[clang][Obj-C][PAC] Make block descriptor pointer signing configurable

[ojhunt]

Pointer auth protection of the block descriptor pointer is only supported in some constrained environments so we do actually need it to be configurable.

We had made it non configurable in the first PR to protect block metadata because we believed that was an option but subsequently realised it does need to remain configurable.

This PR revives the flags that permit this.

[llvmbot]

@llvm/pr-subscribers-clang

Author: Oliver Hunt (ojhunt)

Changes

Pointer auth protection of the block descriptor pointer is only supported in some constrained environments so we do actually need it to be configurable.

We had made it non configurable in the first PR to protect block metadata because we believed that was an option but subsequently realised it does need to remain configurable.

This PR revives the flags that permit this.

---

Full diff: https://github.com/llvm/llvm-project/pull/153700.diff

6 Files Affected:

• (modified) clang/include/clang/Basic/Features.def (+1-1)
• (modified) clang/include/clang/Basic/LangOptions.def (+2)
• (modified) clang/include/clang/Driver/Options.td (+1)
• (modified) clang/lib/Frontend/CompilerInvocation.cpp (+8-3)
• (modified) clang/test/CodeGenObjC/ptrauth-block-descriptor-pointer.m (+1-1)
• (modified) clang/test/CodeGenObjC/ptrauth-block-isa.m (+1-1)

diff --git a/clang/include/clang/Basic/Features.def b/clang/include/clang/Basic/Features.def
index 0f6cd005bfd03..b9efc6a6a2e9d 100644
--- a/clang/include/clang/Basic/Features.def
+++ b/clang/include/clang/Basic/Features.def
@@ -155,7 +155,7 @@ FEATURE(ptrauth_vtable_pointer_address_discrimination, LangOpts.PointerAuthVTPtr
 FEATURE(ptrauth_vtable_pointer_type_discrimination, LangOpts.PointerAuthVTPtrTypeDiscrimination)
 FEATURE(ptrauth_type_info_vtable_pointer_discrimination, LangOpts.PointerAuthTypeInfoVTPtrDiscrimination)
 FEATURE(ptrauth_member_function_pointer_type_discrimination, LangOpts.PointerAuthCalls)
-FEATURE(ptrauth_signed_block_descriptors, LangOpts.PointerAuthCalls)
+FEATURE(ptrauth_signed_block_descriptors, LangOpts.PointerAuthBlockDescriptorPointers)
 FEATURE(ptrauth_function_pointer_type_discrimination, LangOpts.PointerAuthFunctionTypeDiscrimination)
 FEATURE(ptrauth_indirect_gotos, LangOpts.PointerAuthIndirectGotos)
 FEATURE(ptrauth_init_fini, LangOpts.PointerAuthInitFini)
diff --git a/clang/include/clang/Basic/LangOptions.def b/clang/include/clang/Basic/LangOptions.def
index 08d98a77e0252..f094ba112988f 100644
--- a/clang/include/clang/Basic/LangOptions.def
+++ b/clang/include/clang/Basic/LangOptions.def
@@ -136,6 +136,8 @@ LANGOPT(PointerAuthObjcInterfaceSel, 1, 0, NotCompatible, "authentication of SEL
 LANGOPT(PointerAuthObjcInterfaceSelKey, 16, 0, NotCompatible, "authentication key for SEL fields of ObjC interfaces")
 LANGOPT(PointerAuthObjcClassROPointers, 1, 0, Benign, "class_ro_t pointer authentication")
 
+LANGOPT(PointerAuthBlockDescriptorPointers, 1, 0, NotCompatible, "enable signed block descriptors")
+
 LANGOPT(DoubleSquareBracketAttributes, 1, 0, NotCompatible, "'[[]]' attributes extension for all language standard modes")
 LANGOPT(ExperimentalLateParseAttributes, 1, 0, NotCompatible, "experimental late parsing of attributes")
 
diff --git a/clang/include/clang/Driver/Options.td b/clang/include/clang/Driver/Options.td
index 7712a49cef154..858f37c392107 100644
--- a/clang/include/clang/Driver/Options.td
+++ b/clang/include/clang/Driver/Options.td
@@ -4546,6 +4546,7 @@ defm aarch64_jump_table_hardening: OptInCC1FFlag<"aarch64-jump-table-hardening",
 defm ptrauth_objc_isa : OptInCC1FFlag<"ptrauth-objc-isa", "Enable signing and authentication of Objective-C object's 'isa' field">;
 defm ptrauth_objc_interface_sel : OptInCC1FFlag<"ptrauth-objc-interface-sel", "Enable signing and authentication of Objective-C object's 'SEL' fields">;
 defm ptrauth_objc_class_ro : OptInCC1FFlag<"ptrauth-objc-class-ro", "Enable signing and authentication for ObjC class_ro pointers">;
+defm ptrauth_block_descriptor_pointers : OptInCC1FFlag<"ptrauth-block-descriptor-pointers", "Enable signing and authentication of block descriptors">;
 }
 
 def fenable_matrix : Flag<["-"], "fenable-matrix">, Group<f_Group>,
diff --git a/clang/lib/Frontend/CompilerInvocation.cpp b/clang/lib/Frontend/CompilerInvocation.cpp
index a4d18966be35f..da96352e1d82c 100644
--- a/clang/lib/Frontend/CompilerInvocation.cpp
+++ b/clang/lib/Frontend/CompilerInvocation.cpp
@@ -1548,9 +1548,10 @@ void CompilerInvocation::setDefaultPointerAuthOptions(
         PointerAuthSchema(Key::ASIA, true, Discrimination::None);
     Opts.BlockByrefHelperFunctionPointers =
         PointerAuthSchema(Key::ASIA, true, Discrimination::None);
-    Opts.BlockDescriptorPointers =
-        PointerAuthSchema(Key::ASDA, true, Discrimination::Constant,
-                          BlockDescriptorConstantDiscriminator);
+    if (LangOpts.PointerAuthBlockDescriptorPointers)
+      Opts.BlockDescriptorPointers =
+          PointerAuthSchema(Key::ASDA, true, Discrimination::Constant,
+                            BlockDescriptorConstantDiscriminator);
 
     Opts.ObjCMethodListFunctionPointers =
         PointerAuthSchema(Key::ASIA, true, Discrimination::None);
@@ -3608,6 +3609,8 @@ static void GeneratePointerAuthArgs(const LangOptions &Opts,
     GenerateArg(Consumer, OPT_fptrauth_objc_interface_sel);
   if (Opts.PointerAuthObjcClassROPointers)
     GenerateArg(Consumer, OPT_fptrauth_objc_class_ro);
+  if (Opts.PointerAuthBlockDescriptorPointers)
+    GenerateArg(Consumer, OPT_fptrauth_block_descriptor_pointers);
 }
 
 static void ParsePointerAuthArgs(LangOptions &Opts, ArgList &Args,
@@ -3631,6 +3634,8 @@ static void ParsePointerAuthArgs(LangOptions &Opts, ArgList &Args,
   Opts.PointerAuthELFGOT = Args.hasArg(OPT_fptrauth_elf_got);
   Opts.AArch64JumpTableHardening =
       Args.hasArg(OPT_faarch64_jump_table_hardening);
+  Opts.PointerAuthBlockDescriptorPointers =
+      Args.hasArg(OPT_fptrauth_block_descriptor_pointers);
   Opts.PointerAuthObjcIsa = Args.hasArg(OPT_fptrauth_objc_isa);
   Opts.PointerAuthObjcClassROPointers = Args.hasArg(OPT_fptrauth_objc_class_ro);
   Opts.PointerAuthObjcInterfaceSel =
diff --git a/clang/test/CodeGenObjC/ptrauth-block-descriptor-pointer.m b/clang/test/CodeGenObjC/ptrauth-block-descriptor-pointer.m
index 559cddfd4e866..f852c6d93fd58 100644
--- a/clang/test/CodeGenObjC/ptrauth-block-descriptor-pointer.m
+++ b/clang/test/CodeGenObjC/ptrauth-block-descriptor-pointer.m
@@ -1,4 +1,4 @@
-// RUN: %clang_cc1 -fobjc-arc -fblocks -fptrauth-calls -triple arm64e-apple-ios  -emit-llvm -o - %s | FileCheck %s
+// RUN: %clang_cc1 -fobjc-arc -fblocks -fptrauth-calls -fptrauth-block-descriptor-pointers -triple arm64e-apple-ios  -emit-llvm -o - %s | FileCheck %s
 
 _Static_assert(__has_feature(ptrauth_signed_block_descriptors), "-fptrauth-block-descriptor-pointers should set ptrauth_signed_block_descriptors");
 
diff --git a/clang/test/CodeGenObjC/ptrauth-block-isa.m b/clang/test/CodeGenObjC/ptrauth-block-isa.m
index c37fe8b0d7fec..248e57769ba1e 100644
--- a/clang/test/CodeGenObjC/ptrauth-block-isa.m
+++ b/clang/test/CodeGenObjC/ptrauth-block-isa.m
@@ -2,7 +2,7 @@
 
 void (^globalblock)(void) = ^{};
 // CHECK: [[BLOCK_DESCRIPTOR_NAME:@"__block_descriptor_.*"]] = linkonce_odr hidden unnamed_addr constant { i64, i64, ptr, ptr } { i64 0, i64 32, ptr @.str, ptr null }, comdat, align 8
-// CHECK: @__block_literal_global = internal constant { ptr, i32, i32, ptr, ptr } { ptr ptrauth (ptr @_NSConcreteGlobalBlock, i32 2, i64 27361, ptr @__block_literal_global), i32 1342177280, i32 0, ptr ptrauth (ptr @globalblock_block_invoke, i32 0, i64 0, ptr getelementptr inbounds ({ ptr, i32, i32, ptr, ptr }, ptr @__block_literal_global, i32 0, i32 3)), ptr ptrauth (ptr [[BLOCK_DESCRIPTOR_NAME]], i32 2, i64 49339, ptr getelementptr inbounds ({ ptr, i32, i32, ptr, ptr }, ptr @__block_literal_global, i32 0, i32 4)) }
+// CHECK: @__block_literal_global = internal constant { ptr, i32, i32, ptr, ptr } { ptr ptrauth (ptr @_NSConcreteGlobalBlock, i32 2, i64 27361, ptr @__block_literal_global), i32 1342177280, i32 0, ptr ptrauth (ptr @globalblock_block_invoke, i32 0, i64 0, ptr getelementptr inbounds ({ ptr, i32, i32, ptr, ptr }, ptr @__block_literal_global, i32 0, i32 3)), ptr [[BLOCK_DESCRIPTOR_NAME]] }
 
 @interface A
 - (int) count;