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// 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;
bool bit;
for (std::vector<uint8_t>::const_iterator bit_sizes_it = bit_sizes.begin();
bit_sizes_it != bit_sizes.end(); ++bit_sizes_it) {
if (bit_sizes_it + 1 != bit_sizes.end()) {
if (bitpos == endpos) break;
bit = *bitpos;
bitpos++;
} else {
bit = 0;
}
if (bit) {
val += (1 << *bit_sizes_it);
} else {
for (int b = 0; b < *bit_sizes_it; b++) {
if (bitpos == endpos) return INVALID; // Reached EOF in mantissa
bit = *bitpos;
bitpos++;
val += bit << (*bit_sizes_it - 1 - b);
}
return val;
}
}
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};
Instruction DecodeType(std::vector<bool>::const_iterator& bitpos, const std::vector<bool>::const_iterator& endpos)
{
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};
uint32_t DecodeASN(std::vector<bool>::const_iterator& bitpos, const std::vector<bool>::const_iterator& endpos)
{
return DecodeBits(bitpos, endpos, 1, ASN_BIT_SIZES);
}
const std::vector<uint8_t> MATCH_BIT_SIZES{1, 2, 3, 4, 5, 6, 7, 8};
uint32_t DecodeMatch(std::vector<bool>::const_iterator& bitpos, const std::vector<bool>::const_iterator& endpos)
{
return DecodeBits(bitpos, endpos, 2, MATCH_BIT_SIZES);
}
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};
uint32_t DecodeJump(std::vector<bool>::const_iterator& bitpos, const std::vector<bool>::const_iterator& endpos)
{
return DecodeBits(bitpos, endpos, 17, JUMP_BIT_SIZES);
}
}
uint32_t Interpret(const std::vector<bool> &asmap, const std::vector<bool> &ip)
{
std::vector<bool>::const_iterator pos = asmap.begin();
const std::vector<bool>::const_iterator endpos = asmap.end();
uint8_t bits = ip.size();
uint32_t default_asn = 0;
uint32_t jump, match, matchlen;
Instruction opcode;
while (pos != endpos) {
opcode = DecodeType(pos, endpos);
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 (jump == INVALID) break; // Jump offset straddles EOF
if (bits == 0) break; // No input bits left
if (int64_t{jump} >= int64_t{endpos - pos}) break; // Jumping past EOF
if (ip[ip.size() - bits]) {
pos += jump;
}
bits--;
} 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 ((ip[ip.size() - bits]) != ((match >> (matchlen - 1 - bit)) & 1)) {
return default_asn;
}
bits--;
}
} else if (opcode == Instruction::DEFAULT) {
default_asn = DecodeASN(pos, endpos);
if (default_asn == INVALID) break; // ASN straddles EOF
} else {
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 (int64_t{jump} > int64_t{endpos - pos}) 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
}
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