1 files changed, 126 insertions, 0 deletions
diff --git a/contrib/llvm-project/llvm/lib/CodeGen/AsmPrinter/WinCFGuard.cpp b/contrib/llvm-project/llvm/lib/CodeGen/AsmPrinter/WinCFGuard.cpp
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index 000000000000..1a1e6f0117e2
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+++ b/contrib/llvm-project/llvm/lib/CodeGen/AsmPrinter/WinCFGuard.cpp
@@ -0,0 +1,126 @@
+//===-- CodeGen/AsmPrinter/WinCFGuard.cpp - Control Flow Guard Impl ------===//
+//
+// 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 file contains support for writing the metadata for Windows Control Flow
+// Guard, including address-taken functions and valid longjmp targets.
+//
+//===----------------------------------------------------------------------===//
+
+#include "WinCFGuard.h"
+#include "llvm/CodeGen/AsmPrinter.h"
+#include "llvm/CodeGen/MachineFunction.h"
+#include "llvm/CodeGen/MachineModuleInfo.h"
+#include "llvm/IR/Constants.h"
+#include "llvm/IR/InstrTypes.h"
+#include "llvm/IR/Module.h"
+#include "llvm/MC/MCObjectFileInfo.h"
+#include "llvm/MC/MCStreamer.h"
+
+#include <vector>
+
+using namespace llvm;
+
+WinCFGuard::WinCFGuard(AsmPrinter *A) : Asm(A) {}
+
+WinCFGuard::~WinCFGuard() = default;
+
+void WinCFGuard::endFunction(const MachineFunction *MF) {
+
+  // Skip functions without any longjmp targets.
+  if (MF->getLongjmpTargets().empty())
+    return;
+
+  // Copy the function's longjmp targets to a module-level list.
+  llvm::append_range(LongjmpTargets, MF->getLongjmpTargets());
+}
+
+/// Returns true if this function's address is escaped in a way that might make
+/// it an indirect call target. Function::hasAddressTaken gives different
+/// results when a function is called directly with a function prototype
+/// mismatch, which requires a cast.
+static bool isPossibleIndirectCallTarget(const Function *F) {
+  SmallVector<const Value *, 4> Users{F};
+  while (!Users.empty()) {
+    const Value *FnOrCast = Users.pop_back_val();
+    for (const Use &U : FnOrCast->uses()) {
+      const User *FnUser = U.getUser();
+      if (isa<BlockAddress>(FnUser))
+        continue;
+      if (const auto *Call = dyn_cast<CallBase>(FnUser)) {
+        if (!Call->isCallee(&U))
+          return true;
+      } else if (isa<Instruction>(FnUser)) {
+        // Consider any other instruction to be an escape. This has some weird
+        // consequences like no-op intrinsics being an escape or a store *to* a
+        // function address being an escape.
+        return true;
+      } else if (const auto *C = dyn_cast<Constant>(FnUser)) {
+        // If this is a constant pointer cast of the function, don't consider
+        // this escape. Analyze the uses of the cast as well. This ensures that
+        // direct calls with mismatched prototypes don't end up in the CFG
+        // table. Consider other constants, such as vtable initializers, to
+        // escape the function.
+        if (C->stripPointerCasts() == F)
+          Users.push_back(FnUser);
+        else
+          return true;
+      }
+    }
+  }
+  return false;
+}
+
+MCSymbol *WinCFGuard::lookupImpSymbol(const MCSymbol *Sym) {
+  if (Sym->getName().starts_with("__imp_"))
+    return nullptr;
+  return Asm->OutContext.lookupSymbol(Twine("__imp_") + Sym->getName());
+}
+
+void WinCFGuard::endModule() {
+  const Module *M = Asm->MMI->getModule();
+  std::vector<const MCSymbol *> GFIDsEntries;
+  std::vector<const MCSymbol *> GIATsEntries;
+  for (const Function &F : *M) {
+    if (isPossibleIndirectCallTarget(&F)) {
+      // If F is a dllimport and has an "__imp_" symbol already defined, add the
+      // "__imp_" symbol to the .giats section.
+      if (F.hasDLLImportStorageClass()) {
+        if (MCSymbol *impSym = lookupImpSymbol(Asm->getSymbol(&F))) {
+          GIATsEntries.push_back(impSym);
+        }
+      }
+      // Add the function's symbol to the .gfids section.
+      // Note: For dllimport functions, MSVC sometimes does not add this symbol
+      // to the .gfids section, but only adds the corresponding "__imp_" symbol
+      // to the .giats section. Here we always add the symbol to the .gfids
+      // section, since this does not introduce security risks.
+      GFIDsEntries.push_back(Asm->getSymbol(&F));
+    }
+  }
+
+  if (GFIDsEntries.empty() && GIATsEntries.empty() && LongjmpTargets.empty())
+    return;
+
+  // Emit the symbol index of each GFIDs entry to form the .gfids section.
+  auto &OS = *Asm->OutStreamer;
+  OS.switchSection(Asm->OutContext.getObjectFileInfo()->getGFIDsSection());
+  for (const MCSymbol *S : GFIDsEntries)
+    OS.emitCOFFSymbolIndex(S);
+
+  // Emit the symbol index of each GIATs entry to form the .giats section.
+  OS.switchSection(Asm->OutContext.getObjectFileInfo()->getGIATsSection());
+  for (const MCSymbol *S : GIATsEntries) {
+    OS.emitCOFFSymbolIndex(S);
+  }
+
+  // Emit the symbol index of each longjmp target to form the .gljmp section.
+  OS.switchSection(Asm->OutContext.getObjectFileInfo()->getGLJMPSection());
+  for (const MCSymbol *S : LongjmpTargets) {
+    OS.emitCOFFSymbolIndex(S);
+  }
+}