[clang] [analyzer] Add alpha.cplusplus.BoundsInformation checker (PR #112784)

[Artem Dergachev via cfe-commits]

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@@ -0,0 +1,199 @@
+//== BoundsInformationChecker.cpp - bounds information checker --*- 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
+//
+//===----------------------------------------------------------------------===//
+//
+// This defines BoundsInformationChecker, a path-sensitive checker that
+// checks that the buffer and count arguments are within the bounds of
+// the source buffer.
+//
+//===----------------------------------------------------------------------===//
+
+#include "clang/StaticAnalyzer/Checkers/BuiltinCheckerRegistration.h"
+#include "clang/StaticAnalyzer/Core/BugReporter/BugType.h"
+#include "clang/StaticAnalyzer/Core/BugReporter/CommonBugCategories.h"
+#include "clang/StaticAnalyzer/Core/Checker.h"
+#include "clang/StaticAnalyzer/Core/CheckerManager.h"
+#include "clang/StaticAnalyzer/Core/PathSensitive/CallDescription.h"
+#include "clang/StaticAnalyzer/Core/PathSensitive/CallEvent.h"
+#include "clang/StaticAnalyzer/Core/PathSensitive/CheckerContext.h"
+#include "clang/StaticAnalyzer/Core/PathSensitive/MemRegion.h"
+
+using namespace clang;
+using namespace ento;
+
+namespace {
+class BoundsInformationChecker : public Checker<check::PreCall> {
+  const BugType BT_DifferentMemRegion{
+      this, "std::span constructor arguments from different sources",
+      categories::SecurityError};
+  const BugType BT_NonConstantSizeArg{
+      this,
+      "std::span constructor for std::array has non-constant size argument",
+      categories::SecurityError};
+  const BugType BT_OutOfBounds{
+      this,
+      "std::span constructor for std::array uses out-of-bounds size argument",
+      categories::SecurityError};
+  void reportBug(ExplodedNode *N, const Expr *E, CheckerContext &C,
+                 const BugType &BT, StringRef Msg) const;
+
+public:
+  void checkPreCall(const CallEvent &Call, CheckerContext &C) const;
+};
+} // end anonymous namespace
+
+void BoundsInformationChecker::reportBug(ExplodedNode *N, const Expr *E,
+                                         CheckerContext &C, const BugType &BT,
+                                         StringRef Msg) const {
+  // Generate a report for this bug.
+  auto R = std::make_unique<PathSensitiveBugReport>(BT, Msg, N);
+  if (auto *CE = dyn_cast<CXXConstructExpr>(E)) {
+    bugreporter::trackExpressionValue(N, CE->getArg(0), *R);
+    bugreporter::trackExpressionValue(N, CE->getArg(1), *R);
+  }
+  C.emitReport(std::move(R));
+}
+
+static const MemRegion *GetRegionOrigin(SVal SV) {
+  const SymExpr *Sym = SV.getAsSymbol(/*IncludeBaseRegions =*/true);
+  return Sym ? Sym->getOriginRegion() : nullptr;
+}
+
+static const ValueDecl *GetExpressionOrigin(const Stmt *STMT) {
+  if (const DeclRefExpr *DRE = dyn_cast<DeclRefExpr>(STMT)) {
+    if (const VarDecl *VD = dyn_cast<VarDecl>(DRE->getDecl()))
+      return VD;
+  } else if (const CXXMemberCallExpr *MCE = dyn_cast<CXXMemberCallExpr>(STMT)) {
+    if (const DeclRefExpr *DRE = dyn_cast<DeclRefExpr>(
+            MCE->getImplicitObjectArgument()->IgnoreParenCasts())) {
+      if (const VarDecl *VD = dyn_cast<VarDecl>(DRE->getDecl()))
+        return VD;
+    } else if (const MemberExpr *ME = dyn_cast<MemberExpr>(
+                   MCE->getImplicitObjectArgument()->IgnoreParenCasts())) {
+      if (const FieldDecl *FD = dyn_cast<FieldDecl>(ME->getMemberDecl()))
+        return FD;
+    }
+  } else if (const CXXOperatorCallExpr *OCE =
+                 dyn_cast<CXXOperatorCallExpr>(STMT)) {
+    if (OCE->getNumArgs() >= 1) {
+      if (const DeclRefExpr *DRE = dyn_cast<DeclRefExpr>(OCE->getArg(0))) {
+        if (const VarDecl *VD = dyn_cast<VarDecl>(DRE->getDecl()))
+          return VD;
+      }
+    }
+  } else if (const UnaryOperator *UnaryOp = dyn_cast<UnaryOperator>(STMT)) {
+    if (const ArraySubscriptExpr *ASExpr =
+            dyn_cast<ArraySubscriptExpr>(UnaryOp->getSubExpr())) {
+      if (const DeclRefExpr *DRE =
+              dyn_cast<DeclRefExpr>(ASExpr->getBase()->IgnoreParenCasts())) {
+        if (const VarDecl *VD = dyn_cast<VarDecl>(DRE->getDecl()))
+          return VD;
+      }
+    }
+  } else if (const UnaryExprOrTypeTraitExpr *UTExpr =
+                 dyn_cast<UnaryExprOrTypeTraitExpr>(STMT)) {
+    if (const DeclRefExpr *DRE = dyn_cast<DeclRefExpr>(
+            UTExpr->getArgumentExpr()->IgnoreParenCasts())) {
+      if (const VarDecl *VD = dyn_cast<VarDecl>(DRE->getDecl()))
+        return VD;
+    }
+  }
+  return nullptr;
+}
+
+static const ValueDecl *GetConjuredSymbolOrigin(SVal SV) {
+  const SymExpr *Sym = SV.getAsSymbol(/*IncludeBaseRegions =*/true);
+  if (const SymbolConjured *SCArg = dyn_cast_or_null<SymbolConjured>(Sym)) {
+    if (const Stmt *STMTArg = SCArg->getStmt())
+      return GetExpressionOrigin(STMTArg);
+  }
+  return nullptr;
+}
+
+void BoundsInformationChecker::checkPreCall(const CallEvent &Call,
+                                            CheckerContext &C) const {
+  // Return early if not std::span<IT>(IT, size_t) constructor.
+  // a. Check if this is a ctor for std::span.
+  CallDescription CD({CDM::CXXMethod, {"std", "span", "span"}});
+  if (!CD.matches(Call))
+    return;
+  // b. Check if std::span ctor has two arguments.
+  if (Call.getNumArgs() != 2)
+    return;
+  // c. Check if second std::span ctor argument is of type size_t.
+  if (Call.getArgExpr(1)->getType().getCanonicalType() !=
+      C.getASTContext().getSizeType())
+    return;
+
+  SVal PointerArg = Call.getArgSVal(0);
+  SVal SizeArg = Call.getArgSVal(1);
+
+  // If buffer and length params are not from the same "source", then report a
+  // bug.
+  const MemRegion *MRArg0 = GetRegionOrigin(PointerArg);
+  const MemRegion *MRArg1 = GetRegionOrigin(SizeArg);
+  if (MRArg0 && MRArg1 && MRArg0->getBaseRegion() != MRArg1->getBaseRegion()) {
+    // FIXME: Add more logic to filter out valid cases.
+    if (ExplodedNode *N = C.generateNonFatalErrorNode(C.getState())) {
+      reportBug(
+          N, Call.getOriginExpr(), C, BT_DifferentMemRegion,
+          "Constructor args for std::span are from different memory regions");
----------------
haoNoQ wrote:

I don't think you have any "positive" tests for this warning yet. It's a good idea to have some!

Wording: "memory regions" is our local terminology. Users won't necessarily understand what it means. I think we should say "from different sources" or something like that. Though, of course, this warning will probably change quite a bit as we figure out the specific cases in which we want to emit it. (It may be a good idea to have different warnings for different cases.)

https://github.com/llvm/llvm-project/pull/112784