From: mortimer <mortimer@openbsd.org>
Date: Wed, 1 Sep 2021 13:37:14 +0000 (+0000)
Subject: Add lfence after ret in retpoline thunk.
X-Git-Url: http://artulab.com/gitweb/?a=commitdiff_plain;h=d23869897606b8e31c73d9c35bc87b8dc53e8483;p=openbsd

Add lfence after ret in retpoline thunk.

Recommended by AMD white paper Software Techniques for Managing
Speculation on AMD Processors (9.17.20) mitigation V2-1.

Pointed out by bluhm@. ok bluhm@ kettenis@
---

diff --git a/gnu/llvm/llvm/lib/Target/X86/X86IndirectThunks.cpp b/gnu/llvm/llvm/lib/Target/X86/X86IndirectThunks.cpp
index 828887d9612..ae26ed481c2 100644
--- a/gnu/llvm/llvm/lib/Target/X86/X86IndirectThunks.cpp
+++ b/gnu/llvm/llvm/lib/Target/X86/X86IndirectThunks.cpp
@@ -250,6 +250,7 @@ void RetpolineThunkInserter::populateThunk(MachineFunction &MF) {
 
   CallTarget->back().setPreInstrSymbol(MF, TargetSym);
   BuildMI(CallTarget, DebugLoc(), TII->get(RetOpc));
+  BuildMI(CallTarget, DebugLoc(), TII->get(X86::LFENCE));
 }
 
 FunctionPass *llvm::createX86IndirectThunksPass() {