solidity/libsolidity/formal/CHC.h
2021-03-30 17:55:21 +02:00

382 lines
15 KiB
C++

/*
This file is part of solidity.
solidity is free software: you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation, either version 3 of the License, or
(at your option) any later version.
solidity is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with solidity. If not, see <http://www.gnu.org/licenses/>.
*/
// SPDX-License-Identifier: GPL-3.0
/**
* Model checker based on Constrained Horn Clauses.
*
* A Solidity contract's CFG is encoded into a system of Horn clauses where
* each block has a predicate and edges are rules.
*
* The entry block is the constructor which has no in-edges.
* The constructor has one out-edge to an artificial block named _Interface_
* which has in/out-edges from/to all public functions.
*
* Loop invariants for Interface -> Interface' are state invariants.
*/
#pragma once
#include <libsolidity/formal/ModelCheckerSettings.h>
#include <libsolidity/formal/Predicate.h>
#include <libsolidity/formal/SMTEncoder.h>
#include <libsolidity/interface/ReadFile.h>
#include <libsmtutil/CHCSolverInterface.h>
#include <boost/algorithm/string/join.hpp>
#include <map>
#include <optional>
#include <set>
namespace solidity::frontend
{
class CHC: public SMTEncoder
{
public:
CHC(
smt::EncodingContext& _context,
langutil::ErrorReporter& _errorReporter,
std::map<util::h256, std::string> const& _smtlib2Responses,
ReadCallback::Callback const& _smtCallback,
smtutil::SMTSolverChoice _enabledSolvers,
ModelCheckerSettings const& _settings
);
void analyze(SourceUnit const& _sources);
std::map<ASTNode const*, std::set<VerificationTargetType>> const& safeTargets() const { return m_safeTargets; }
std::map<ASTNode const*, std::set<VerificationTargetType>> const& unsafeTargets() const { return m_unsafeTargets; }
/// This is used if the Horn solver is not directly linked into this binary.
/// @returns a list of inputs to the Horn solver that were not part of the argument to
/// the constructor.
std::vector<std::string> unhandledQueries() const;
private:
/// Visitor functions.
//@{
bool visit(ContractDefinition const& _node) override;
void endVisit(ContractDefinition const& _node) override;
bool visit(FunctionDefinition const& _node) override;
void endVisit(FunctionDefinition const& _node) override;
bool visit(Block const& _block) override;
void endVisit(Block const& _block) override;
bool visit(IfStatement const& _node) override;
bool visit(WhileStatement const&) override;
bool visit(ForStatement const&) override;
void endVisit(ForStatement const&) override;
void endVisit(FunctionCall const& _node) override;
void endVisit(Break const& _node) override;
void endVisit(Continue const& _node) override;
void endVisit(IndexRangeAccess const& _node) override;
void endVisit(Return const& _node) override;
bool visit(TryCatchClause const&) override;
void endVisit(TryCatchClause const&) override;
bool visit(TryStatement const& _node) override;
void pushInlineFrame(CallableDeclaration const& _callable) override;
void popInlineFrame(CallableDeclaration const& _callable) override;
void visitAssert(FunctionCall const& _funCall);
void visitAddMulMod(FunctionCall const& _funCall) override;
void internalFunctionCall(FunctionCall const& _funCall);
void externalFunctionCall(FunctionCall const& _funCall);
void externalFunctionCallToTrustedCode(FunctionCall const& _funCall);
void unknownFunctionCall(FunctionCall const& _funCall);
void makeArrayPopVerificationTarget(FunctionCall const& _arrayPop) override;
void makeOutOfBoundsVerificationTarget(IndexAccess const& _access) override;
/// Creates underflow/overflow verification targets.
std::pair<smtutil::Expression, smtutil::Expression> arithmeticOperation(
Token _op,
smtutil::Expression const& _left,
smtutil::Expression const& _right,
Type const* _commonType,
Expression const& _expression
) override;
//@}
/// Helpers.
//@{
void resetSourceAnalysis();
void resetContractAnalysis();
void eraseKnowledge();
void clearIndices(ContractDefinition const* _contract, FunctionDefinition const* _function = nullptr) override;
void setCurrentBlock(Predicate const& _block);
std::set<unsigned> transactionVerificationTargetsIds(ASTNode const* _txRoot);
//@}
/// Sort helpers.
//@{
smtutil::SortPointer sort(FunctionDefinition const& _function);
smtutil::SortPointer sort(ASTNode const* _block);
//@}
/// Predicate helpers.
//@{
/// @returns a new block of given _sort and _name.
Predicate const* createSymbolicBlock(smtutil::SortPointer _sort, std::string const& _name, PredicateType _predType, ASTNode const* _node = nullptr, ContractDefinition const* _contractContext = nullptr);
/// Creates summary predicates for all functions of all contracts
/// in a given _source.
void defineInterfacesAndSummaries(SourceUnit const& _source);
/// Creates a CHC system that, for a given contract,
/// - initializes its state variables (as 0 or given value, if any).
/// - "calls" the explicit constructor function of the contract, if any.
void defineContractInitializer(ContractDefinition const& _contract, ContractDefinition const& _contractContext);
/// Interface predicate over current variables.
smtutil::Expression interface();
smtutil::Expression interface(ContractDefinition const& _contract);
/// Error predicate over current variables.
smtutil::Expression error();
smtutil::Expression error(unsigned _idx);
/// Creates a block for the given _node.
Predicate const* createBlock(ASTNode const* _node, PredicateType _predType, std::string const& _prefix = "");
/// Creates a call block for the given function _function from contract _contract.
/// The contract is needed here because of inheritance.
/// There are different types of summaries, where the most common is FunctionSummary,
/// but other summaries are also used for internal and external function calls.
Predicate const* createSummaryBlock(
FunctionDefinition const& _function,
ContractDefinition const& _contract,
PredicateType _type = PredicateType::FunctionSummary
);
/// @returns a block related to @a _contract's constructor.
Predicate const* createConstructorBlock(ContractDefinition const& _contract, std::string const& _prefix);
/// Creates a new error block to be used by an assertion.
/// Also registers the predicate.
void createErrorBlock();
void connectBlocks(smtutil::Expression const& _from, smtutil::Expression const& _to, smtutil::Expression const& _constraints = smtutil::Expression(true));
/// @returns The initial constraints that set up the beginning of a function.
smtutil::Expression initialConstraints(ContractDefinition const& _contract, FunctionDefinition const* _function = nullptr);
/// @returns the symbolic values of the state variables at the beginning
/// of the current transaction.
std::vector<smtutil::Expression> initialStateVariables();
std::vector<smtutil::Expression> stateVariablesAtIndex(unsigned _index);
std::vector<smtutil::Expression> stateVariablesAtIndex(unsigned _index, ContractDefinition const& _contract);
/// @returns the current symbolic values of the current state variables.
std::vector<smtutil::Expression> currentStateVariables();
std::vector<smtutil::Expression> currentStateVariables(ContractDefinition const& _contract);
/// @returns the predicate name for a given node.
std::string predicateName(ASTNode const* _node, ContractDefinition const* _contract = nullptr);
/// @returns a predicate application after checking the predicate's type.
smtutil::Expression predicate(Predicate const& _block);
/// @returns the summary predicate for the called function.
smtutil::Expression predicate(FunctionCall const& _funCall);
/// @returns a predicate that defines a contract initializer for _contract in the context of _contractContext.
smtutil::Expression initializer(ContractDefinition const& _contract, ContractDefinition const& _contractContext);
/// @returns a predicate that defines a constructor summary.
smtutil::Expression summary(ContractDefinition const& _contract);
/// @returns a predicate that defines a function summary.
smtutil::Expression summary(FunctionDefinition const& _function);
smtutil::Expression summary(FunctionDefinition const& _function, ContractDefinition const& _contract);
//@}
/// Solver related.
//@{
/// Adds Horn rule to the solver.
void addRule(smtutil::Expression const& _rule, std::string const& _ruleName);
/// @returns <true, empty> if query is unsatisfiable (safe).
/// @returns <false, model> otherwise.
std::pair<smtutil::CheckResult, smtutil::CHCSolverInterface::CexGraph> query(smtutil::Expression const& _query, langutil::SourceLocation const& _location);
void verificationTargetEncountered(ASTNode const* const _errorNode, VerificationTargetType _type, smtutil::Expression const& _errorCondition);
void checkVerificationTargets();
// Forward declaration. Definition is below.
struct CHCVerificationTarget;
void checkAssertTarget(ASTNode const* _scope, CHCVerificationTarget const& _target);
void checkAndReportTarget(
CHCVerificationTarget const& _target,
langutil::ErrorId _errorReporterId,
std::string _satMsg,
std::string _unknownMsg = ""
);
std::optional<std::string> generateCounterexample(smtutil::CHCSolverInterface::CexGraph const& _graph, std::string const& _root);
/// @returns a call graph for function summaries in the counterexample graph.
/// The returned map also contains a key _root, whose value are the
/// summaries called by _root.
std::map<unsigned, std::vector<unsigned>> summaryCalls(
smtutil::CHCSolverInterface::CexGraph const& _graph,
unsigned _root
);
/// @returns a set of pairs _var = _value separated by _separator.
template <typename T>
std::string formatVariableModel(std::vector<T> const& _variables, std::vector<std::optional<std::string>> const& _values, std::string const& _separator) const
{
solAssert(_variables.size() == _values.size(), "");
std::vector<std::string> assignments;
for (unsigned i = 0; i < _values.size(); ++i)
{
auto var = _variables.at(i);
if (var && _values.at(i))
assignments.emplace_back(var->name() + " = " + *_values.at(i));
}
return boost::algorithm::join(assignments, _separator);
}
/// @returns a DAG in the dot format.
/// Used for debugging purposes.
std::string cex2dot(smtutil::CHCSolverInterface::CexGraph const& _graph);
//@}
/// Misc.
//@{
/// @returns a prefix to be used in a new unique block name
/// and increases the block counter.
std::string uniquePrefix();
/// @returns a suffix to be used by contract related predicates.
std::string contractSuffix(ContractDefinition const& _contract);
/// @returns a new unique error id associated with _expr and stores
/// it into m_errorIds.
unsigned newErrorId();
smt::SymbolicIntVariable& errorFlag();
//@}
/// Predicates.
//@{
/// Artificial Interface predicate.
/// Single entry block for all functions.
std::map<ContractDefinition const*, Predicate const*> m_interfaces;
/// Nondeterministic interfaces.
/// These are used when the analyzed contract makes external calls to unknown code,
/// which means that the analyzed contract can potentially be called
/// nondeterministically.
std::map<ContractDefinition const*, Predicate const*> m_nondetInterfaces;
std::map<ContractDefinition const*, Predicate const*> m_constructorSummaries;
std::map<ContractDefinition const*, std::map<ContractDefinition const*, Predicate const*>> m_contractInitializers;
/// Artificial Error predicate.
/// Single error block for all assertions.
Predicate const* m_errorPredicate = nullptr;
/// Function predicates.
std::map<ContractDefinition const*, std::map<FunctionDefinition const*, Predicate const*>> m_summaries;
//@}
/// Variables.
//@{
/// State variables.
/// Used to create all predicates.
std::vector<VariableDeclaration const*> m_stateVariables;
//@}
/// Verification targets.
//@{
struct CHCVerificationTarget: VerificationTarget
{
unsigned const errorId;
ASTNode const* const errorNode;
};
/// Query placeholder stores information necessary to create the final query edge in the CHC system.
/// It is combined with the unique error id (and error type) to create a complete Verification Target.
struct CHCQueryPlaceholder
{
smtutil::Expression const constraints;
smtutil::Expression const errorExpression;
smtutil::Expression const fromPredicate;
};
/// Query placeholders for constructors, if the key has type ContractDefinition*,
/// or external functions, if the key has type FunctionDefinition*.
/// A placeholder is created for each possible context of a function (e.g. multiple contracts in contract inheritance hierarchy).
std::map<ASTNode const*, std::vector<CHCQueryPlaceholder>, smt::EncodingContext::IdCompare> m_queryPlaceholders;
/// Records verification conditions IDs per function encountered during an analysis of that function.
/// The key is the ASTNode of the function where the verification condition has been encountered,
/// or the ASTNode of the contract if the verification condition happens inside an implicit constructor.
std::map<ASTNode const*, std::vector<unsigned>, smt::EncodingContext::IdCompare> m_functionTargetIds;
/// Helper mapping unique IDs to actual verification targets.
std::map<unsigned, CHCVerificationTarget> m_verificationTargets;
/// Targets proven safe.
std::map<ASTNode const*, std::set<VerificationTargetType>> m_safeTargets;
/// Targets proven unsafe.
std::map<ASTNode const*, std::set<VerificationTargetType>> m_unsafeTargets;
//@}
/// Control-flow.
//@{
FunctionDefinition const* m_currentFunction = nullptr;
std::map<ASTNode const*, std::set<ASTNode const*, smt::EncodingContext::IdCompare>, smt::EncodingContext::IdCompare> m_callGraph;
/// The current block.
smtutil::Expression m_currentBlock = smtutil::Expression(true);
/// Counter to generate unique block names.
unsigned m_blockCounter = 0;
/// Whether a function call was seen in the current scope.
bool m_unknownFunctionCallSeen = false;
/// Block where a loop break should go to.
Predicate const* m_breakDest = nullptr;
/// Block where a loop continue should go to.
Predicate const* m_continueDest = nullptr;
/// Block where an error condition should go to.
/// This can be:
/// 1) Constructor initializer summary, if error happens while evaluating initial values of state variables.
/// 2) Constructor summary, if error happens while evaluating base constructor arguments.
/// 3) Function summary, if error happens inside a function.
Predicate const* m_errorDest = nullptr;
/// Represents the stack of destinations where a `return` should go.
/// This is different from `m_errorDest` above:
/// - Constructor initializers and constructor summaries will never be `return` targets because they are artificial.
/// - Modifiers also have their own `return` target blocks, whereas they do not have their own error destination.
std::vector<Predicate const*> m_returnDests;
//@}
/// CHC solver.
std::unique_ptr<smtutil::CHCSolverInterface> m_interface;
/// ErrorReporter that comes from CompilerStack.
langutil::ErrorReporter& m_outerErrorReporter;
/// SMT solvers that are chosen at runtime.
smtutil::SMTSolverChoice m_enabledSolvers;
ModelCheckerSettings const& m_settings;
};
}