[PATCH] D140655: [LowerTypeTests] Add ENDBR to .cfi.jumptable for x86 Indirect Branch Tracking

[Fangrui Song via Phabricator via llvm-commits]

MaskRay created this revision.
MaskRay added reviewers: eugenis, pcc, tejohnson.
Herald added subscribers: ormris, StephenFan, hiraditya, kristof.beyls.
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Similar D81251 <https://reviews.llvm.org/D81251> for AArch64 BTI.

This fixes `./a.out test` for

  void foo(void) {}
  void bar(void) {}
  static void (*fptr)(void);
  int main(int argc, char **argv) {
    if (argv[1]) fptr = foo;
    else fptr = bar;
    fptr();
  }

`clang -flto=thin -fvisibility=hidden -fsanitize=cfi-icall -fcf-protection=branch -fuse-ld=lld a.cc`


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D140655

Files:
  llvm/lib/Transforms/IPO/LowerTypeTests.cpp
  llvm/test/Transforms/LowerTypeTests/x86-jumptable.ll


Index: llvm/test/Transforms/LowerTypeTests/x86-jumptable.ll
===================================================================
--- /dev/null
+++ llvm/test/Transforms/LowerTypeTests/x86-jumptable.ll
@@ -0,0 +1,31 @@
+;; Test jump table generation with Indirect Branch Tracking on x86.
+; RUN: opt -S -passes=lowertypetests -mtriple=i686 %s | FileCheck --check-prefixes=X86,X86_32 %s
+; RUN: opt -S -passes=lowertypetests -mtriple=x86_64 %s | FileCheck --check-prefixes=X86,X86_64 %s
+
+ at 0 = private unnamed_addr constant [2 x ptr] [ptr @f, ptr @g], align 16
+
+define void @f() !type !0 {
+  ret void
+}
+
+define internal void @g() !type !0 {
+  ret void
+}
+
+declare i1 @llvm.type.test(ptr %ptr, metadata %bitset) nounwind readnone
+
+define i1 @foo(ptr %p) {
+  %x = call i1 @llvm.type.test(ptr %p, metadata !"typeid1")
+  ret i1 %x
+}
+
+!llvm.module.flags = !{!1}
+!0 = !{i32 0, !"typeid1"}
+!1 = !{i32 8, !"cf-protection-branch", i32 1}
+
+; X86:         define private void @.cfi.jumptable() #[[#ATTR:]] align 16 {
+; X86-NEXT:    entry:
+; X86_32-NEXT:   call void asm sideeffect "endbr32\0Ajmp ${0:c}@plt\0A.balign 16, 0xcc\0Aendbr32\0Ajmp ${1:c}@plt\0A.balign 16, 0xcc\0A", "s,s"(ptr @f.cfi, ptr @g.cfi)
+; X86_64-NEXT:   call void asm sideeffect "endbr64\0Ajmp ${0:c}@plt\0A.balign 16, 0xcc\0Aendbr64\0Ajmp ${1:c}@plt\0A.balign 16, 0xcc\0A", "s,s"(ptr @f.cfi, ptr @g.cfi)
+
+; X86_64: attributes #[[#ATTR]] = { naked nocf_check nounwind }
Index: llvm/lib/Transforms/IPO/LowerTypeTests.cpp
===================================================================
--- llvm/lib/Transforms/IPO/LowerTypeTests.cpp
+++ llvm/lib/Transforms/IPO/LowerTypeTests.cpp
@@ -1179,6 +1179,7 @@
 }
 
 static const unsigned kX86JumpTableEntrySize = 8;
+static const unsigned kX86IBTJumpTableEntrySize = 16;
 static const unsigned kARMJumpTableEntrySize = 4;
 static const unsigned kARMBTIJumpTableEntrySize = 8;
 static const unsigned kRISCVJumpTableEntrySize = 8;
@@ -1187,6 +1188,10 @@
   switch (Arch) {
     case Triple::x86:
     case Triple::x86_64:
+      if (const auto *MD = mdconst::extract_or_null<ConstantInt>(
+            M.getModuleFlag("cf-protection-branch")))
+        if (MD->getZExtValue())
+          return kX86IBTJumpTableEntrySize;
       return kX86JumpTableEntrySize;
     case Triple::arm:
     case Triple::thumb:
@@ -1215,8 +1220,17 @@
   unsigned ArgIndex = AsmArgs.size();
 
   if (JumpTableArch == Triple::x86 || JumpTableArch == Triple::x86_64) {
+    bool Endbr = false;
+    if (const auto *MD = mdconst::extract_or_null<ConstantInt>(
+          Dest->getParent()->getModuleFlag("cf-protection-branch")))
+      Endbr = MD->getZExtValue() != 0;
+    if (Endbr)
+      AsmOS << (JumpTableArch == Triple::x86 ? "endbr32\n" : "endbr64\n");
     AsmOS << "jmp ${" << ArgIndex << ":c}@plt\n";
-    AsmOS << "int3\nint3\nint3\n";
+    if (Endbr)
+      AsmOS << ".balign 16, 0xcc\n";
+    else
+      AsmOS << "int3\nint3\nint3\n";
   } else if (JumpTableArch == Triple::arm) {
     AsmOS << "b $" << ArgIndex << "\n";
   } else if (JumpTableArch == Triple::aarch64) {
@@ -1398,6 +1412,8 @@
     // the linker.
     F->addFnAttr("target-features", "-c,-relax");
   }
+  if (JumpTableArch == Triple::x86 || JumpTableArch == Triple::x86_64)
+    F->addFnAttr(Attribute::NoCfCheck);
   // Make sure we don't emit .eh_frame for this function.
   F->addFnAttr(Attribute::NoUnwind);
 


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