[AArch64] Return address signing B key support

- Add support to generate AUTIBSP, PACIBSP, RETAB instructions for return
  address signing
- The key used to sign the function is controlled by the function attribute
  "sign-return-address-key"

Differential Revision: https://reviews.llvm.org/D51427

llvm-svn: 345511

llvm/lib/Target/AArch64/AArch64FrameLowering.cpp

@@ -597,6 +597,17 @@ static void adaptForLdStOpt(MachineBasicBlock &MBB,
   //
 }
 
+static bool ShouldSignWithAKey(MachineFunction &MF) {
+  const Function &F = MF.getFunction();
+  if (!F.hasFnAttribute("sign-return-address-key"))
+    return true;
+
+  const StringRef Key =
+      F.getFnAttribute("sign-return-address-key").getValueAsString();
+  assert(Key.equals_lower("a_key") || Key.equals_lower("b_key"));
+  return Key.equals_lower("a_key");
+}
+
 void AArch64FrameLowering::emitPrologue(MachineFunction &MF,
                                         MachineBasicBlock &MBB) const {
   MachineBasicBlock::iterator MBBI = MBB.begin();
@@ -620,7 +631,9 @@ void AArch64FrameLowering::emitPrologue(MachineFunction &MF,
   DebugLoc DL;
 
   if (ShouldSignReturnAddress(MF)) {
-    BuildMI(MBB, MBBI, DL, TII->get(AArch64::PACIASP))
+    BuildMI(
+        MBB, MBBI, DL,
+        TII->get(ShouldSignWithAKey(MF) ? AArch64::PACIASP : AArch64::PACIBSP))
         .setMIFlag(MachineInstr::FrameSetup);
   }
 
@@ -907,10 +920,14 @@ static void InsertReturnAddressAuth(MachineFunction &MF,
   // instructions, namely RETA{A,B}, that can be used instead.
   if (Subtarget.hasV8_3aOps() && MBBI != MBB.end() &&
       MBBI->getOpcode() == AArch64::RET_ReallyLR) {
-    BuildMI(MBB, MBBI, DL, TII->get(AArch64::RETAA)).copyImplicitOps(*MBBI);
+    BuildMI(MBB, MBBI, DL,
+            TII->get(ShouldSignWithAKey(MF) ? AArch64::RETAA : AArch64::RETAB))
+        .copyImplicitOps(*MBBI);
     MBB.erase(MBBI);
   } else {
-    BuildMI(MBB, MBBI, DL, TII->get(AArch64::AUTIASP))
+    BuildMI(
+        MBB, MBBI, DL,
+        TII->get(ShouldSignWithAKey(MF) ? AArch64::AUTIASP : AArch64::AUTIBSP))
         .setMIFlag(MachineInstr::FrameDestroy);
   }
 }

llvm/test/CodeGen/AArch64/sign-return-address.ll

@@ -84,3 +84,26 @@ define fastcc void @spill_lr_and_tail_call(i64 %x) "sign-return-address"="all" {
   tail call fastcc i64 @bar(i64 %x)
   ret void
 }
+
+; CHECK-LABEL: @leaf_sign_all_a_key
+; CHECK: paciasp
+; CHECK: autiasp
+define i32 @leaf_sign_all_a_key(i32 %x) "sign-return-address"="all" "sign-return-address-key"="a_key" {
+  ret i32 %x
+}
+
+; CHECK-LABEL: @leaf_sign_all_b_key
+; CHECK: pacibsp
+; CHECK: autibsp
+define i32 @leaf_sign_all_b_key(i32 %x) "sign-return-address"="all" "sign-return-address-key"="b_key" {
+  ret i32 %x
+}
+
+; CHECK-LABEL: @leaf_sign_all_v83_b_key
+; CHECK: pacibsp
+; CHECK-NOT: ret
+; CHECK: retab
+; CHECK-NOT: ret
+define i32 @leaf_sign_all_v83_b_key(i32 %x) "sign-return-address"="all" "target-features"="+v8.3a" "sign-return-address-key"="b_key" {
+  ret i32 %x
+}