Merge bitcoin#24214: Fix unsigned integer overflows in interpreter

bbbbaa0 Fix unsigned integer overflows in interpreter (MarcoFalke)

Pull request description:

  Unsigned integer overflow is well defined by the language and in some cases even useful or necessary. However, I think that it should be avoided in interpreter, as it makes the code harder to read and requires the whole file to be suppressed in the sanitizer. This puts more burden on reviewers to check that any changes to interpreter that involve unsigned integer overflow are sane.

  This patch involves a few changes:
  * Evaluate the addition in 64-bit "space". Previously, the first argument was `size_t` (unsigned, 32-bit or 64-bit, depending on platform) and the second was `int` (32-bit on all supported platforms). Thus the addition was done in 32-bit or 64-bit "unsigned space". Now the addition is done in 64-bit "signed space" on all platforms. This is safe because signed integer overflow (UB) isn't expected here with 64-bit integers.
  * Clarify that the value passed to the "stack macros" always fits in an `int64_t`. This is done with the C++11 syntax `int64_t{i}`, which fails to compile if `i` needs to be narrowed to fit into `int64_t`.
  * Explicitly convert the result of the addition to `size_t`. This isn't needed, because the called function already converts the value (see https://en.cppreference.com/w/cpp/container/vector/operator_at), however I have a slight preference for the explicit cast. (Happy to remove if reviewers prefer without)

  The patch does not change the bitcoind binary on my 64-bit system with `clang++ -O2`. However, it does change with gcc.

ACKs for top commit:
  achow101:
    ACK bbbbaa0
  ismaelsadeeq:
    Code review ACK bbbbaa0
  hebasto:
    ACK bbbbaa0, I have reviewed the code and it looks OK.

Tree-SHA512: 0e9cbc6a0afd3db0d1d9489fd5e32ff856217604abde370add1f01c2cae8c526f2afedeb372997217c3a70ab0f8f56442e8230f87456f8e21c9abcb7c6578f7c

src/script/interpreter.cpp

@@ -51,8 +51,8 @@ bool CastToBool(const valtype& vch)
  * Script is a stack machine (like Forth) that evaluates a predicate
  * returning a bool indicating valid or not.  There are no loops.
  */
-#define stacktop(i)  (stack.at(stack.size()+(i)))
-#define altstacktop(i)  (altstack.at(altstack.size()+(i)))
+#define stacktop(i) (stack.at(size_t(int64_t(stack.size()) + int64_t{i})))
+#define altstacktop(i) (altstack.at(size_t(int64_t(altstack.size()) + int64_t{i})))
 static inline void popstack(std::vector<valtype>& stack)
 {
     if (stack.empty())

test/sanitizer_suppressions/ubsan

@@ -55,7 +55,6 @@ unsigned-integer-overflow:MurmurHash3
 unsigned-integer-overflow:CBlockPolicyEstimator::processBlockTx
 unsigned-integer-overflow:TxConfirmStats::EstimateMedianVal
 unsigned-integer-overflow:prevector.h
-unsigned-integer-overflow:EvalScript
 unsigned-integer-overflow:InsecureRandomContext::rand64
 unsigned-integer-overflow:InsecureRandomContext::SplitMix64
 unsigned-integer-overflow:bitset_detail::PopCount