[clang] [clang][analyzer] MmapWriteExecChecker improvements (PR #97078)

[Balázs Kéri via cfe-commits]

================
@@ -21,30 +21,55 @@
 #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/CheckerHelpers.h"
 
 using namespace clang;
 using namespace ento;
 
 namespace {
-class MmapWriteExecChecker : public Checker<check::PreCall> {
+class MmapWriteExecChecker
+    : public Checker<check::BeginFunction, check::PreCall> {
   CallDescription MmapFn{CDM::CLibrary, {"mmap"}, 6};
   CallDescription MprotectFn{CDM::CLibrary, {"mprotect"}, 3};
-  static int ProtWrite;
-  static int ProtExec;
-  static int ProtRead;
   const BugType BT{this, "W^X check fails, Write Exec prot flags set",
                    "Security"};
 
+  mutable bool FlagsInitialized = false;
+  mutable int ProtRead = 0x01;
+  mutable int ProtWrite = 0x02;
+  mutable int ProtExec = 0x04;
+
 public:
+  void checkBeginFunction(CheckerContext &C) const;
   void checkPreCall(const CallEvent &Call, CheckerContext &C) const;
+
   int ProtExecOv;
   int ProtReadOv;
 };
 }
 
-int MmapWriteExecChecker::ProtWrite = 0x02;
-int MmapWriteExecChecker::ProtExec  = 0x04;
-int MmapWriteExecChecker::ProtRead  = 0x01;
+void MmapWriteExecChecker::checkBeginFunction(CheckerContext &C) const {
+  if (FlagsInitialized)
+    return;
+
+  FlagsInitialized = true;
+
+  const std::optional<int> FoundProtRead =
+          tryExpandAsInteger("PROT_READ", C.getPreprocessor());
+  const std::optional<int> FoundProtWrite =
+          tryExpandAsInteger("PROT_WRITE", C.getPreprocessor());
+  const std::optional<int> FoundProtExec =
+          tryExpandAsInteger("PROT_EXEC", C.getPreprocessor());
+  if (FoundProtRead && FoundProtWrite && FoundProtExec) {
+    ProtRead = *FoundProtRead;
+    ProtWrite = *FoundProtWrite;
+    ProtExec = *FoundProtExec;
+  } else {
+    // FIXME: Are these useful?
+    ProtRead = ProtReadOv;
+    ProtExec = ProtExecOv;
----------------
balazske wrote:

My problem was that why is `PROT_WRITE` missing. If the flags are specified it is meaningful only to pass all 3 values, otherwise it may cause malfunction of the checker. From the test file it looks like that this is only used to swap values of `PROT_EXEC` and `PROT_READ`, probably some platforms need this specific change. But then a single option `SwapDefaultReadExecFlags` would be more useful. I could add a third option for `PROT_WRITE` or remove all of these.

https://github.com/llvm/llvm-project/pull/97078