ajpaverd created this revision.
ajpaverd added reviewers: rnk, dmajor, pcc, hans.
Herald added subscribers: llvm-commits, cfe-commits, hiraditya.
Herald added projects: clang, LLVM.
Avoid using the `nocf_check` attribute with Control Flow Guard. Instead, use a
new `"guard_nocf"` function attribute to indicate that checks should not be
added on indirect calls within that function. Add support for
`__declspec(guard(nocf))` following the same syntax as MSVC.
Repository:
rG LLVM Github Monorepo
https://reviews.llvm.org/D72167
Files:
clang/include/clang/Basic/Attr.td
clang/include/clang/Basic/AttrDocs.td
clang/lib/CodeGen/CodeGenFunction.cpp
clang/lib/Sema/SemaDeclAttr.cpp
clang/test/CodeGen/guard_nocf.c
clang/test/CodeGenCXX/guard_nocf.cpp
llvm/docs/LangRef.rst
llvm/lib/Transforms/CFGuard/CFGuard.cpp
llvm/test/CodeGen/AArch64/cfguard-checks.ll
llvm/test/CodeGen/ARM/cfguard-checks.ll
llvm/test/CodeGen/X86/cfguard-checks.ll
Index: llvm/test/CodeGen/X86/cfguard-checks.ll
===================================================================
--- llvm/test/CodeGen/X86/cfguard-checks.ll
+++ llvm/test/CodeGen/X86/cfguard-checks.ll
@@ -8,8 +8,8 @@
declare i32 @target_func()
-; Test that Control Flow Guard checks are not added to functions with nocf_checks attribute.
-define i32 @func_nocf_checks() #0 {
+; Test that Control Flow Guard checks are not added to functions with the "guard_nocf" attribute.
+define i32 @func_guard_nocf() #0 {
entry:
%func_ptr = alloca i32 ()*, align 8
store i32 ()* @target_func, i32 ()** %func_ptr, align 8
@@ -17,17 +17,17 @@
%1 = call i32 %0()
ret i32 %1
- ; X32-LABEL: func_nocf_checks
+ ; X32-LABEL: func_guard_nocf
; X32: movl $_target_func, %eax
; X32-NOT: __guard_check_icall_fptr
; X32: calll *%eax
- ; X64-LABEL: func_nocf_checks
+ ; X64-LABEL: func_guard_nocf
; X64: leaq target_func(%rip), %rax
; X64-NOT: __guard_dispatch_icall_fptr
; X64: callq *%rax
}
-attributes #0 = { nocf_check }
+attributes #0 = { "guard_nocf" }
; Test that Control Flow Guard checks are added even at -O0.
Index: llvm/test/CodeGen/ARM/cfguard-checks.ll
===================================================================
--- llvm/test/CodeGen/ARM/cfguard-checks.ll
+++ llvm/test/CodeGen/ARM/cfguard-checks.ll
@@ -7,8 +7,8 @@
declare i32 @target_func()
-; Test that Control Flow Guard checks are not added to functions with nocf_checks attribute.
-define i32 @func_nocf_checks() #0 {
+; Test that Control Flow Guard checks are not added to functions with the "guard_nocf" attribute.
+define i32 @func_guard_nocf() #0 {
entry:
%func_ptr = alloca i32 ()*, align 8
store i32 ()* @target_func, i32 ()** %func_ptr, align 8
@@ -16,13 +16,13 @@
%1 = call arm_aapcs_vfpcc i32 %0()
ret i32 %1
- ; CHECK-LABEL: func_nocf_checks
+ ; CHECK-LABEL: func_guard_nocf
; CHECK: movw r0, :lower16:target_func
; CHECK: movt r0, :upper16:target_func
; CHECK-NOT: __guard_check_icall_fptr
; CHECK: blx r0
}
-attributes #0 = { nocf_check "target-cpu"="cortex-a9" "target-features"="+armv7-a,+dsp,+fp16,+neon,+strict-align,+thumb-mode,+vfp3"}
+attributes #0 = { "guard_nocf" "target-cpu"="cortex-a9" "target-features"="+armv7-a,+dsp,+fp16,+neon,+strict-align,+thumb-mode,+vfp3"}
; Test that Control Flow Guard checks are added even at -O0.
Index: llvm/test/CodeGen/AArch64/cfguard-checks.ll
===================================================================
--- llvm/test/CodeGen/AArch64/cfguard-checks.ll
+++ llvm/test/CodeGen/AArch64/cfguard-checks.ll
@@ -7,8 +7,8 @@
declare i32 @target_func()
-; Test that Control Flow Guard checks are not added to functions with nocf_checks attribute.
-define i32 @func_nocf_checks() #0 {
+; Test that Control Flow Guard checks are not added to functions with the "guard_nocf" attribute.
+define i32 @func_guard_nocf() #0 {
entry:
%func_ptr = alloca i32 ()*, align 8
store i32 ()* @target_func, i32 ()** %func_ptr, align 8
@@ -16,13 +16,13 @@
%1 = call i32 %0()
ret i32 %1
- ; CHECK-LABEL: func_nocf_checks
+ ; CHECK-LABEL: func_guard_nocf
; CHECK: adrp x8, target_func
; CHECK: add x8, x8, target_func
; CHECK-NOT: __guard_check_icall_fptr
; CHECK: blr x8
}
-attributes #0 = { nocf_check }
+attributes #0 = { "guard_nocf" }
; Test that Control Flow Guard checks are added even at -O0.
Index: llvm/lib/Transforms/CFGuard/CFGuard.cpp
===================================================================
--- llvm/lib/Transforms/CFGuard/CFGuard.cpp
+++ llvm/lib/Transforms/CFGuard/CFGuard.cpp
@@ -255,7 +255,7 @@
bool CFGuard::runOnFunction(Function &F) {
// Skip modules and functions for which CFGuard checks have been disabled.
- if (cfguard_module_flag != 2 || F.hasFnAttribute(Attribute::NoCfCheck))
+ if (cfguard_module_flag != 2 || F.hasFnAttribute("guard_nocf"))
return false;
SmallVector<CallBase *, 8> IndirectCalls;
@@ -277,7 +277,7 @@
// If no checks are needed, return early and add this attribute to indicate
// that subsequent CFGuard passes can skip this function.
if (IndirectCalls.empty()) {
- F.addFnAttr(Attribute::NoCfCheck);
+ F.addFnAttr("guard_nocf");
return false;
}
Index: llvm/docs/LangRef.rst
===================================================================
--- llvm/docs/LangRef.rst
+++ llvm/docs/LangRef.rst
@@ -1840,6 +1840,9 @@
the function. The instrumentation checks that the return address for the
function has not changed between the function prolog and eiplog. It is
currently x86_64-specific.
+``"guard_nocf"``
+ This attribute indicates that no Control Flow Guard checks will be added
+ within this function.
.. _glattrs:
Index: clang/test/CodeGenCXX/guard_nocf.cpp
===================================================================
--- /dev/null
+++ clang/test/CodeGenCXX/guard_nocf.cpp
@@ -0,0 +1,14 @@
+// RUN: %clang_cc1 -triple %ms_abi_triple -fms-extensions -emit-llvm -O0 -o - %s | FileCheck %s
+
+// The "guard_nocf" attribute should be added to this function
+__declspec(guard(nocf)) void Func_guard_nocf() {
+}
+
+// The "guard_nocf" attribute should not be added to this function.
+void Func_guard_cf() {
+}
+
+// CHECK: @{{.*}}Func_guard_nocf{{.*}}[[NOCF:#[0-9]+]]
+// CHECK: @{{.*}}Func_guard_cf{{.*}}[[CF:#[0-9]+]]
+// CHECK: attributes [[NOCF]] = { {{.*}}"guard_nocf"{{.*}} }
+// CHECK-NOT: attributes [[CF]] = { {{.*}}"guard_nocf"{{.*}} }
\ No newline at end of file
Index: clang/test/CodeGen/guard_nocf.c
===================================================================
--- /dev/null
+++ clang/test/CodeGen/guard_nocf.c
@@ -0,0 +1,14 @@
+// RUN: %clang_cc1 -triple %ms_abi_triple -fms-extensions -emit-llvm -O0 -o - %s | FileCheck %s
+
+// The "guard_nocf" attribute should be added to this function
+__declspec(guard(nocf)) void Func_guard_nocf() {
+}
+
+// The "guard_nocf" attribute should not be added to this function.
+void Func_guard_cf() {
+}
+
+// CHECK: @{{.*}}Func_guard_nocf{{.*}}[[NOCF:#[0-9]+]]
+// CHECK: @{{.*}}Func_guard_cf{{.*}}[[CF:#[0-9]+]]
+// CHECK: attributes [[NOCF]] = { {{.*}}"guard_nocf"{{.*}} }
+// CHECK-NOT: attributes [[CF]] = { {{.*}}"guard_nocf"{{.*}} }
\ No newline at end of file
Index: clang/lib/Sema/SemaDeclAttr.cpp
===================================================================
--- clang/lib/Sema/SemaDeclAttr.cpp
+++ clang/lib/Sema/SemaDeclAttr.cpp
@@ -6628,6 +6628,25 @@
D->addAttr(Attr::Create(S.Context, Argument, AL));
}
+static void handleCFGuardAttr(Sema &S, Decl *D, const ParsedAttr &AL) {
+ // The guard attribute takes a single argument.
+
+ if (!AL.isArgIdent(0)) {
+ S.Diag(AL.getLoc(), diag::err_attribute_argument_n_type)
+ << AL << 0 << AANT_ArgumentIdentifier;
+ return;
+ }
+
+ CFGuardAttr::GuardArg Arg;
+ IdentifierInfo *II = AL.getArgAsIdent(0)->Ident;
+ if (!CFGuardAttr::ConvertStrToGuardArg(II->getName(), Arg)) {
+ S.Diag(AL.getLoc(), diag::warn_attribute_type_not_supported) << AL << II;
+ return;
+ }
+
+ D->addAttr(::new (S.Context) CFGuardAttr(S.Context, AL, Arg));
+}
+
//===----------------------------------------------------------------------===//
// Top Level Sema Entry Points
//===----------------------------------------------------------------------===//
@@ -7256,6 +7275,9 @@
case ParsedAttr::AT_AbiTag:
handleAbiTagAttr(S, D, AL);
break;
+ case ParsedAttr::AT_CFGuard:
+ handleCFGuardAttr(S, D, AL);
+ break;
// Thread safety attributes:
case ParsedAttr::AT_AssertExclusiveLock:
Index: clang/lib/CodeGen/CodeGenFunction.cpp
===================================================================
--- clang/lib/CodeGen/CodeGenFunction.cpp
+++ clang/lib/CodeGen/CodeGenFunction.cpp
@@ -836,6 +836,12 @@
if (D && D->hasAttr<CFICanonicalJumpTableAttr>())
Fn->addFnAttr("cfi-canonical-jump-table");
+ if (D && D->hasAttr<CFGuardAttr>()) {
+ // Add the "guard_nocf" attribute to the function.
+ if (D->getAttr<CFGuardAttr>()->getGuard() == CFGuardAttr::GuardArg::nocf)
+ Fn->addFnAttr("guard_nocf");
+ }
+
if (getLangOpts().OpenCL) {
// Add metadata for a kernel function.
if (const FunctionDecl *FD = dyn_cast_or_null<FunctionDecl>(D))
Index: clang/include/clang/Basic/AttrDocs.td
===================================================================
--- clang/include/clang/Basic/AttrDocs.td
+++ clang/include/clang/Basic/AttrDocs.td
@@ -4558,6 +4558,27 @@
}];
}
+def CFGuardDocs : Documentation {
+ let Category = DocCatFunction;
+ let Content = [{
+Code can indicate CFG checks are not wanted with the ``__declspec(guard(nocf))``
+attribute. This directs the compiler to not insert any CFG checks for the entire
+function. This approach is typically used only sparingly in specific situations
+where the programmer has manually inserted "CFG-equivalent" protection. The
+programmer knows that they are calling through some read only function table
+whose address is obtained through read only memory references and for which the
+index is masked to the function table limit. This approach may also be applied
+to small wrapper functions that are not inlined and that do nothing more than
+make a call through a function pointer. Since incorrect usage of this directive
+can compromise the security of CFG, the programmer must be very careful using
+the directive. Typically, this usage is limited to very small functions that
+only call one function.
+
+`Control Flow Guard documentation <https://docs.microsoft.com/en-us/windows/win32/secbp/pe-metadata>`
+}];
+}
+
+
def HIPPinnedShadowDocs : Documentation {
let Category = DocCatType;
let Content = [{
Index: clang/include/clang/Basic/Attr.td
===================================================================
--- clang/include/clang/Basic/Attr.td
+++ clang/include/clang/Basic/Attr.td
@@ -2907,6 +2907,13 @@
let Documentation = [MSAllocatorDocs];
}
+def CFGuard : InheritableAttr {
+ let Spellings = [Declspec<"guard">];
+ let Subjects = SubjectList<[Function]>;
+ let Args = [EnumArgument<"Guard", "GuardArg", ["nocf"], ["nocf"]>];
+ let Documentation = [CFGuardDocs];
+}
+
def MSStruct : InheritableAttr {
let Spellings = [GCC<"ms_struct">];
let Subjects = SubjectList<[Record]>;
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