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Fix validation of unused LEB128 bits #6680

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Merged
tlively merged 2 commits into from
Jun 19, 2024
Merged

Fix validation of unused LEB128 bits #6680

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32a67bf
Fix validation of unused LEB128 bits
tlively Jun 18, 2024
5c8bd00
127
tlively Jun 18, 2024
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1 change: 0 additions & 1 deletion scripts/test/shared.py
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Original file line number Diff line number Diff line change
Expand Up @@ -400,7 +400,6 @@ def get_tests(test_dir, extensions=[], recursive=False):
# expected-output/ if any.
SPEC_TESTS_TO_SKIP = [
# Malformed module accepted
'binary-leb128.wast',
'utf8-custom-section-id.wast',
'utf8-import-field.wast',
'utf8-import-module.wast',
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27 changes: 16 additions & 11 deletions src/wasm-binary.h
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Expand Up @@ -102,16 +102,22 @@ template<typename T, typename MiniT> struct LEB {
bool last = !(byte & 128);
T payload = byte & 127;
using mask_type = typename std::make_unsigned<T>::type;
auto shift_mask = 0 == shift
? ~mask_type(0)
: ((mask_type(1) << (sizeof(T) * 8 - shift)) - 1u);
T significant_payload = payload & shift_mask;
if (significant_payload != payload) {
if (!(std::is_signed<T>::value && last)) {
throw ParseException("LEB dropped bits only valid for signed LEB");
auto payload_mask = 0 == shift
? ~mask_type(0)
: ((mask_type(1) << (sizeof(T) * 8 - shift)) - 1u);
T significant_payload = payload_mask & payload;
value |= significant_payload << shift;
T unused_bits_mask = ~payload_mask & 127;
T unused_bits = payload & unused_bits_mask;
if (std::is_signed_v<T> && value < 0) {
if (unused_bits != unused_bits_mask) {
throw ParseException("Unused negative LEB bits must be 1s");
}
} else {
if (unused_bits != 0) {
throw ParseException("Unused non-negative LEB bits must be 0s");
}
}
value |= significant_payload << shift;
if (last) {
break;
}
Expand All @@ -120,9 +126,8 @@ template<typename T, typename MiniT> struct LEB {
throw ParseException("LEB overflow");
}
}
// If signed LEB, then we might need to sign-extend. (compile should
// optimize this out if not needed).
if (std::is_signed<T>::value) {
// If signed LEB, then we might need to sign-extend.
if constexpr (std::is_signed_v<T>) {
shift += 7;
if ((byte & 64) && size_t(shift) < 8 * sizeof(T)) {
size_t sext_bits = 8 * sizeof(T) - size_t(shift);
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