[clang] [clang] Wire -fptrauth-returns to "ptrauth-returns" fn attribute. (PR #102416)

[Ahmed Bougacha via cfe-commits]

https://github.com/ahmedbougacha created https://github.com/llvm/llvm-project/pull/102416

We already ended up with -fptrauth-returns, the feature macro, the lang opt, and the actual backend lowering.

The only part left is threading it all through PointerAuthOptions, to drive the addition of the "ptrauth-returns" attribute to generated functions.

This also adds ptrauth_key_return_address to ptrauth.h.

>From 41061b347b7d0fa862f65896d4fc155cb0b791ba Mon Sep 17 00:00:00 2001
From: Ahmed Bougacha <ahmed at bougacha.org>
Date: Fri, 24 May 2024 20:24:26 -0700
Subject: [PATCH] [clang] Wire -fptrauth-returns to "ptrauth-returns" fn
 attribute.

We already ended up with -fptrauth-returns, the feature macro, the lang
opt, and the actual backend lowering.

The only part left is threading it all through PointerAuthOptions, to
drive the addition of the "ptrauth-returns" attribute to generated
functions.

This also adds ptrauth_key_return_address to ptrauth.h.
---
 clang/include/clang/Basic/PointerAuthOptions.h | 3 +++
 clang/lib/CodeGen/CodeGenFunction.cpp          | 2 ++
 clang/lib/Frontend/CompilerInvocation.cpp      | 4 +++-
 clang/lib/Headers/ptrauth.h                    | 6 ++++++
 4 files changed, 14 insertions(+), 1 deletion(-)

diff --git a/clang/include/clang/Basic/PointerAuthOptions.h b/clang/include/clang/Basic/PointerAuthOptions.h
index 8f63cf2ad2bf27..a847bf4a4b4f6d 100644
--- a/clang/include/clang/Basic/PointerAuthOptions.h
+++ b/clang/include/clang/Basic/PointerAuthOptions.h
@@ -163,6 +163,9 @@ class PointerAuthSchema {
 };
 
 struct PointerAuthOptions {
+  /// Should return addresses be authenticated?
+  bool ReturnAddresses = false;
+
   /// Do indirect goto label addresses need to be authenticated?
   bool IndirectGotos = false;
 
diff --git a/clang/lib/CodeGen/CodeGenFunction.cpp b/clang/lib/CodeGen/CodeGenFunction.cpp
index af201554898f31..4dc57d0ff5b269 100644
--- a/clang/lib/CodeGen/CodeGenFunction.cpp
+++ b/clang/lib/CodeGen/CodeGenFunction.cpp
@@ -880,6 +880,8 @@ void CodeGenFunction::StartFunction(GlobalDecl GD, QualType RetTy,
 
   // Add pointer authentication attributes.
   const CodeGenOptions &CodeGenOpts = CGM.getCodeGenOpts();
+  if (CodeGenOpts.PointerAuth.ReturnAddresses)
+    Fn->addFnAttr("ptrauth-returns");
   if (CodeGenOpts.PointerAuth.FunctionPointers)
     Fn->addFnAttr("ptrauth-calls");
   if (CodeGenOpts.PointerAuth.IndirectGotos)
diff --git a/clang/lib/Frontend/CompilerInvocation.cpp b/clang/lib/Frontend/CompilerInvocation.cpp
index 225bd6416ce5fc..e206cfe4172616 100644
--- a/clang/lib/Frontend/CompilerInvocation.cpp
+++ b/clang/lib/Frontend/CompilerInvocation.cpp
@@ -1511,13 +1511,15 @@ void CompilerInvocation::setDefaultPointerAuthOptions(
     }
   }
   Opts.IndirectGotos = LangOpts.PointerAuthIndirectGotos;
+  Opts.ReturnAddresses = LangOpts.PointerAuthReturns;
 }
 
 static void parsePointerAuthOptions(PointerAuthOptions &Opts,
                                     const LangOptions &LangOpts,
                                     const llvm::Triple &Triple,
                                     DiagnosticsEngine &Diags) {
-  if (!LangOpts.PointerAuthCalls && !LangOpts.PointerAuthIndirectGotos)
+  if (!LangOpts.PointerAuthCalls && !LangOpts.PointerAuthIndirectGotos &&
+      !LangOpts.PointerAuthReturns)
     return;
 
   CompilerInvocation::setDefaultPointerAuthOptions(Opts, LangOpts, Triple);
diff --git a/clang/lib/Headers/ptrauth.h b/clang/lib/Headers/ptrauth.h
index 6cbdccff9a4c16..d489a67c533d41 100644
--- a/clang/lib/Headers/ptrauth.h
+++ b/clang/lib/Headers/ptrauth.h
@@ -28,6 +28,12 @@ typedef enum {
   /* A process-specific key which can be used to sign data pointers. */
   ptrauth_key_process_dependent_data = ptrauth_key_asdb,
 
+  /* The key used to sign return addresses on the stack.
+     The extra data is based on the storage address of the return address.
+     On AArch64, that is always the storage address of the return address + 8
+     (or, in other words, the value of the stack pointer on function entry) */
+  ptrauth_key_return_address = ptrauth_key_process_dependent_code,
+
   /* The key used to sign C function pointers.
      The extra data is always 0. */
   ptrauth_key_function_pointer = ptrauth_key_process_independent_code,