diff options
Diffstat (limited to 'src/util/asmap.cpp')
| -rw-r--r-- | src/util/asmap.cpp | 114 |
1 files changed, 99 insertions, 15 deletions
diff --git a/src/util/asmap.cpp b/src/util/asmap.cpp index 60bd27bf90..bd77d74218 100644 --- a/src/util/asmap.cpp +++ b/src/util/asmap.cpp @@ -1,13 +1,16 @@ -// Copyright (c) 2019 The Bitcoin Core developers +// Copyright (c) 2019-2020 The Bitcoin Core developers // Distributed under the MIT software license, see the accompanying // file COPYING or http://www.opensource.org/licenses/mit-license.php. +#include <map> #include <vector> #include <assert.h> #include <crypto/common.h> namespace { +constexpr uint32_t INVALID = 0xFFFFFFFF; + 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) { uint32_t val = minval; @@ -25,7 +28,7 @@ uint32_t DecodeBits(std::vector<bool>::const_iterator& bitpos, const std::vector val += (1 << *bit_sizes_it); } else { for (int b = 0; b < *bit_sizes_it; b++) { - if (bitpos == endpos) break; + if (bitpos == endpos) return INVALID; // Reached EOF in mantissa bit = *bitpos; bitpos++; val += bit << (*bit_sizes_it - 1 - b); @@ -33,13 +36,21 @@ uint32_t DecodeBits(std::vector<bool>::const_iterator& bitpos, const std::vector return val; } } - return -1; + return INVALID; // Reached EOF in exponent } +enum class Instruction : uint32_t +{ + RETURN = 0, + JUMP = 1, + MATCH = 2, + DEFAULT = 3, +}; + const std::vector<uint8_t> TYPE_BIT_SIZES{0, 0, 1}; -uint32_t DecodeType(std::vector<bool>::const_iterator& bitpos, const std::vector<bool>::const_iterator& endpos) +Instruction DecodeType(std::vector<bool>::const_iterator& bitpos, const std::vector<bool>::const_iterator& endpos) { - return DecodeBits(bitpos, endpos, 0, TYPE_BIT_SIZES); + return Instruction(DecodeBits(bitpos, endpos, 0, TYPE_BIT_SIZES)); } const std::vector<uint8_t> ASN_BIT_SIZES{15, 16, 17, 18, 19, 20, 21, 22, 23, 24}; @@ -70,34 +81,107 @@ uint32_t Interpret(const std::vector<bool> &asmap, const std::vector<bool> &ip) const std::vector<bool>::const_iterator endpos = asmap.end(); uint8_t bits = ip.size(); uint32_t default_asn = 0; - uint32_t opcode, jump, match, matchlen; + uint32_t jump, match, matchlen; + Instruction opcode; while (pos != endpos) { opcode = DecodeType(pos, endpos); - if (opcode == 0) { - return DecodeASN(pos, endpos); - } else if (opcode == 1) { + if (opcode == Instruction::RETURN) { + default_asn = DecodeASN(pos, endpos); + if (default_asn == INVALID) break; // ASN straddles EOF + return default_asn; + } else if (opcode == Instruction::JUMP) { jump = DecodeJump(pos, endpos); - if (bits == 0) break; + if (jump == INVALID) break; // Jump offset straddles EOF + if (bits == 0) break; // No input bits left + if (pos + jump < pos) break; // overflow + if (pos + jump >= endpos) break; // Jumping past EOF if (ip[ip.size() - bits]) { - if (jump >= endpos - pos) break; pos += jump; } bits--; - } else if (opcode == 2) { + } else if (opcode == Instruction::MATCH) { match = DecodeMatch(pos, endpos); + if (match == INVALID) break; // Match bits straddle EOF matchlen = CountBits(match) - 1; + if (bits < matchlen) break; // Not enough input bits for (uint32_t bit = 0; bit < matchlen; bit++) { - if (bits == 0) break; if ((ip[ip.size() - bits]) != ((match >> (matchlen - 1 - bit)) & 1)) { return default_asn; } bits--; } - } else if (opcode == 3) { + } else if (opcode == Instruction::DEFAULT) { default_asn = DecodeASN(pos, endpos); + if (default_asn == INVALID) break; // ASN straddles EOF } else { - break; + break; // Instruction straddles EOF } } + assert(false); // Reached EOF without RETURN, or aborted (see any of the breaks above) - should have been caught by SanityCheckASMap below return 0; // 0 is not a valid ASN } + +bool SanityCheckASMap(const std::vector<bool>& asmap, int bits) +{ + const std::vector<bool>::const_iterator begin = asmap.begin(), endpos = asmap.end(); + std::vector<bool>::const_iterator pos = begin; + std::vector<std::pair<uint32_t, int>> jumps; // All future positions we may jump to (bit offset in asmap -> bits to consume left) + jumps.reserve(bits); + Instruction prevopcode = Instruction::JUMP; + bool had_incomplete_match = false; + while (pos != endpos) { + uint32_t offset = pos - begin; + if (!jumps.empty() && offset >= jumps.back().first) return false; // There was a jump into the middle of the previous instruction + Instruction opcode = DecodeType(pos, endpos); + if (opcode == Instruction::RETURN) { + if (prevopcode == Instruction::DEFAULT) return false; // There should not be any RETURN immediately after a DEFAULT (could be combined into just RETURN) + uint32_t asn = DecodeASN(pos, endpos); + if (asn == INVALID) return false; // ASN straddles EOF + if (jumps.empty()) { + // Nothing to execute anymore + if (endpos - pos > 7) return false; // Excessive padding + while (pos != endpos) { + if (*pos) return false; // Nonzero padding bit + ++pos; + } + return true; // Sanely reached EOF + } else { + // Continue by pretending we jumped to the next instruction + offset = pos - begin; + if (offset != jumps.back().first) return false; // Unreachable code + bits = jumps.back().second; // Restore the number of bits we would have had left after this jump + jumps.pop_back(); + prevopcode = Instruction::JUMP; + } + } else if (opcode == Instruction::JUMP) { + uint32_t jump = DecodeJump(pos, endpos); + if (jump == INVALID) return false; // Jump offset straddles EOF + if (pos + jump < pos) return false; // overflow + if (pos + jump > endpos) return false; // Jump out of range + if (bits == 0) return false; // Consuming bits past the end of the input + --bits; + uint32_t jump_offset = pos - begin + jump; + if (!jumps.empty() && jump_offset >= jumps.back().first) return false; // Intersecting jumps + jumps.emplace_back(jump_offset, bits); + prevopcode = Instruction::JUMP; + } else if (opcode == Instruction::MATCH) { + uint32_t match = DecodeMatch(pos, endpos); + if (match == INVALID) return false; // Match bits straddle EOF + int matchlen = CountBits(match) - 1; + if (prevopcode != Instruction::MATCH) had_incomplete_match = false; + if (matchlen < 8 && had_incomplete_match) return false; // Within a sequence of matches only at most one should be incomplete + had_incomplete_match = (matchlen < 8); + if (bits < matchlen) return false; // Consuming bits past the end of the input + bits -= matchlen; + prevopcode = Instruction::MATCH; + } else if (opcode == Instruction::DEFAULT) { + if (prevopcode == Instruction::DEFAULT) return false; // There should not be two successive DEFAULTs (they could be combined into one) + uint32_t asn = DecodeASN(pos, endpos); + if (asn == INVALID) return false; // ASN straddles EOF + prevopcode = Instruction::DEFAULT; + } else { + return false; // Instruction straddles EOF + } + } + return false; // Reached EOF without RETURN instruction +} |