[analyzer] Split TaintPropagation checker into reporting and modeling checkers (#98157)

Taint propagation is a a generic modeling feature of the Clang Static
Analyzer which many other checkers depend on. Therefore
GenericTaintChecker is split into a TaintPropagation modeling checker
and a GenericTaint reporting checker.

Author: dkrupp

clang/docs/analyzer/checkers.rst

@@ -1003,17 +1003,14 @@ array new C++ operator is tainted (potentially attacker controlled).
 If an attacker can inject a large value as the size parameter, memory exhaustion
 denial of service attack can be carried out.
 
-The ``alpha.security.taint.TaintPropagation`` checker also needs to be enabled for
-this checker to give warnings.
-
 The analyzer emits warning only if it cannot prove that the size parameter is
 within reasonable bounds (``<= SIZE_MAX/4``). This functionality partially
 covers the SEI Cert coding standard rule `INT04-C
 <https://wiki.sei.cmu.edu/confluence/display/c/INT04-C.+Enforce+limits+on+integer+values+originating+from+tainted+sources>`_.
 
 You can silence this warning either by bound checking the ``size`` parameter, or
 by explicitly marking the ``size`` parameter as sanitized. See the
-:ref:`alpha-security-taint-TaintPropagation` checker for more details.
+:ref:`alpha-security-taint-GenericTaint` checker for an example.
 
 .. code-block:: c
 
@@ -3011,10 +3008,10 @@ alpha.security.taint
 Checkers implementing
 `taint analysis <https://en.wikipedia.org/wiki/Taint_checking>`_.
 
-.. _alpha-security-taint-TaintPropagation:
+.. _alpha-security-taint-GenericTaint:
 
-alpha.security.taint.TaintPropagation (C, C++)
-""""""""""""""""""""""""""""""""""""""""""""""
+alpha.security.taint.GenericTaint (C, C++)
+""""""""""""""""""""""""""""""""""""""""""
 
 Taint analysis identifies potential security vulnerabilities where the
 attacker can inject malicious data to the program to execute an attack

clang/docs/analyzer/user-docs/TaintAnalysisConfiguration.rst

@@ -2,10 +2,13 @@
 Taint Analysis Configuration
 ============================
 
-The Clang Static Analyzer uses taint analysis to detect security-related issues in code.
-The backbone of taint analysis in the Clang SA is the `GenericTaintChecker`, which the user can access via the :ref:`alpha-security-taint-TaintPropagation` checker alias and this checker has a default taint-related configuration.
-The built-in default settings are defined in code, and they are always in effect once the checker is enabled, either directly or via the alias.
-The checker also provides a configuration interface for extending the default settings by providing a configuration file in `YAML <http://llvm.org/docs/YamlIO.html#introduction-to-yaml>`_ format.
+The Clang Static Analyzer uses taint analysis to detect injection vulnerability related issues in code.
+The backbone of taint analysis in the Clang SA is the ``TaintPropagation`` modeling checker.
+The reports are emitted via the :ref:`alpha-security-taint-GenericTaint` checker.
+The ``TaintPropagation`` checker has a default taint-related configuration.
+The built-in default settings are defined in code, and they are always in effect.
+The checker also provides a configuration interface for extending the default settings via the ``alpha.security.taint.TaintPropagation:Config`` checker config parameter
+by providing a configuration file to the in `YAML <http://llvm.org/docs/YamlIO.html#introduction-to-yaml>`_ format.
 This documentation describes the syntax of the configuration file and gives the informal semantics of the configuration options.
 
 .. contents::
@@ -18,7 +21,7 @@ ________
 
 Taint analysis works by checking for the occurrence of special operations during the symbolic execution of the program.
 Taint analysis defines sources, sinks, and propagation rules. It identifies errors by detecting a flow of information that originates from a taint source, reaches a taint sink, and propagates through the program paths via propagation rules.
-A source, sink, or an operation that propagates taint is mainly domain-specific knowledge, but there are some built-in defaults provided by :ref:`alpha-security-taint-TaintPropagation`.
+A source, sink, or an operation that propagates taint is mainly domain-specific knowledge, but there are some built-in defaults provided by the ``TaintPropagation`` checker.
 It is possible to express that a statement sanitizes tainted values by providing a ``Filters`` section in the external configuration (see :ref:`clangsa-taint-configuration-example` and :ref:`clangsa-taint-filter-details`).
 There are no default filters defined in the built-in settings.
 The checker's documentation also specifies how to provide a custom taint configuration with command-line options.

clang/include/clang/StaticAnalyzer/Checkers/Checkers.td

@@ -1071,7 +1071,7 @@ def ReturnPointerRangeChecker : Checker<"ReturnPtrRange">,
 
 let ParentPackage = Taint in {
 
-def GenericTaintChecker : Checker<"TaintPropagation">,
+def TaintPropagationChecker : Checker<"TaintPropagation">, // Modelling checker
   HelpText<"Generate taint information used by other checkers">,
   CheckerOptions<[
     CmdLineOption<String,
@@ -1080,6 +1080,12 @@ def GenericTaintChecker : Checker<"TaintPropagation">,
                   "",
                   InAlpha>,
   ]>,
+  Documentation<NotDocumented>,
+  Hidden;
+
+def GenericTaintChecker : Checker<"GenericTaint">,
+  HelpText<"Reports potential injection vulnerabilities">,
+  Dependencies<[TaintPropagationChecker]>,
   Documentation<HasDocumentation>;
 
 } // end "alpha.security.taint"
@@ -1717,9 +1723,7 @@ let ParentPackage = TaintOptIn in {
 def TaintedAllocChecker: Checker<"TaintedAlloc">,
   HelpText<"Check for memory allocations, where the size parameter "
            "might be a tainted (attacker controlled) value.">,
-  Dependencies<[DynamicMemoryModeling]>,
-  //FIXME: GenericTaintChecker should be a dependency, but only after it
-  //is transformed into a modeling checker
+  Dependencies<[DynamicMemoryModeling, TaintPropagationChecker]>,
   Documentation<HasDocumentation>;
 
 } // end "optin.taint"

clang/lib/StaticAnalyzer/Checkers/GenericTaintChecker.cpp

@@ -27,6 +27,7 @@
 #include "clang/StaticAnalyzer/Core/PathSensitive/CheckerContext.h"
 #include "clang/StaticAnalyzer/Core/PathSensitive/ProgramStateTrait.h"
 #include "llvm/ADT/StringExtras.h"
+#include "llvm/ADT/StringRef.h"
 #include "llvm/Support/YAMLTraits.h"
 
 #include <limits>
@@ -391,9 +392,10 @@ class GenericTaintChecker : public Checker<check::PreCall, check::PostCall> {
   bool generateReportIfTainted(const Expr *E, StringRef Msg,
                                CheckerContext &C) const;
 
-private:
-  const BugType BT{this, "Use of Untrusted Data", categories::TaintedData};
+  bool isTaintReporterCheckerEnabled = false;
+  std::optional<BugType> BT;
 
+private:
   bool checkUncontrolledFormatString(const CallEvent &Call,
                                      CheckerContext &C) const;
 
@@ -1033,20 +1035,23 @@ bool GenericTaintRule::UntrustedEnv(CheckerContext &C) {
 bool GenericTaintChecker::generateReportIfTainted(const Expr *E, StringRef Msg,
                                                   CheckerContext &C) const {
   assert(E);
+  if (!isTaintReporterCheckerEnabled)
+    return false;
   std::optional<SVal> TaintedSVal =
       getTaintedPointeeOrPointer(C.getState(), C.getSVal(E));
 
   if (!TaintedSVal)
     return false;
 
   // Generate diagnostic.
-  if (ExplodedNode *N = C.generateNonFatalErrorNode()) {
-    auto report = std::make_unique<PathSensitiveBugReport>(BT, Msg, N);
+  assert(BT);
+  static CheckerProgramPointTag Tag(BT->getCheckerName(), Msg);
+  if (ExplodedNode *N = C.generateNonFatalErrorNode(C.getState(), &Tag)) {
+    auto report = std::make_unique<PathSensitiveBugReport>(*BT, Msg, N);
     report->addRange(E->getSourceRange());
     for (auto TaintedSym : getTaintedSymbols(C.getState(), *TaintedSVal)) {
       report->markInteresting(TaintedSym);
     }
-
     C.emitReport(std::move(report));
     return true;
   }
@@ -1122,10 +1127,21 @@ void GenericTaintChecker::taintUnsafeSocketProtocol(const CallEvent &Call,
 }
 
 /// Checker registration
-void ento::registerGenericTaintChecker(CheckerManager &Mgr) {
+void ento::registerTaintPropagationChecker(CheckerManager &Mgr) {
   Mgr.registerChecker<GenericTaintChecker>();
 }
 
+bool ento::shouldRegisterTaintPropagationChecker(const CheckerManager &mgr) {
+  return true;
+}
+
+void ento::registerGenericTaintChecker(CheckerManager &Mgr) {
+  GenericTaintChecker *checker = Mgr.getChecker<GenericTaintChecker>();
+  checker->isTaintReporterCheckerEnabled = true;
+  checker->BT.emplace(Mgr.getCurrentCheckerName(), "Use of Untrusted Data",
+                      categories::TaintedData);
+}
+
 bool ento::shouldRegisterGenericTaintChecker(const CheckerManager &mgr) {
   return true;
 }