[PATCH] D141172: [ModuleUtils][KCFI] Set patchable-function-prefix for synthesized functions

[Sami Tolvanen via Phabricator via llvm-commits]

samitolvanen updated this revision to Diff 487536.
samitolvanen marked an inline comment as done.
samitolvanen added a comment.

Addressed feedback.


Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D141172/new/

https://reviews.llvm.org/D141172

Files:
  clang/lib/CodeGen/CodeGenModule.cpp
  clang/test/CodeGen/kcfi.c
  llvm/lib/Transforms/Utils/ModuleUtils.cpp
  llvm/test/Instrumentation/AddressSanitizer/kcfi-offset.ll


Index: llvm/test/Instrumentation/AddressSanitizer/kcfi-offset.ll
===================================================================
--- /dev/null
+++ llvm/test/Instrumentation/AddressSanitizer/kcfi-offset.ll
@@ -0,0 +1,15 @@
+;; Test that we set patchable-function-prefix for asan.module_ctor when kcfi-offset is defined.
+
+; RUN: opt < %s -passes=asan -S | FileCheck %s
+
+; CHECK: @llvm.global_ctors = {{.*}}{ i32 1, ptr @asan.module_ctor, ptr @asan.module_ctor }
+
+; CHECK: define internal void @asan.module_ctor()
+; CHECK-SAME: #[[#ATTR:]]
+; CHECK-SAME: !kcfi_type
+
+; CHECK: attributes #[[#ATTR]] = { {{.*}} "patchable-function-prefix"="3" }
+
+!llvm.module.flags = !{!0, !1}
+!0 = !{i32 4, !"kcfi", i32 1}
+!1 = !{i32 4, !"kcfi-offset", i32 3}
Index: llvm/lib/Transforms/Utils/ModuleUtils.cpp
===================================================================
--- llvm/lib/Transforms/Utils/ModuleUtils.cpp
+++ llvm/lib/Transforms/Utils/ModuleUtils.cpp
@@ -161,6 +161,13 @@
       MDNode::get(Ctx, MDB.createConstant(ConstantInt::get(
                            Type::getInt32Ty(Ctx),
                            static_cast<uint32_t>(xxHash64(MangledType))))));
+  // If the module was compiled with -fpatchable-function-entry, ensure
+  // we use the same patchable-function-prefix.
+  if (auto *MD = mdconst::extract_or_null<ConstantInt>(
+          M.getModuleFlag("kcfi-offset"))) {
+    if (unsigned Offset = MD->getZExtValue())
+      F.addFnAttr("patchable-function-prefix", std::to_string(Offset));
+  }
 }
 
 FunctionCallee
Index: clang/test/CodeGen/kcfi.c
===================================================================
--- clang/test/CodeGen/kcfi.c
+++ clang/test/CodeGen/kcfi.c
@@ -1,5 +1,6 @@
 // RUN: %clang_cc1 -triple x86_64-unknown-linux-gnu -emit-llvm -fsanitize=kcfi -o - %s | FileCheck %s
 // RUN: %clang_cc1 -triple x86_64-unknown-linux-gnu -emit-llvm -fsanitize=kcfi -x c++ -o - %s | FileCheck %s
+// RUN: %clang_cc1 -triple x86_64-unknown-linux-gnu -emit-llvm -fsanitize=kcfi -fpatchable-function-entry-offset=3 -o - %s | FileCheck %s --check-prefixes=CHECK,OFFSET
 #if !__has_feature(kcfi)
 #error Missing kcfi?
 #endif
@@ -54,5 +55,6 @@
 }
 
 // CHECK-DAG: ![[#]] = !{i32 4, !"kcfi", i32 1}
+// OFFSET-DAG: ![[#]] = !{i32 4, !"kcfi-offset", i32 3}
 // CHECK-DAG: ![[#TYPE]] = !{i32 [[#HASH]]}
 // CHECK-DAG: ![[#TYPE2]] = !{i32 [[#%d,HASH2:]]}
Index: clang/lib/CodeGen/CodeGenModule.cpp
===================================================================
--- clang/lib/CodeGen/CodeGenModule.cpp
+++ clang/lib/CodeGen/CodeGenModule.cpp
@@ -758,8 +758,14 @@
                               CodeGenOpts.SanitizeCfiCanonicalJumpTables);
   }
 
-  if (LangOpts.Sanitize.has(SanitizerKind::KCFI))
+  if (LangOpts.Sanitize.has(SanitizerKind::KCFI)) {
     getModule().addModuleFlag(llvm::Module::Override, "kcfi", 1);
+    // KCFI assumes patchable-function-prefix is the same for all indirectly
+    // called functions. Store the expected offset for code generation.
+    if (CodeGenOpts.PatchableFunctionEntryOffset)
+      getModule().addModuleFlag(llvm::Module::Override, "kcfi-offset",
+                                CodeGenOpts.PatchableFunctionEntryOffset);
+  }
 
   if (CodeGenOpts.CFProtectionReturn &&
       Target.checkCFProtectionReturnSupported(getDiags())) {


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