* Validates ASMap structure by simulating all possible execution paths. * Ensures well-formed bytecode, valid jumps, and proper termination. */
| 235 | * Ensures well-formed bytecode, valid jumps, and proper termination. |
| 236 | */ |
| 237 | bool SanityCheckAsmap(const std::span<const std::byte> asmap, int bits) |
| 238 | { |
| 239 | size_t pos{0}; |
| 240 | const size_t endpos{asmap.size() * 8}; |
| 241 | std::vector<std::pair<uint32_t, int>> jumps; // All future positions we may jump to (bit offset in asmap -> bits to consume left) |
| 242 | jumps.reserve(bits); |
| 243 | Instruction prevopcode = Instruction::JUMP; |
| 244 | bool had_incomplete_match = false; // Track <8 bit matches for efficiency check |
| 245 | |
| 246 | while (pos != endpos) { |
| 247 | // There was a jump into the middle of the previous instruction |
| 248 | if (!jumps.empty() && pos >= jumps.back().first) return false; |
| 249 | |
| 250 | Instruction opcode = DecodeType(pos, asmap); |
| 251 | if (opcode == Instruction::RETURN) { |
| 252 | // There should not be any RETURN immediately after a DEFAULT (could be combined into just RETURN) |
| 253 | if (prevopcode == Instruction::DEFAULT) return false; |
| 254 | uint32_t asn = DecodeASN(pos, asmap); |
| 255 | if (asn == INVALID) return false; // ASN straddles EOF |
| 256 | if (jumps.empty()) { |
| 257 | // Nothing to execute anymore |
| 258 | if (endpos - pos > 7) return false; // Excessive padding |
| 259 | while (pos != endpos) { |
| 260 | if (ConsumeBitLE(pos, asmap)) return false; // Nonzero padding bit |
| 261 | } |
| 262 | return true; // Sanely reached EOF |
| 263 | } else { |
| 264 | // Continue by pretending we jumped to the next instruction |
| 265 | if (pos != jumps.back().first) return false; // Unreachable code |
| 266 | bits = jumps.back().second; // Restore the number of bits we would have had left after this jump |
| 267 | jumps.pop_back(); |
| 268 | prevopcode = Instruction::JUMP; |
| 269 | } |
| 270 | } else if (opcode == Instruction::JUMP) { |
| 271 | uint32_t jump = DecodeJump(pos, asmap); |
| 272 | if (jump == INVALID) return false; // Jump offset straddles EOF |
| 273 | if (int64_t{jump} > static_cast<int64_t>(endpos - pos)) return false; // Jump out of range |
| 274 | if (bits == 0) return false; // Consuming bits past the end of the input |
| 275 | --bits; |
| 276 | uint32_t jump_offset = pos + jump; |
| 277 | if (!jumps.empty() && jump_offset >= jumps.back().first) return false; // Intersecting jumps |
| 278 | jumps.emplace_back(jump_offset, bits); // Queue jump target for validation |
| 279 | prevopcode = Instruction::JUMP; |
| 280 | } else if (opcode == Instruction::MATCH) { |
| 281 | uint32_t match = DecodeMatch(pos, asmap); |
| 282 | if (match == INVALID) return false; // Match bits straddle EOF |
| 283 | int matchlen = std::bit_width(match) - 1; |
| 284 | if (prevopcode != Instruction::MATCH) had_incomplete_match = false; |
| 285 | // Within a sequence of matches only at most one should be incomplete |
| 286 | if (matchlen < 8 && had_incomplete_match) return false; |
| 287 | had_incomplete_match = (matchlen < 8); |
| 288 | if (bits < matchlen) return false; // Consuming bits past the end of the input |
| 289 | bits -= matchlen; |
| 290 | prevopcode = Instruction::MATCH; |
| 291 | } else if (opcode == Instruction::DEFAULT) { |
| 292 | // There should not be two successive DEFAULTs (they could be combined into one) |
| 293 | if (prevopcode == Instruction::DEFAULT) return false; |
| 294 | uint32_t asn = DecodeASN(pos, asmap); |