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negate after converting to unsigned to avoid UB on minimum signed value #1526

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merged 4 commits into from
Aug 22, 2023
Merged

negate after converting to unsigned to avoid UB on minimum signed value #1526

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7439516
negate after converting to unsigned to avoid UB on min value
spoonincode Aug 17, 2023
614b005
add a comment on negating after conversion to unsigned
spoonincode Aug 21, 2023
f68377f
two more negations that should go after unsigned conversion
spoonincode Aug 21, 2023
ff528b6
remove now redundant signed cast
spoonincode Aug 22, 2023
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3 changes: 2 additions & 1 deletion libraries/chain/webassembly/console.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -46,8 +46,9 @@ namespace eosio { namespace chain { namespace webassembly {
bool is_negative = (*val < 0);
unsigned __int128 val_magnitude;

// negate after conversion to unsigned to avoid possible integer overflow
if( is_negative )
val_magnitude = static_cast<unsigned __int128>(-*val); // Works even if val is at the lowest possible value of a int128_t
val_magnitude = -static_cast<unsigned __int128>(*val); // Works even if val is at the lowest possible value of a int128_t
else
val_magnitude = static_cast<unsigned __int128>(*val);

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4 changes: 2 additions & 2 deletions libraries/wasm-jit/Source/WAST/ParseNumbers.cpp
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Expand Up @@ -229,7 +229,7 @@ bool tryParseInt(ParseState& state,UnsignedInt& outUnsignedInt,I64 minSignedValu
{
case t_decimalInt:
isNegative = parseSign(nextChar);
u64 = parseDecimalUnsignedInt(nextChar,state,isNegative ? U64(-minSignedValue) : maxUnsignedValue,"int literal");
u64 = parseDecimalUnsignedInt(nextChar,state,isNegative ? -U64(minSignedValue) : maxUnsignedValue,"int literal");
break;
case t_hexInt:
isNegative = parseSign(nextChar);
Expand All @@ -239,7 +239,7 @@ bool tryParseInt(ParseState& state,UnsignedInt& outUnsignedInt,I64 minSignedValu
return false;
};

outUnsignedInt = isNegative ? UnsignedInt(-I64(u64)) : UnsignedInt(u64);
outUnsignedInt = isNegative ? -UnsignedInt(u64) : UnsignedInt(u64);

++state.nextToken;
WAVM_ASSERT_THROW(nextChar <= state.string + state.nextToken->begin);
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