[X86] Added support for nocf_check attribute for indirect Branch Tracking

X86 Supports Indirect Branch Tracking (IBT) as part of Control-Flow Enforcement Technology (CET).
IBT instruments ENDBR instructions used to specify valid targets of indirect call / jmp.
The `nocf_check` attribute has two roles in the context of X86 IBT technology:
	1. Appertains to a function - do not add ENDBR instruction at the beginning of the function.
	2. Appertains to a function pointer - do not track the target function of this pointer by adding nocf_check prefix to the indirect-call instruction.

This patch implements `nocf_check` context for Indirect Branch Tracking.
It also auto generates `nocf_check` prefixes before indirect branchs to jump tables that are guarded by range checks.

Differential Revision: https://reviews.llvm.org/D41879

llvm-svn: 327767

1 files changed, 7 insertions, 0 deletions

diff --git a/llvm/lib/Target/X86/X86FastISel.cpp b/llvm/lib/Target/X86/X86FastISel.cpp
index 943022585a1..3806d2dad3d 100644
--- a/llvm/lib/Target/X86/X86FastISel.cpp
+++ b/llvm/lib/Target/X86/X86FastISel.cpp
@@ -3174,6 +3174,13 @@ bool X86FastISel::fastLowerCall(CallLoweringInfo &CLI) {
       CLI.CS ? dyn_cast<CallInst>(CLI.CS->getInstruction()) : nullptr;
   const Function *CalledFn = CI ? CI->getCalledFunction() : nullptr;
 
+  // Call / invoke instructions with NoCfCheck attribute require special
+  // handling.
+  const auto *II =
+      CLI.CS ? dyn_cast<InvokeInst>(CLI.CS->getInstruction()) : nullptr;
+  if ((CI && CI->doesNoCfCheck()) || (II && II->doesNoCfCheck()))
+    return false;
+
   // Functions with no_caller_saved_registers that need special handling.
   if ((CI && CI->hasFnAttr("no_caller_saved_registers")) ||
       (CalledFn && CalledFn->hasFnAttribute("no_caller_saved_registers")))