[CFI] Fix Direct Call Issues in CFI Dispatch Table (llvm#69663)

I discovered two issues for when a CFI dispatch table entry is used as a direct call. # Inlining There is the possibility that the dispatch table entry contains only a single function pointer: ``` ; Function Attrs: naked nocf_check define private void @.cfi.jumptable() #6 align 8 { entry: call void asm sideeffect "jmp ${0:c}@plt\0Aint3\0Aint3\0Aint3\0A", "s"(ptr @_Z7throw_ei) unreachable } ``` If this function is inlined, the unreachable follows and ruins the containing function. # Exception Handling The dispatch table is always marked NoUnwind. This is fine if the entries are never used directly, but if a direct call is used which the containing function expects to throw, it will no longer throw and the exception handling code will be lost.
Ericsson · Dec 6, 2023 · 81360ec · 81360ec
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Showing 8 changed files with 446 additions and 24 deletions.
diff --git a/llvm/lib/Transforms/IPO/LowerTypeTests.cpp b/llvm/lib/Transforms/IPO/LowerTypeTests.cpp
@@ -1467,9 +1467,19 @@ void LowerTypeTestsModule::createJumpTable(
   SmallVector<Value *, 16> AsmArgs;
   AsmArgs.reserve(Functions.size() * 2);
 
-  for (GlobalTypeMember *GTM : Functions)
+  // Check if all entries have the NoUnwind attribute.
+  // If all entries have it, we can safely mark the
+  // cfi.jumptable as NoUnwind, otherwise, direct calls
+  // to the jump table will not handle exceptions properly
+  bool areAllEntriesNounwind = true;
+  for (GlobalTypeMember *GTM : Functions) {
+    if (!llvm::cast<llvm::Function>(GTM->getGlobal())
+             ->hasFnAttribute(llvm::Attribute::NoUnwind)) {
+      areAllEntriesNounwind = false;
+    }
     createJumpTableEntry(AsmOS, ConstraintOS, JumpTableArch, AsmArgs,
                          cast<Function>(GTM->getGlobal()));
+  }
 
   // Align the whole table by entry size.
   F->setAlignment(Align(getJumpTableEntrySize()));
@@ -1512,8 +1522,13 @@ void LowerTypeTestsModule::createJumpTable(
   // -fcf-protection=.
   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);
+
+  // Make sure we don't emit .eh_frame for this function if it isn't needed.
+  if (areAllEntriesNounwind)
+    F->addFnAttr(Attribute::NoUnwind);
+
+  // Make sure we do not inline any calls to the cfi.jumptable.
+  F->addFnAttr(Attribute::NoInline);
 
   BasicBlock *BB = BasicBlock::Create(M.getContext(), "entry", F);
   IRBuilder<> IRB(BB);

diff --git a/llvm/test/Transforms/LowerTypeTests/aarch64-jumptable.ll b/llvm/test/Transforms/LowerTypeTests/aarch64-jumptable.ll
@@ -1,3 +1,4 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --check-attributes --include-generated-funcs --version 2
 ; RUN: opt -S -passes=lowertypetests -mtriple=aarch64-unknown-linux-gnu %s | FileCheck --check-prefixes=AARCH64 %s
 
 ; Test for the jump table generation with branch protection on AArch64
@@ -6,7 +7,6 @@ target datalayout = "e-p:64:64"
 
 @0 = private unnamed_addr constant [2 x ptr] [ptr @f, ptr @g], align 16
 
-; AARCH64: @f = alias void (), ptr @[[JT:.*]]
 
 define void @f() !type !0 {
   ret void
@@ -29,11 +29,30 @@ define i1 @foo(ptr %p) {
 
 !1 = !{i32 4, !"branch-target-enforcement", i32 1}
 
-; AARCH64:   define private void @[[JT]]() #[[ATTR:.*]] align 8 {
 
-; AARCH64:      bti c
-; AARCH64-SAME: b $0
-; AARCH64-SAME: bti c
-; AARCH64-SAME: b $1
-
-; AARCH64: attributes #[[ATTR]] = { naked nounwind "branch-target-enforcement"="false" "sign-return-address"="none"
+; AARCH64-LABEL: define hidden void @f.cfi() !type !1 {
+; AARCH64-NEXT:    ret void
+;
+;
+; AARCH64-LABEL: define internal void @g.cfi() !type !1 {
+; AARCH64-NEXT:    ret void
+;
+;
+; AARCH64-LABEL: define i1 @foo
+; AARCH64-SAME: (ptr [[P:%.*]]) {
+; AARCH64-NEXT:    [[TMP1:%.*]] = ptrtoint ptr [[P]] to i64
+; AARCH64-NEXT:    [[TMP2:%.*]] = sub i64 [[TMP1]], ptrtoint (ptr @.cfi.jumptable to i64)
+; AARCH64-NEXT:    [[TMP3:%.*]] = lshr i64 [[TMP2]], 3
+; AARCH64-NEXT:    [[TMP4:%.*]] = shl i64 [[TMP2]], 61
+; AARCH64-NEXT:    [[TMP5:%.*]] = or i64 [[TMP3]], [[TMP4]]
+; AARCH64-NEXT:    [[TMP6:%.*]] = icmp ule i64 [[TMP5]], 1
+; AARCH64-NEXT:    ret i1 [[TMP6]]
+;
+;
+; AARCH64: Function Attrs: naked noinline
+; AARCH64-LABEL: define private void @.cfi.jumptable
+; AARCH64-SAME: () #[[ATTR1:[0-9]+]] align 8 {
+; AARCH64-NEXT:  entry:
+; AARCH64-NEXT:    call void asm sideeffect "bti c\0Ab $0\0Abti c\0Ab $1\0A", "s,s"(ptr @f.cfi, ptr @g.cfi)
+; AARCH64-NEXT:    unreachable
+;
diff --git a/llvm/test/Transforms/LowerTypeTests/cfi-nounwind-direct-call.ll b/llvm/test/Transforms/LowerTypeTests/cfi-nounwind-direct-call.ll
@@ -0,0 +1,160 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --check-attributes --include-generated-funcs --version 2
+; RUN: opt < %s -passes='lowertypetests,default<O3>' -S | FileCheck %s
+
+; This IR is based of the following C++
+; which was compiled with:
+; clang -cc1 -fexceptions -fcxx-exceptions \
+; -std=c++11 -internal-isystem llvm-project/build/lib/clang/17/include \
+; -nostdsysteminc -triple x86_64-unknown-linux -fsanitize=cfi-icall \
+; -fsanitize-cfi-cross-dso -fsanitize-trap=cfi-icall -Oz -S -emit-llvm
+; int (*catch_ptr)(int);
+; int nothrow_e (int num) noexcept {
+;   if (num) return 1;
+;   return 0;
+; }
+; int call_catch(int num) {
+;   catch_ptr = &nothrow_e;
+;   return catch_ptr(num);
+; }
+
+target datalayout = "e-m:e-p270:32:32-p271:32:32-p272:64:64-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-unknown-linux"
+
+@catch_ptr = local_unnamed_addr global ptr null, align 8
+@llvm.used = appending global [1 x ptr] [ptr @__cfi_check_fail], section "llvm.metadata"
+
+; Function Attrs: minsize mustprogress nofree norecurse nosync nounwind optsize willreturn memory(none)
+define dso_local noundef i32 @_Z9nothrow_ei(i32 noundef %num) #0 !type !4 !type !5 !type !6 {
+entry:
+  %tobool.not = icmp ne i32 %num, 0
+  %. = zext i1 %tobool.not to i32
+  ret i32 %.
+}
+
+; Function Attrs: minsize mustprogress nounwind optsize
+define dso_local noundef i32 @_Z10call_catchi(i32 noundef %num) local_unnamed_addr #1 !type !4 !type !5 !type !6 {
+entry:
+  store ptr @_Z9nothrow_ei, ptr @catch_ptr, align 8, !tbaa !7
+  %0 = tail call i1 @llvm.type.test(ptr nonnull @_Z9nothrow_ei, metadata !"_ZTSFiiE"), !nosanitize !11
+  br i1 %0, label %cfi.cont, label %cfi.slowpath, !prof !12, !nosanitize !11
+
+cfi.slowpath:                                     ; preds = %entry
+  tail call void @__cfi_slowpath(i64 5174074510188755522, ptr nonnull @_Z9nothrow_ei) #5, !nosanitize !11
+  br label %cfi.cont, !nosanitize !11
+
+cfi.cont:                                         ; preds = %cfi.slowpath, %entry
+  %tobool.not.i = icmp ne i32 %num, 0
+  %..i = zext i1 %tobool.not.i to i32
+  ret i32 %..i
+}
+
+; Function Attrs: mustprogress nocallback nofree nosync nounwind speculatable willreturn memory(none)
+declare i1 @llvm.type.test(ptr, metadata) #2
+
+declare void @__cfi_slowpath(i64, ptr) local_unnamed_addr
+
+; Function Attrs: minsize optsize
+define weak_odr hidden void @__cfi_check_fail(ptr noundef %0, ptr noundef %1) #3 {
+entry:
+  %.not = icmp eq ptr %0, null, !nosanitize !11
+  br i1 %.not, label %trap, label %cont, !nosanitize !11
+
+trap:                                             ; preds = %cont, %entry
+  tail call void @llvm.ubsantrap(i8 2) #6, !nosanitize !11
+  unreachable, !nosanitize !11
+
+cont:                                             ; preds = %entry
+  %2 = load i8, ptr %0, align 4, !nosanitize !11
+  %switch = icmp ult i8 %2, 5
+  br i1 %switch, label %trap, label %cont6
+
+cont6:                                            ; preds = %cont
+  ret void, !nosanitize !11
+}
+
+; Function Attrs: cold noreturn nounwind
+declare void @llvm.ubsantrap(i8 immarg) #4
+
+define weak void @__cfi_check(i64 %0, ptr %1, ptr %2) local_unnamed_addr {
+entry:
+  tail call void @llvm.trap()
+  unreachable
+}
+
+; Function Attrs: cold noreturn nounwind
+declare void @llvm.trap() #4
+
+attributes #0 = { minsize mustprogress nofree norecurse nosync nounwind optsize willreturn memory(none) "min-legal-vector-width"="0" "no-trapping-math"="true" "stack-protector-buffer-size"="8" "target-features"="+cx8,+mmx,+sse,+sse2,+x87" }
+attributes #1 = { minsize mustprogress nounwind optsize "min-legal-vector-width"="0" "no-trapping-math"="true" "stack-protector-buffer-size"="8" "target-features"="+cx8,+mmx,+sse,+sse2,+x87" }
+attributes #2 = { mustprogress nocallback nofree nosync nounwind speculatable willreturn memory(none) }
+attributes #3 = { minsize optsize "min-legal-vector-width"="0" "no-trapping-math"="true" "stack-protector-buffer-size"="8" "target-features"="+cx8,+mmx,+sse,+sse2,+x87" }
+attributes #4 = { cold noreturn nounwind }
+attributes #5 = { nounwind }
+attributes #6 = { noreturn nounwind }
+
+!llvm.module.flags = !{!0, !1, !2}
+!llvm.ident = !{!3}
+
+!0 = !{i32 1, !"wchar_size", i32 4}
+!1 = !{i32 4, !"Cross-DSO CFI", i32 1}
+!2 = !{i32 4, !"CFI Canonical Jump Tables", i32 0}
+!3 = !{!"clang version 17.0.2"}
+!4 = !{i64 0, !"_ZTSFiiE"}
+!5 = !{i64 0, !"_ZTSFiiE.generalized"}
+!6 = !{i64 0, i64 5174074510188755522}
+!7 = !{!8, !8, i64 0}
+!8 = !{!"any pointer", !9, i64 0}
+!9 = !{!"omnipotent char", !10, i64 0}
+!10 = !{!"Simple C++ TBAA"}
+!11 = !{}
+!12 = !{!"branch_weights", i32 1048575, i32 1}
+; CHECK: Function Attrs: minsize mustprogress nofree norecurse nosync nounwind optsize willreturn memory(none)
+; CHECK-LABEL: define dso_local noundef i32 @_Z9nothrow_ei
+; CHECK-SAME: (i32 noundef [[NUM:%.*]]) #[[ATTR0:[0-9]+]] !type !4 !type !5 !type !6 {
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    [[TOBOOL_NOT:%.*]] = icmp ne i32 [[NUM]], 0
+; CHECK-NEXT:    [[DOT:%.*]] = zext i1 [[TOBOOL_NOT]] to i32
+; CHECK-NEXT:    ret i32 [[DOT]]
+;
+;
+; CHECK: Function Attrs: minsize mustprogress nofree norecurse nosync nounwind optsize willreturn memory(write, argmem: none, inaccessiblemem: none)
+; CHECK-LABEL: define dso_local noundef i32 @_Z10call_catchi
+; CHECK-SAME: (i32 noundef [[NUM:%.*]]) local_unnamed_addr #[[ATTR1:[0-9]+]] !type !4 !type !5 !type !6 {
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    store ptr @_Z9nothrow_ei.cfi_jt, ptr @catch_ptr, align 8, !tbaa [[TBAA7:![0-9]+]]
+; CHECK-NEXT:    [[TOBOOL_NOT_I:%.*]] = icmp ne i32 [[NUM]], 0
+; CHECK-NEXT:    [[DOT_I:%.*]] = zext i1 [[TOBOOL_NOT_I]] to i32
+; CHECK-NEXT:    ret i32 [[DOT_I]]
+;
+;
+; CHECK: Function Attrs: minsize optsize
+; CHECK-LABEL: define weak_odr hidden void @__cfi_check_fail
+; CHECK-SAME: (ptr noundef [[TMP0:%.*]], ptr noundef [[TMP1:%.*]]) #[[ATTR2:[0-9]+]] {
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    [[DOTNOT:%.*]] = icmp eq ptr [[TMP0]], null, !nosanitize !11
+; CHECK-NEXT:    br i1 [[DOTNOT]], label [[TRAP:%.*]], label [[CONT:%.*]], !nosanitize !11
+; CHECK:       trap:
+; CHECK-NEXT:    tail call void @llvm.ubsantrap(i8 2) #[[ATTR5:[0-9]+]], !nosanitize !11
+; CHECK-NEXT:    unreachable, !nosanitize !11
+; CHECK:       cont:
+; CHECK-NEXT:    [[TMP2:%.*]] = load i8, ptr [[TMP0]], align 4, !nosanitize !11
+; CHECK-NEXT:    [[SWITCH:%.*]] = icmp ult i8 [[TMP2]], 5
+; CHECK-NEXT:    br i1 [[SWITCH]], label [[TRAP]], label [[CONT6:%.*]]
+; CHECK:       cont6:
+; CHECK-NEXT:    ret void, !nosanitize !11
+;
+;
+; CHECK-LABEL: define weak void @__cfi_check
+; CHECK-SAME: (i64 [[TMP0:%.*]], ptr [[TMP1:%.*]], ptr [[TMP2:%.*]]) local_unnamed_addr {
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    tail call void @llvm.trap()
+; CHECK-NEXT:    unreachable
+;
+;
+; CHECK: Function Attrs: naked nocf_check noinline nounwind
+; CHECK-LABEL: define internal void @_Z9nothrow_ei.cfi_jt
+; CHECK-SAME: () #[[ATTR4:[0-9]+]] align 8 {
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    tail call void asm sideeffect "jmp ${0:c}@plt\0Aint3\0Aint3\0Aint3\0A", "s"(ptr nonnull @_Z9nothrow_ei) #[[ATTR6:[0-9]+]]
+; CHECK-NEXT:    unreachable
+;