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Differential D4834 Diff 15923 src/script/scriptcache.cpp

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src/script/scriptcache.cpp

// Copyright (c) 2017 The Bitcoin developers // Copyright (c) 2017 The Bitcoin developers
// Distributed under the MIT software license, see the accompanying // Distributed under the MIT software license, see the accompanying
// file COPYING or http://www.opensource.org/licenses/mit-license.php. // file COPYING or http://www.opensource.org/licenses/mit-license.php.
#include <script/scriptcache.h> #include <script/scriptcache.h>
#include <crypto/sha256.h> #include <crypto/sha256.h>
#include <cuckoocache.h> #include <cuckoocache.h>
#include <primitives/transaction.h> #include <primitives/transaction.h>
#include <random.h> #include <random.h>
#include <script/sigcache.h> #include <script/sigcache.h>
#include <sync.h> #include <sync.h>
#include <util/system.h> #include <util/system.h>
#include <validation.h> #include <validation.h>
static CuckooCache::cache<CuckooCache::KeyOnly<uint256>, SignatureCacheHasher> #include <limits>
/**
* In future if many more values are added, it should be considered to
* expand the element size to 64 bytes (with padding the spare space as
* needed) so the key can be long. Shortening the key too much risks
* opening ourselves up to consensus-failing collisions, however it should
* be noted that our cache nonce is private and unique, so collisions would
* affect only one node and attackers have no way of offline-preparing a
* collision attack even on short keys.
*/
struct ScriptCacheElement {
using KeyType = ScriptCacheKey;
KeyType key;
int nSigChecks;
ScriptCacheElement() = default;
ScriptCacheElement(const KeyType &keyIn, int nSigChecksIn)
: key(keyIn), nSigChecks(nSigChecksIn) {}
const KeyType &getKey() const { return key; }
};
static_assert(sizeof(ScriptCacheElement) == 32,
"ScriptCacheElement should be 32 bytes");
class ScriptCacheHasher {
public:
template <uint8_t hash_select>
uint32_t operator()(const ScriptCacheKey &k) const {
static_assert(hash_select < 8, "only has 8 hashes available.");
const auto &d = k.data;
static_assert(sizeof(d) == 28,
"modify the following if key size changes");
uint32_t u;
static_assert(sizeof(u) == 4 && sizeof(d[0]) == 1, "basic assumptions");
if (hash_select < 7) {
std::memcpy(&u, d.data() + 4 * hash_select, 4);
} else {
// We are required to produce 8 subhashes, and all bytes have
// been used once. We re-use the bytes but mix together different
// entries (and flip the order) to get a new, distinct value.
uint8_t arr[4];
arr[0] = d[3] ^ d[7] ^ d[11] ^ d[15];
arr[1] = d[6] ^ d[10] ^ d[14] ^ d[18];
arr[2] = d[9] ^ d[13] ^ d[17] ^ d[21];
arr[3] = d[12] ^ d[16] ^ d[20] ^ d[24];
std::memcpy(&u, arr, 4);
}
return u;
}
};
static CuckooCache::cache<ScriptCacheElement, ScriptCacheHasher>
scriptExecutionCache; scriptExecutionCache;
static uint256 scriptExecutionCacheNonce(GetRandHash()); static uint256 scriptExecutionCacheNonce(GetRandHash());
void InitScriptExecutionCache() { void InitScriptExecutionCache() {
// nMaxCacheSize is unsigned. If -maxscriptcachesize is set to zero, // nMaxCacheSize is unsigned. If -maxscriptcachesize is set to zero,
// setup_bytes creates the minimum possible cache (2 elements). // setup_bytes creates the minimum possible cache (2 elements).
size_t nMaxCacheSize = size_t nMaxCacheSize =
std::min( std::min(
std::max(int64_t(0), gArgs.GetArg("-maxscriptcachesize", std::max(int64_t(0), gArgs.GetArg("-maxscriptcachesize",
DEFAULT_MAX_SCRIPT_CACHE_SIZE)), DEFAULT_MAX_SCRIPT_CACHE_SIZE)),
MAX_MAX_SCRIPT_CACHE_SIZE) * MAX_MAX_SCRIPT_CACHE_SIZE) *
(size_t(1) << 20); (size_t(1) << 20);
size_t nElems = scriptExecutionCache.setup_bytes(nMaxCacheSize); size_t nElems = scriptExecutionCache.setup_bytes(nMaxCacheSize);
LogPrintf("Using %zu MiB out of %zu requested for script execution cache, " LogPrintf("Using %zu MiB out of %zu requested for script execution cache, "
"able to store %zu elements\n", "able to store %zu elements\n",
(nElems * sizeof(uint256)) >> 20, nMaxCacheSize >> 20, nElems); (nElems * sizeof(uint256)) >> 20, nMaxCacheSize >> 20, nElems);
} }
uint256 GetScriptCacheKey(const CTransaction &tx, uint32_t flags) { ScriptCacheKey::ScriptCacheKey(const CTransaction &tx, uint32_t flags) {
uint256 key; std::array<uint8_t, 32> hash;
// We only use the first 19 bytes of nonce to avoid a second SHA round - // We only use the first 19 bytes of nonce to avoid a second SHA round -
// giving us 19 + 32 + 4 = 55 bytes (+ 8 + 1 = 64) // giving us 19 + 32 + 4 = 55 bytes (+ 8 + 1 = 64)
static_assert(55 - sizeof(flags) - 32 >= 128 / 8, static_assert(55 - sizeof(flags) - 32 >= 128 / 8,
"Want at least 128 bits of nonce for script execution cache"); "Want at least 128 bits of nonce for script execution cache");
CSHA256() CSHA256()
.Write(scriptExecutionCacheNonce.begin(), 55 - sizeof(flags) - 32) .Write(scriptExecutionCacheNonce.begin(), 55 - sizeof(flags) - 32)
.Write(tx.GetHash().begin(), 32) .Write(tx.GetHash().begin(), 32)
.Write((uint8_t *)&flags, sizeof(flags)) .Write((uint8_t *)&flags, sizeof(flags))
.Finalize(key.begin()); .Finalize(hash.begin());
return key; assert(data.size() < hash.size());
std::copy(hash.begin(), hash.begin() + data.size(), data.begin());
} }
bool IsKeyInScriptCache(uint256 key, bool erase) { bool IsKeyInScriptCache(ScriptCacheKey key, bool erase, int &nSigChecksOut) {
// TODO: Remove this requirement by making CuckooCache not require external // TODO: Remove this requirement by making CuckooCache not require external
// locks // locks
AssertLockHeld(cs_main); AssertLockHeld(cs_main);
return scriptExecutionCache.contains(key, erase);
ScriptCacheElement elem(key, 0);
bool ret = scriptExecutionCache.get(elem, erase);
nSigChecksOut = elem.nSigChecks;
return ret;
} }
void AddKeyInScriptCache(uint256 key) { void AddKeyInScriptCache(ScriptCacheKey key, int nSigChecks) {
// TODO: Remove this requirement by making CuckooCache not require external // TODO: Remove this requirement by making CuckooCache not require external
// locks // locks
AssertLockHeld(cs_main); AssertLockHeld(cs_main);
scriptExecutionCache.insert(key);
ScriptCacheElement elem(key, nSigChecks);
scriptExecutionCache.insert(elem);
} }