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baseline: Better stack overflow/underflow checks #518

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merged 3 commits into from
Nov 5, 2022
Merged

baseline: Better stack overflow/underflow checks #518

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a668244
baseline: Simplify static_assert condition
chfast Oct 26, 2022
7fad7aa
baseline: Move stack size computation to check_requirements()
chfast Oct 26, 2022
f18d1f7
baseline: Better stack overflow/underflow checks
chfast Oct 26, 2022
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29 changes: 17 additions & 12 deletions lib/evmone/baseline.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -93,18 +93,20 @@ namespace
/// - if stack height requirements are fulfilled (stack overflow, stack underflow)
/// - charges the instruction base gas cost and checks is there is any gas left.
///
/// @tparam Op Instruction opcode.
/// @param cost_table Table of base gas costs.
/// @param [in,out] gas_left Gas left.
/// @param stack_size Current stack height.
/// @tparam Op Instruction opcode.
/// @param cost_table Table of base gas costs.
/// @param [in,out] gas_left Gas left.
/// @param stack_top Pointer to the stack top item.
/// @param stack_bottom Pointer to the stack bottom.
/// The stack height is stack_top - stack_bottom.
/// @return Status code with information which check has failed
/// or EVMC_SUCCESS if everything is fine.
template <evmc_opcode Op>
inline evmc_status_code check_requirements(
const CostTable& cost_table, int64_t& gas_left, ptrdiff_t stack_size) noexcept
inline evmc_status_code check_requirements(const CostTable& cost_table, int64_t& gas_left,
const uint256* stack_top, const uint256* stack_bottom) noexcept
{
static_assert(
!(instr::has_const_gas_cost(Op) && instr::gas_costs[EVMC_FRONTIER][Op] == instr::undefined),
!instr::has_const_gas_cost(Op) || instr::gas_costs[EVMC_FRONTIER][Op] != instr::undefined,
"undefined instructions must not be handled by check_requirements()");

auto gas_cost = instr::gas_costs[EVMC_FRONTIER][Op]; // Init assuming const cost.
Expand All @@ -122,13 +124,16 @@ inline evmc_status_code check_requirements(
// but it is nicer because complete gas check may need to inspect operands.
if constexpr (instr::traits[Op].stack_height_change > 0)
{
static_assert(instr::traits[Op].stack_height_change == 1);
if (INTX_UNLIKELY(stack_size == StackSpace::limit))
static_assert(instr::traits[Op].stack_height_change == 1,
"unexpected instruction with multiple results");
if (INTX_UNLIKELY(stack_top == stack_bottom + StackSpace::limit))
return EVMC_STACK_OVERFLOW;
}
if constexpr (instr::traits[Op].stack_height_required > 0)
{
if (INTX_UNLIKELY(stack_size < instr::traits[Op].stack_height_required))
// Check stack underflow using pointer comparison <= (better optimization).
static constexpr auto min_offset = instr::traits[Op].stack_height_required - 1;
if (INTX_UNLIKELY(stack_top <= stack_bottom + min_offset))
return EVMC_STACK_UNDERFLOW;
}

Expand Down Expand Up @@ -202,8 +207,8 @@ template <evmc_opcode Op>
[[release_inline]] inline Position invoke(const CostTable& cost_table, const uint256* stack_bottom,
Position pos, ExecutionState& state) noexcept
{
const auto stack_size = pos.stack_top - stack_bottom;
if (const auto status = check_requirements<Op>(cost_table, state.gas_left, stack_size);
if (const auto status =
check_requirements<Op>(cost_table, state.gas_left, pos.stack_top, stack_bottom);
status != EVMC_SUCCESS)
{
state.status = status;
Expand Down