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Fix modexp exponent EIP-7823 limit check #1294

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Merged
chfast merged 1 commit into from
Aug 15, 2025
Merged

Fix modexp exponent EIP-7823 limit check #1294

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15 changes: 11 additions & 4 deletions test/state/precompiles.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -168,14 +168,21 @@ PrecompileAnalysis expmod_analyze(bytes_view input, evmc_revision rev) noexcept
const auto exp_len256 = be::unsafe::load<uint256>(&input_header[32]);
const auto mod_len256 = be::unsafe::load<uint256>(&input_header[64]);

if (base_len256 == 0 && mod_len256 == 0)
return {min_gas, 0};

// Check the declared input lengths against the practical (2**32)
// or specified (EIP-7823: 2**10) limits.
const auto len_limit =
rev < EVMC_OSAKA ? std::numeric_limits<uint32_t>::max() : MODEXP_LEN_LIMIT_EIP7823;
if (base_len256 > len_limit || exp_len256 > len_limit || mod_len256 > len_limit)
if (base_len256 > len_limit || mod_len256 > len_limit)
return {GasCostMax, 0};

if (exp_len256 > len_limit)
{
// Before EIP-7823, the big exponent may be canceled with zero multiplication complexity.
if (rev < EVMC_OSAKA && base_len256 == 0 && mod_len256 == 0)
return {min_gas, 0};
return {GasCostMax, 0};
}

const auto base_len = static_cast<uint32_t>(base_len256);
const auto exp_len = static_cast<uint32_t>(exp_len256);
const auto mod_len = static_cast<uint32_t>(mod_len256);
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3 changes: 3 additions & 0 deletions test/unittests/precompiles_expmod_test.cpp
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Expand Up @@ -182,6 +182,9 @@ TEST(expmod, incomplete_inputs)
{"0000000000000000000000000000000000000000000000000000000000000001 0000000000000000000000000000000000000000000000000000000000000001 0000000000000000000000000000000000000000000000000000000000000003 ba ee 000000 fe", "000000"},
{"0000000000000000000000000000000000000000000000000000000000000010 0000000000000000000000000000000000000000000000000000000000000010 0000000000000000000000000000000000000000000000000000000000000001 0000000000000000000000000000000001", "00"},
{"000000000000000000000000000000000000000000000000000000000000ffff 0000000000000000000000000000000000000000000000000000000000000001 0000000000000000000000000000000000000000000000000000000000000001 80", "00"},
{"0000000000000000000000000000000000000000000000000000000000000000 0000000000000000000000000000000000000000000000000000000000000001 0000000000000000000000000000000000000000000000000000000000000000", ""},
{"0000000000000000000000000000000000000000000000000000000000000000 0000000000000000000000000000000000000000000000000000000000000002 0000000000000000000000000000000000000000000000000000000000000000 80", ""},
{"0000000000000000000000000000000000000000000000000000000000000000 0000000000000000000000000000000000000000000000000000000100000000 0000000000000000000000000000000000000000000000000000000000000000 80", ""},
// clang-format on
};

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