Add Forward Control-Flow Integrity.

This commit adds a new pass that can inject checks before indirect calls to
make sure that these calls target known locations. It supports three types of
checks and, at compile time, it can take the name of a custom function to call
when an indirect call check fails. The default failure function ignores the
error and continues.

This pass incidentally moves the function JumpInstrTables::transformType from
private to public and makes it static (with a new argument that specifies the
table type to use); this is so that the CFI code can transform function types
at call sites to determine which jump-instruction table to use for the check at
that site.

Also, this removes support for jumptables in ARM, pending further performance
analysis and discussion.

Review: http://reviews.llvm.org/D4167
llvm-svn: 221708

2 files changed, 18 insertions, 0 deletions

diff --git a/llvm/lib/Target/X86/X86InstrInfo.cpp b/llvm/lib/Target/X86/X86InstrInfo.cpp
index 68c5ff44ca9..12de514a3d3 100644
--- a/llvm/lib/Target/X86/X86InstrInfo.cpp
+++ b/llvm/lib/Target/X86/X86InstrInfo.cpp
@@ -5477,16 +5477,32 @@ void X86InstrInfo::getNoopForMachoTarget(MCInst &NopInst) const {
   NopInst.setOpcode(X86::NOOP);
 }
 
+// This code must remain in sync with getJumpInstrTableEntryBound in this class!
+// In particular, getJumpInstrTableEntryBound must always return an upper bound
+// on the encoding lengths of the instructions generated by
+// getUnconditionalBranch and getTrap.
 void X86InstrInfo::getUnconditionalBranch(
     MCInst &Branch, const MCSymbolRefExpr *BranchTarget) const {
   Branch.setOpcode(X86::JMP_4);
   Branch.addOperand(MCOperand::CreateExpr(BranchTarget));
 }
 
+// This code must remain in sync with getJumpInstrTableEntryBound in this class!
+// In particular, getJumpInstrTableEntryBound must always return an upper bound
+// on the encoding lengths of the instructions generated by
+// getUnconditionalBranch and getTrap.
 void X86InstrInfo::getTrap(MCInst &MI) const {
   MI.setOpcode(X86::TRAP);
 }
 
+// See getTrap and getUnconditionalBranch for conditions on the value returned
+// by this function.
+unsigned X86InstrInfo::getJumpInstrTableEntryBound() const {
+  // 5 bytes suffice: JMP_4 Symbol@PLT is uses 1 byte (E9) for the JMP_4 and 4
+  // bytes for the symbol offset. And TRAP is ud2, which is two bytes (0F 0B).
+  return 5;
+}
+
 bool X86InstrInfo::isHighLatencyDef(int opc) const {
   switch (opc) {
   default: return false;
diff --git a/llvm/lib/Target/X86/X86InstrInfo.h b/llvm/lib/Target/X86/X86InstrInfo.h
index f3f54ae5664..57b19589545 100644
--- a/llvm/lib/Target/X86/X86InstrInfo.h
+++ b/llvm/lib/Target/X86/X86InstrInfo.h
@@ -413,6 +413,8 @@ public:
 
   void getTrap(MCInst &MI) const override;
 
+  unsigned getJumpInstrTableEntryBound() const override;
+
   bool isHighLatencyDef(int opc) const override;
 
   bool hasHighOperandLatency(const InstrItineraryData *ItinData,