_BIT_SIZES));
 64  }
 65  
 66  const std::vector<uint8_t> ASN_BIT_SIZES{15, 16, 17, 18, 19, 20, 21, 22, 23, 24};
 67  uint32_t DecodeASN(std::vector<bool>::const_iterator& bitpos, const std::vector<bool>::const_iterator& endpos)
 68  {
 69      return DecodeBits(bitpos, endpos, 1, ASN_BIT_SIZES);
 70  }
 71  
 72  
 73  const std::vector<uint8_t> MATCH_BIT_SIZES{1, 2, 3, 4, 5, 6, 7, 8};
 74  uint32_t DecodeMatch(std::vector<bool>::const_iterator& bitpos, const std::vector<bool>::const_iterator& endpos)
 75  {
 76      return DecodeBits(bitpos, endpos, 2, MATCH_BIT_SIZES);
 77  }
 78  
 79  
 80  const std::vector<uint8_t> JUMP_BIT_SIZES{5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30};
 81  uint32_t DecodeJump(std::vector<bool>::const_iterator& bitpos, const std::vector<bool>::const_iterator& endpos)
 82  {
 83      return DecodeBits(bitpos, endpos, 17, JUMP_BIT_SIZES);
 84  }
 85  
 86  }
 87  
 88  uint32_t Interpret(const std::vector<bool> &asmap, const std::vector<bool> &ip)
 89  {
 90      std::vector<bool>::const_iterator pos = asmap.begin();
 91      const std::vector<bool>::const_iterator endpos = asmap.end();
 92      uint8_t bits = ip.size();
 93      uint32_t default_asn = 0;
 94      uint32_t jump, match, matchlen;
 95      Instruction opcode;
 96      while (pos != endpos) {
 97          opcode = DecodeType(pos, endpos);
 98          if (opcode == Instruction::RETURN) {
 99              default_asn = DecodeASN(pos, endpos);
100              if (default_asn == INVALID) break; // ASN straddles EOF
101              return default_asn;
102          } else if (opcode == Instruction::JUMP) {
103              jump = DecodeJump(pos, endpos);
104              if (jump == INVALID) break; // Jump offset straddles EOF
105              if (bits == 0) break; // No input bits left
106              if (int64_t{jump} >= int64_t{endpos - pos}) break; // Jumping past EOF
107              if (ip[ip.size() - bits]) {
108                  pos += jump;
109              }
110              bits--;
111          } else if (opcode == Instruction::MATCH) {
112              match = DecodeMatch(pos, endpos);
113              if (match == INVALID) break; // Match bits straddle EOF
114              matchlen = std::bit_width(match) - 1;
115              if (bits < matchlen) break; // Not enough input bits
116              for (uint32_t bit = 0; bit < matchlen; bit++) {
117                  if ((ip[ip.size() - bits]) != ((match >> (matchlen - 1 - bit)) & 1)) {
118                      return default_asn;
119                  }
120                  bits--;
121              }
122          } else if (opcode == Instruction::DEFAULT) {
123              default_asn = DecodeASN(pos, endpos);
124              if (default_asn == INVALID) break; // ASN straddles EOF
125          } else {
126              break; // Instruction straddles EOF
127          }
128      }
129      assert(false); // Reached EOF without RETURN, or aborted (see any of the breaks above) - should have been caught by SanityCheckASMap below
130      return 0; // 0 is not a valid ASN
131  }
132  
133  bool SanityCheckASMap(const std::vector<bool>& asmap, int bits)
134  {
135      const std::vector<bool>::const_iterator begin = asmap.begin(), endpos = asmap.end();
136      std::vector<bool>::const_iterator pos = begin;
137      std::vector<std::pair<uint32_t, int>> jumps; // All future positions we may jump to (bit offset in asmap -> bits to consume left)
138      jumps.reserve(bits);
139      Instruction prevopcode = Instruction::JUMP;
140      bool had_incomplete_match = false;
141      while (pos != endpos) {
142          uint32_t offset = pos - begin;
143          if (!jumps.empty() && offset >= jumps.back().first) return false; // There was a jump into the middle of the previous instruction
144          Instruction opcode = DecodeType(pos, endpos);
145          if (opcode == Instruction::RETURN) {
146              if (prevopcode == Instruction::DEFAULT) return false; // There should not be any RETURN immediately after a DEFAULT (could be combined into just RETURN)
147              uint32_t asn = DecodeASN(pos, endpos);
148              if (asn == INVALID) return false; // ASN straddles EOF
149              if (jumps.empty()) {
150                  // Nothing to execute anymore
151                  if (endpos - pos > 7) return false; // Excessive padding
152                  while (pos != endpos) {
153                      if (*pos) return false; // Nonzero padding bit
154                      ++pos;
155                  }
156                  return true; // Sanely reached EOF
157              } else {
158                  // Continue by pretending we jumped to the next instruction
159                  offset = pos - begin;
160                  if (offset != jumps.back().first) return false; // Unreachable code
161                  bits = jumps.back().second; // Restore the number of bits we would have had left after this jump
162                  jumps.pop_back();
163                  prevopcode = Instruction::JUMP;
164              }
165          } else if (opcode == Instruction::JUMP) {
166              uint32_t jump = DecodeJump(pos, endpos);
167              if (jump == INVALID) return false; // Jump offset straddles EOF
168              if (int64_t{jump} > int64_t{endpos - pos}) return false; // Jump out of range
169              if (bits == 0) return false; // Consuming bits past the end of the input
170              --bits;
171              uint32_t jump_offset = pos - begin + jump;
172              if (!jumps.empty() && jump_offset >= jumps.back().first) return false; // Intersecting jumps
173              jumps.emplace_back(jump_offset, bits);
174              prevopcode = Instruction::JUMP;
175          } else if (opcode == Instruction::MATCH) {
176              uint32_t match = DecodeMatch(pos, endpos);
177              if (match == INVALID) return false; // Match bits straddle EOF
178              int matchlen = std::bit_width(match) - 1;
179              if (prevopcode != Instruction::MATCH) had_incomplete_match = false;
180              if (matchlen < 8 && had_incomplete_match) return false; // Within a sequence of matches only at most one should be incomplete
181              had_incomplete_match = (matchlen < 8);
182              if (bits < matchlen) return false; // Consuming bits past the end of the input
183              bits -= matchlen;
184              prevopcode = Instruction::MATCH;
185          } else if (opcode == Instruction::DEFAULT) {
186              if (prevopcode == Instruction::DEFAULT) return false; // There should not be two successive DEFAULTs (they could be combined into one)
187              uint32_t asn = DecodeASN(pos, endpos);
188              if (asn == INVALID) return false; // ASN straddles EOF
189              prevopcode = Instruction::DEFAULT;
190          } else {
191              return false; // Instruction straddles EOF
192          }
193      }
194      return false; // Reached EOF without RETURN instruction
195  }
196  
197  std::vector<bool> DecodeAsmap(fs::path path)
198  {
199      std::vector<bool> bits;
200      FILE *filestr = fsbridge::fopen(path, "rb");
201      AutoFile file{filestr};
202      if (file.IsNull()) {
203          LogPrintf("Failed to open asmap file from disk\n");
204          return bits;
205      }
206      fseek(filestr, 0, SEEK_END);
207      int length = ftell(filestr);
208      LogPrintf("Opened asmap file %s (%d bytes) from disk\n", fs::quoted(fs::PathToString(path)), length);
209      fseek(filestr, 0, SEEK_SET);
210      uint8_t cur_byte;
211      for (int i = 0; i < length; ++i) {
212          file >> cur_byte;
213          for (int bit = 0; bit < 8; ++bit) {
214              bits.push_back((cur_byte >> bit) & 1);
215          }
216      }
217      if (!SanityCheckASMap(bits, 128)) {
218          LogPrintf("Sanity check of asmap file %s failed\n", fs::quoted(fs::PathToString(path)));
219          return {};
220      }
221      return bits;
222  }
223