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llvm-project/clang/lib/StaticAnalyzer/Checkers/ExprInspectionChecker.cpp
Balazs Benics f8643a9b31 [analyzer] Prefer wrapping SymbolicRegions by ElementRegions 
It turns out that in certain cases `SymbolRegions` are wrapped by
`ElementRegions`; in others, it's not. This discrepancy can cause the
analyzer not to recognize if the two regions are actually referring to
the same entity, which then can lead to unreachable paths discovered.

Consider this example:

```lang=C++
struct Node { int* ptr; };
void with_structs(Node* n1) {
  Node c = *n1; // copy
  Node* n2 = &c;
  clang_analyzer_dump(*n1); // lazy...
  clang_analyzer_dump(*n2); // lazy...
  clang_analyzer_dump(n1->ptr); // rval(n1->ptr): reg_$2<int * SymRegion{reg_$0<struct Node * n1>}.ptr>
  clang_analyzer_dump(n2->ptr); // rval(n2->ptr): reg_$1<int * Element{SymRegion{reg_$0<struct Node * n1>},0 S64b,struct Node}.ptr>
  clang_analyzer_eval(n1->ptr != n2->ptr); // UNKNOWN, bad!
  (void)(*n1);
  (void)(*n2);
}
```

The copy of `n1` will insert a new binding to the store; but for doing
that it actually must create a `TypedValueRegion` which it could pass to
the `LazyCompoundVal`. Since the memregion in question is a
`SymbolicRegion` - which is untyped, it needs to first wrap it into an
`ElementRegion` basically implementing this untyped -> typed conversion
for the sake of passing it to the `LazyCompoundVal`.
So, this is why we have `Element{SymRegion{.}, 0,struct Node}` for `n1`.

The problem appears if the analyzer evaluates a read from the expression
`n1->ptr`. The same logic won't apply for `SymbolRegionValues`, since
they accept raw `SubRegions`, hence the `SymbolicRegion` won't be
wrapped into an `ElementRegion` in that case.

Later when we arrive at the equality comparison, we cannot prove that
they are equal.

For more details check the corresponding thread on discourse:
https://discourse.llvm.org/t/are-symbolicregions-really-untyped/64406

---

In this patch, I'm eagerly wrapping each `SymbolicRegion` by an
`ElementRegion`; basically canonicalizing to this form.
It seems reasonable to do so since any object can be thought of as a single
array of that object; so this should not make much of a difference.

The tests also underpin this assumption, as only a few were broken by
this change; and actually fixed a FIXME along the way.

About the second example, which does the same copy operation - but on
the heap - it will be fixed by the next patch.

Reviewed By: martong

Differential Revision: https://reviews.llvm.org/D132142
2022-09-13 08:58:46 +02:00

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//==- ExprInspectionChecker.cpp - Used for regression tests ------*- C++ -*-==//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
#include "clang/Analysis/IssueHash.h"
#include "clang/StaticAnalyzer/Checkers/BuiltinCheckerRegistration.h"
#include "clang/StaticAnalyzer/Checkers/SValExplainer.h"
#include "clang/StaticAnalyzer/Checkers/Taint.h"
#include "clang/StaticAnalyzer/Core/BugReporter/BugType.h"
#include "clang/StaticAnalyzer/Core/Checker.h"
#include "clang/StaticAnalyzer/Core/PathSensitive/CallEvent.h"
#include "clang/StaticAnalyzer/Core/PathSensitive/CheckerContext.h"
#include "clang/StaticAnalyzer/Core/PathSensitive/DynamicExtent.h"
#include "llvm/ADT/StringSwitch.h"
#include "llvm/Support/ScopedPrinter.h"
using namespace clang;
using namespace ento;
namespace {
class ExprInspectionChecker
: public Checker<eval::Call, check::DeadSymbols, check::EndAnalysis> {
mutable std::unique_ptr<BugType> BT;
// These stats are per-analysis, not per-branch, hence they shouldn't
// stay inside the program state.
struct ReachedStat {
ExplodedNode *ExampleNode;
unsigned NumTimesReached;
};
mutable llvm::DenseMap<const CallExpr *, ReachedStat> ReachedStats;
void analyzerEval(const CallExpr *CE, CheckerContext &C) const;
void analyzerCheckInlined(const CallExpr *CE, CheckerContext &C) const;
void analyzerWarnIfReached(const CallExpr *CE, CheckerContext &C) const;
void analyzerNumTimesReached(const CallExpr *CE, CheckerContext &C) const;
void analyzerCrash(const CallExpr *CE, CheckerContext &C) const;
void analyzerWarnOnDeadSymbol(const CallExpr *CE, CheckerContext &C) const;
void analyzerValue(const CallExpr *CE, CheckerContext &C) const;
void analyzerDumpSValType(const CallExpr *CE, CheckerContext &C) const;
void analyzerDump(const CallExpr *CE, CheckerContext &C) const;
void analyzerExplain(const CallExpr *CE, CheckerContext &C) const;
void analyzerPrintState(const CallExpr *CE, CheckerContext &C) const;
void analyzerGetExtent(const CallExpr *CE, CheckerContext &C) const;
void analyzerDumpExtent(const CallExpr *CE, CheckerContext &C) const;
void analyzerDumpElementCount(const CallExpr *CE, CheckerContext &C) const;
void analyzerHashDump(const CallExpr *CE, CheckerContext &C) const;
void analyzerDenote(const CallExpr *CE, CheckerContext &C) const;
void analyzerExpress(const CallExpr *CE, CheckerContext &C) const;
void analyzerIsTainted(const CallExpr *CE, CheckerContext &C) const;
typedef void (ExprInspectionChecker::*FnCheck)(const CallExpr *,
CheckerContext &C) const;
// Optional parameter `ExprVal` for expression value to be marked interesting.
ExplodedNode *reportBug(llvm::StringRef Msg, CheckerContext &C,
Optional<SVal> ExprVal = None) const;
ExplodedNode *reportBug(llvm::StringRef Msg, BugReporter &BR, ExplodedNode *N,
Optional<SVal> ExprVal = None) const;
template <typename T> void printAndReport(CheckerContext &C, T What) const;
const Expr *getArgExpr(const CallExpr *CE, CheckerContext &C) const;
const MemRegion *getArgRegion(const CallExpr *CE, CheckerContext &C) const;
public:
bool evalCall(const CallEvent &Call, CheckerContext &C) const;
void checkDeadSymbols(SymbolReaper &SymReaper, CheckerContext &C) const;
void checkEndAnalysis(ExplodedGraph &G, BugReporter &BR,
ExprEngine &Eng) const;
};
} // namespace
REGISTER_SET_WITH_PROGRAMSTATE(MarkedSymbols, SymbolRef)
REGISTER_MAP_WITH_PROGRAMSTATE(DenotedSymbols, SymbolRef, const StringLiteral *)
bool ExprInspectionChecker::evalCall(const CallEvent &Call,
CheckerContext &C) const {
const auto *CE = dyn_cast_or_null<CallExpr>(Call.getOriginExpr());
if (!CE)
return false;
// These checks should have no effect on the surrounding environment
// (globals should not be invalidated, etc), hence the use of evalCall.
FnCheck Handler =
llvm::StringSwitch<FnCheck>(C.getCalleeName(CE))
.Case("clang_analyzer_eval", &ExprInspectionChecker::analyzerEval)
.Case("clang_analyzer_checkInlined",
&ExprInspectionChecker::analyzerCheckInlined)
.Case("clang_analyzer_crash", &ExprInspectionChecker::analyzerCrash)
.Case("clang_analyzer_warnIfReached",
&ExprInspectionChecker::analyzerWarnIfReached)
.Case("clang_analyzer_warnOnDeadSymbol",
&ExprInspectionChecker::analyzerWarnOnDeadSymbol)
.StartsWith("clang_analyzer_explain",
&ExprInspectionChecker::analyzerExplain)
.Case("clang_analyzer_dumpExtent",
&ExprInspectionChecker::analyzerDumpExtent)
.Case("clang_analyzer_dumpElementCount",
&ExprInspectionChecker::analyzerDumpElementCount)
.Case("clang_analyzer_value", &ExprInspectionChecker::analyzerValue)
.StartsWith("clang_analyzer_dumpSvalType",
&ExprInspectionChecker::analyzerDumpSValType)
.StartsWith("clang_analyzer_dump",
&ExprInspectionChecker::analyzerDump)
.Case("clang_analyzer_getExtent",
&ExprInspectionChecker::analyzerGetExtent)
.Case("clang_analyzer_printState",
&ExprInspectionChecker::analyzerPrintState)
.Case("clang_analyzer_numTimesReached",
&ExprInspectionChecker::analyzerNumTimesReached)
.Case("clang_analyzer_hashDump",
&ExprInspectionChecker::analyzerHashDump)
.Case("clang_analyzer_denote", &ExprInspectionChecker::analyzerDenote)
.Case("clang_analyzer_express",
&ExprInspectionChecker::analyzerExpress)
.StartsWith("clang_analyzer_isTainted",
&ExprInspectionChecker::analyzerIsTainted)
.Default(nullptr);
if (!Handler)
return false;
(this->*Handler)(CE, C);
return true;
}
static const char *getArgumentValueString(const CallExpr *CE,
CheckerContext &C) {
if (CE->getNumArgs() == 0)
return "Missing assertion argument";
ExplodedNode *N = C.getPredecessor();
const LocationContext *LC = N->getLocationContext();
ProgramStateRef State = N->getState();
const Expr *Assertion = CE->getArg(0);
SVal AssertionVal = State->getSVal(Assertion, LC);
if (AssertionVal.isUndef())
return "UNDEFINED";
ProgramStateRef StTrue, StFalse;
std::tie(StTrue, StFalse) =
State->assume(AssertionVal.castAs<DefinedOrUnknownSVal>());
if (StTrue) {
if (StFalse)
return "UNKNOWN";
else
return "TRUE";
} else {
if (StFalse)
return "FALSE";
else
llvm_unreachable("Invalid constraint; neither true or false.");
}
}
ExplodedNode *ExprInspectionChecker::reportBug(llvm::StringRef Msg,
CheckerContext &C,
Optional<SVal> ExprVal) const {
ExplodedNode *N = C.generateNonFatalErrorNode();
reportBug(Msg, C.getBugReporter(), N, ExprVal);
return N;
}
ExplodedNode *ExprInspectionChecker::reportBug(llvm::StringRef Msg,
BugReporter &BR, ExplodedNode *N,
Optional<SVal> ExprVal) const {
if (!N)
return nullptr;
if (!BT)
BT.reset(new BugType(this, "Checking analyzer assumptions", "debug"));
auto R = std::make_unique<PathSensitiveBugReport>(*BT, Msg, N);
if (ExprVal) {
R->markInteresting(*ExprVal);
}
BR.emitReport(std::move(R));
return N;
}
const Expr *ExprInspectionChecker::getArgExpr(const CallExpr *CE,
CheckerContext &C) const {
if (CE->getNumArgs() == 0) {
reportBug("Missing argument", C);
return nullptr;
}
return CE->getArg(0);
}
const MemRegion *ExprInspectionChecker::getArgRegion(const CallExpr *CE,
CheckerContext &C) const {
const Expr *Arg = getArgExpr(CE, C);
if (!Arg)
return nullptr;
const MemRegion *MR = C.getSVal(Arg).getAsRegion();
if (!MR) {
reportBug("Cannot obtain the region", C);
return nullptr;
}
return MR;
}
void ExprInspectionChecker::analyzerEval(const CallExpr *CE,
CheckerContext &C) const {
const LocationContext *LC = C.getPredecessor()->getLocationContext();
// A specific instantiation of an inlined function may have more constrained
// values than can generally be assumed. Skip the check.
if (LC->getStackFrame()->getParent() != nullptr)
return;
reportBug(getArgumentValueString(CE, C), C);
}
void ExprInspectionChecker::analyzerWarnIfReached(const CallExpr *CE,
CheckerContext &C) const {
reportBug("REACHABLE", C);
}
void ExprInspectionChecker::analyzerNumTimesReached(const CallExpr *CE,
CheckerContext &C) const {
++ReachedStats[CE].NumTimesReached;
if (!ReachedStats[CE].ExampleNode) {
// Later, in checkEndAnalysis, we'd throw a report against it.
ReachedStats[CE].ExampleNode = C.generateNonFatalErrorNode();
}
}
void ExprInspectionChecker::analyzerCheckInlined(const CallExpr *CE,
CheckerContext &C) const {
const LocationContext *LC = C.getPredecessor()->getLocationContext();
// An inlined function could conceivably also be analyzed as a top-level
// function. We ignore this case and only emit a message (TRUE or FALSE)
// when we are analyzing it as an inlined function. This means that
// clang_analyzer_checkInlined(true) should always print TRUE, but
// clang_analyzer_checkInlined(false) should never actually print anything.
if (LC->getStackFrame()->getParent() == nullptr)
return;
reportBug(getArgumentValueString(CE, C), C);
}
void ExprInspectionChecker::analyzerExplain(const CallExpr *CE,
CheckerContext &C) const {
const Expr *Arg = getArgExpr(CE, C);
if (!Arg)
return;
SVal V = C.getSVal(Arg);
SValExplainer Ex(C.getASTContext());
reportBug(Ex.Visit(V), C);
}
static void printHelper(llvm::raw_svector_ostream &Out, CheckerContext &C,
const llvm::APSInt &I) {
Out << I.getBitWidth() << (I.isUnsigned() ? "u:" : "s:");
Out << I;
}
static void printHelper(llvm::raw_svector_ostream &Out, CheckerContext &C,
SymbolRef Sym) {
C.getConstraintManager().printValue(Out, C.getState(), Sym);
}
static void printHelper(llvm::raw_svector_ostream &Out, CheckerContext &C,
SVal V) {
Out << V;
}
template <typename T>
void ExprInspectionChecker::printAndReport(CheckerContext &C, T What) const {
llvm::SmallString<64> Str;
llvm::raw_svector_ostream OS(Str);
printHelper(OS, C, What);
reportBug(OS.str(), C);
}
void ExprInspectionChecker::analyzerValue(const CallExpr *CE,
CheckerContext &C) const {
const Expr *Arg = getArgExpr(CE, C);
if (!Arg)
return;
SVal V = C.getSVal(Arg);
if (const SymbolRef Sym = V.getAsSymbol())
printAndReport(C, Sym);
else if (const llvm::APSInt *I = V.getAsInteger())
printAndReport(C, *I);
else
reportBug("n/a", C);
}
void ExprInspectionChecker::analyzerDumpSValType(const CallExpr *CE,
CheckerContext &C) const {
const Expr *Arg = getArgExpr(CE, C);
if (!Arg)
return;
QualType Ty = C.getSVal(Arg).getType(C.getASTContext());
reportBug(Ty.getAsString(), C);
}
void ExprInspectionChecker::analyzerDump(const CallExpr *CE,
CheckerContext &C) const {
const Expr *Arg = getArgExpr(CE, C);
if (!Arg)
return;
SVal V = C.getSVal(Arg);
printAndReport(C, V);
}
void ExprInspectionChecker::analyzerGetExtent(const CallExpr *CE,
CheckerContext &C) const {
const MemRegion *MR = getArgRegion(CE, C);
if (!MR)
return;
ProgramStateRef State = C.getState();
DefinedOrUnknownSVal Size = getDynamicExtent(State, MR, C.getSValBuilder());
State = State->BindExpr(CE, C.getLocationContext(), Size);
C.addTransition(State);
}
void ExprInspectionChecker::analyzerDumpExtent(const CallExpr *CE,
CheckerContext &C) const {
const MemRegion *MR = getArgRegion(CE, C);
if (!MR)
return;
DefinedOrUnknownSVal Size =
getDynamicExtent(C.getState(), MR, C.getSValBuilder());
printAndReport(C, Size);
}
void ExprInspectionChecker::analyzerDumpElementCount(const CallExpr *CE,
CheckerContext &C) const {
const MemRegion *MR = getArgRegion(CE, C);
if (!MR)
return;
QualType ElementTy;
if (const auto *TVR = MR->getAs<TypedValueRegion>()) {
ElementTy = TVR->getValueType();
} else {
ElementTy = MR->castAs<SymbolicRegion>()->getPointeeStaticType();
}
assert(!ElementTy->isPointerType());
DefinedOrUnknownSVal ElementCount =
getDynamicElementCount(C.getState(), MR, C.getSValBuilder(), ElementTy);
printAndReport(C, ElementCount);
}
void ExprInspectionChecker::analyzerPrintState(const CallExpr *CE,
CheckerContext &C) const {
C.getState()->dump();
}
void ExprInspectionChecker::analyzerWarnOnDeadSymbol(const CallExpr *CE,
CheckerContext &C) const {
const Expr *Arg = getArgExpr(CE, C);
if (!Arg)
return;
SVal Val = C.getSVal(Arg);
SymbolRef Sym = Val.getAsSymbol();
if (!Sym)
return;
ProgramStateRef State = C.getState();
State = State->add<MarkedSymbols>(Sym);
C.addTransition(State);
}
void ExprInspectionChecker::checkDeadSymbols(SymbolReaper &SymReaper,
CheckerContext &C) const {
ProgramStateRef State = C.getState();
const MarkedSymbolsTy &Syms = State->get<MarkedSymbols>();
ExplodedNode *N = C.getPredecessor();
for (auto I = Syms.begin(), E = Syms.end(); I != E; ++I) {
SymbolRef Sym = *I;
if (!SymReaper.isDead(Sym))
continue;
// The non-fatal error node should be the same for all reports.
if (ExplodedNode *BugNode = reportBug("SYMBOL DEAD", C))
N = BugNode;
State = State->remove<MarkedSymbols>(Sym);
}
for (auto I : State->get<DenotedSymbols>()) {
SymbolRef Sym = I.first;
if (!SymReaper.isLive(Sym))
State = State->remove<DenotedSymbols>(Sym);
}
C.addTransition(State, N);
}
void ExprInspectionChecker::checkEndAnalysis(ExplodedGraph &G, BugReporter &BR,
ExprEngine &Eng) const {
for (auto Item : ReachedStats) {
unsigned NumTimesReached = Item.second.NumTimesReached;
ExplodedNode *N = Item.second.ExampleNode;
reportBug(llvm::to_string(NumTimesReached), BR, N);
}
ReachedStats.clear();
}
void ExprInspectionChecker::analyzerCrash(const CallExpr *CE,
CheckerContext &C) const {
LLVM_BUILTIN_TRAP;
}
void ExprInspectionChecker::analyzerHashDump(const CallExpr *CE,
CheckerContext &C) const {
const LangOptions &Opts = C.getLangOpts();
const SourceManager &SM = C.getSourceManager();
FullSourceLoc FL(CE->getArg(0)->getBeginLoc(), SM);
std::string HashContent =
getIssueString(FL, getCheckerName().getName(), "Category",
C.getLocationContext()->getDecl(), Opts);
reportBug(HashContent, C);
}
void ExprInspectionChecker::analyzerDenote(const CallExpr *CE,
CheckerContext &C) const {
if (CE->getNumArgs() < 2) {
reportBug("clang_analyzer_denote() requires a symbol and a string literal",
C);
return;
}
SymbolRef Sym = C.getSVal(CE->getArg(0)).getAsSymbol();
if (!Sym) {
reportBug("Not a symbol", C);
return;
}
const auto *E = dyn_cast<StringLiteral>(CE->getArg(1)->IgnoreParenCasts());
if (!E) {
reportBug("Not a string literal", C);
return;
}
ProgramStateRef State = C.getState();
C.addTransition(C.getState()->set<DenotedSymbols>(Sym, E));
}
namespace {
class SymbolExpressor
: public SymExprVisitor<SymbolExpressor, Optional<std::string>> {
ProgramStateRef State;
public:
SymbolExpressor(ProgramStateRef State) : State(State) {}
Optional<std::string> lookup(const SymExpr *S) {
if (const StringLiteral *const *SLPtr = State->get<DenotedSymbols>(S)) {
const StringLiteral *SL = *SLPtr;
return std::string(SL->getBytes());
}
return None;
}
Optional<std::string> VisitSymExpr(const SymExpr *S) { return lookup(S); }
Optional<std::string> VisitSymIntExpr(const SymIntExpr *S) {
if (Optional<std::string> Str = lookup(S))
return Str;
if (Optional<std::string> Str = Visit(S->getLHS()))
return (*Str + " " + BinaryOperator::getOpcodeStr(S->getOpcode()) + " " +
std::to_string(S->getRHS().getLimitedValue()) +
(S->getRHS().isUnsigned() ? "U" : ""))
.str();
return None;
}
Optional<std::string> VisitSymSymExpr(const SymSymExpr *S) {
if (Optional<std::string> Str = lookup(S))
return Str;
if (Optional<std::string> Str1 = Visit(S->getLHS()))
if (Optional<std::string> Str2 = Visit(S->getRHS()))
return (*Str1 + " " + BinaryOperator::getOpcodeStr(S->getOpcode()) +
" " + *Str2)
.str();
return None;
}
Optional<std::string> VisitUnarySymExpr(const UnarySymExpr *S) {
if (Optional<std::string> Str = lookup(S))
return Str;
if (Optional<std::string> Str = Visit(S->getOperand()))
return (UnaryOperator::getOpcodeStr(S->getOpcode()) + *Str).str();
return None;
}
Optional<std::string> VisitSymbolCast(const SymbolCast *S) {
if (Optional<std::string> Str = lookup(S))
return Str;
if (Optional<std::string> Str = Visit(S->getOperand()))
return (Twine("(") + S->getType().getAsString() + ")" + *Str).str();
return None;
}
};
} // namespace
void ExprInspectionChecker::analyzerExpress(const CallExpr *CE,
CheckerContext &C) const {
const Expr *Arg = getArgExpr(CE, C);
if (!Arg)
return;
SVal ArgVal = C.getSVal(CE->getArg(0));
SymbolRef Sym = ArgVal.getAsSymbol();
if (!Sym) {
reportBug("Not a symbol", C);
return;
}
SymbolExpressor V(C.getState());
auto Str = V.Visit(Sym);
if (!Str) {
reportBug("Unable to express", C);
return;
}
reportBug(*Str, C, ArgVal);
}
void ExprInspectionChecker::analyzerIsTainted(const CallExpr *CE,
CheckerContext &C) const {
if (CE->getNumArgs() != 1) {
reportBug("clang_analyzer_isTainted() requires exactly one argument", C);
return;
}
const bool IsTainted =
taint::isTainted(C.getState(), CE->getArg(0), C.getLocationContext());
reportBug(IsTainted ? "YES" : "NO", C);
}
void ento::registerExprInspectionChecker(CheckerManager &Mgr) {
Mgr.registerChecker<ExprInspectionChecker>();
}
bool ento::shouldRegisterExprInspectionChecker(const CheckerManager &mgr) {
return true;
}
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