[clang] [PAuth] Use different discriminators for __int128_t / __uint128_t / _BitInt(n) (PR #140276)
Anton Korobeynikov via cfe-commits
cfe-commits at lists.llvm.org
Mon Jul 6 11:59:36 PDT 2026
https://github.com/asl updated https://github.com/llvm/llvm-project/pull/140276
>From ed3d47d43571d734aa01e9b6dbaa237f653374da Mon Sep 17 00:00:00 2001
From: Anton Korobeynikov <anton at korobeynikov.info>
Date: Fri, 16 May 2025 19:25:57 +0300
Subject: [PATCH 1/2] [PAuth] Use different discriminators for __int128_t /
__uint128_t / _BitInt(n) compared to other integer types when computing
function pointer type discriminator.
These parameter types have different parameter passing ABI as compared to
ordinary integer types (e.g. require 2 registers instead of 1) and therefore
this parameter passing difference could potentially be exploited should function
pointer is substituted.
---
clang/lib/AST/ASTContext.cpp | 14 ++++++---
.../ptrauth-function-type-discriminator.c | 31 +++++++++++++++++++
2 files changed, 41 insertions(+), 4 deletions(-)
diff --git a/clang/lib/AST/ASTContext.cpp b/clang/lib/AST/ASTContext.cpp
index a6eb87ab7d8aa..09d949b5e1643 100644
--- a/clang/lib/AST/ASTContext.cpp
+++ b/clang/lib/AST/ASTContext.cpp
@@ -3506,21 +3506,27 @@ static void encodeTypeForFunctionPointerAuth(const ASTContext &Ctx,
// Don't bother discriminating based on these types.
case Type::Pipe:
- case Type::BitInt:
case Type::ConstantMatrix:
OS << "?";
return;
+ case Type::BitInt: {
+ const auto *BtTy = T->castAs<BitIntType>();
+ OS << "D" << (BtTy->isUnsigned() ? "U" : "B") << BtTy->getNumBits() << "_";
+ return;
+ }
+
case Type::Builtin: {
const auto *BTy = T->castAs<BuiltinType>();
- switch (BTy->getKind()) {
+ const auto Kind = BTy->getKind();
+ switch (Kind) {
#define SIGNED_TYPE(Id, SingletonId) \
case BuiltinType::Id: \
- OS << "i"; \
+ OS << (Kind == BuiltinType::Int128 ? "n" : "i"); \
return;
#define UNSIGNED_TYPE(Id, SingletonId) \
case BuiltinType::Id: \
- OS << "i"; \
+ OS << (Kind == BuiltinType::UInt128 ? "o" : "i"); \
return;
#define PLACEHOLDER_TYPE(Id, SingletonId) case BuiltinType::Id:
#define BUILTIN_TYPE(Id, SingletonId)
diff --git a/clang/test/CodeGen/ptrauth-function-type-discriminator.c b/clang/test/CodeGen/ptrauth-function-type-discriminator.c
index 0952c1abf6c07..9bf4a8874c3c3 100644
--- a/clang/test/CodeGen/ptrauth-function-type-discriminator.c
+++ b/clang/test/CodeGen/ptrauth-function-type-discriminator.c
@@ -65,6 +65,37 @@ void (*fptr3)(void) = __builtin_ptrauth_sign_constant(&external_function, 2, 26)
// CHECK: @fptr4 = global ptr ptrauth (ptr @external_function, i32 2, i64 26, ptr @fptr4)
void (*fptr4)(void) = __builtin_ptrauth_sign_constant(&external_function, 2, __builtin_ptrauth_blend_discriminator(&fptr4, 26));
+extern void external_function_int(int);
+extern void external_function_char(char);
+extern void external_function_i128(__int128_t);
+extern void external_function_u128(__uint128_t);
+extern void external_function_b128(_BitInt(128));
+extern void external_function_b8(_BitInt(8));
+
+// Check discriminators of functions taking integer type arguments:
+
+// - Builtin integer types should be discriminated equally (so, pointer to
+// function taking int argument should accept function taking char argument
+// - _BitInt types are guaranteed distinct and therefore should be discriminated
+// differently
+// - __int128_t / __uint128_t are passed differently than char / int / long
+// (require two registers instead of one) and therefore should be discriminated
+// differently.
+
+// CHECK: @fptr5 = global ptr ptrauth (ptr @external_function_int, i32 0, i64 2712)
+// CHECK: @fptr6 = global ptr ptrauth (ptr @external_function_char, i32 0, i64 2712)
+void (*fptr5)(int) = external_function_int;
+void (*fptr6)(char) = external_function_char;
+
+// CHECK: @fptr7 = global ptr ptrauth (ptr @external_function_i128, i32 0, i64 23141)
+// CHECK: @fptr8 = global ptr ptrauth (ptr @external_function_u128, i32 0, i64 45743)
+// CHECK: @fptr9 = global ptr ptrauth (ptr @external_function_b128, i32 0, i64 17854)
+// CHECK: @fptr10 = global ptr ptrauth (ptr @external_function_b8, i32 0, i64 26383)
+void (*fptr7)(__int128_t) = external_function_i128;
+void (*fptr8)(__uint128_t) = external_function_u128;
+void (*fptr9)(_BitInt(128)) = external_function_b128;
+void (*fptr10)(_BitInt(8)) = external_function_b8;
+
// CHECK-LABEL: define{{.*}} void @test_call()
void test_call() {
// CHECK: [[T0:%.*]] = load ptr, ptr @fnptr,
>From 9034dfe720e13e94412ae9ac49c4c26da1f15c8f Mon Sep 17 00:00:00 2001
From: Anton Korobeynikov <anton at korobeynikov.info>
Date: Sun, 1 Jun 2025 23:55:32 -0700
Subject: [PATCH 2/2] Make type discrimination of 128-bit types optional
---
clang/include/clang/Basic/Features.def | 1 +
clang/include/clang/Basic/LangOptions.def | 2 ++
clang/include/clang/Options/Options.td | 2 ++
clang/lib/AST/ASTContext.cpp | 21 ++++++++++----
clang/lib/Driver/ToolChains/Clang.cpp | 3 ++
clang/lib/Frontend/CompilerInvocation.cpp | 4 +++
.../ptrauth-function-type-discriminator.c | 28 ++++++++++++-------
7 files changed, 45 insertions(+), 16 deletions(-)
diff --git a/clang/include/clang/Basic/Features.def b/clang/include/clang/Basic/Features.def
index f0a9c4889ea2d..aab2aaa18e5c2 100644
--- a/clang/include/clang/Basic/Features.def
+++ b/clang/include/clang/Basic/Features.def
@@ -164,6 +164,7 @@ FEATURE(ptrauth_indirect_gotos, LangOpts.PointerAuthIndirectGotos)
FEATURE(ptrauth_init_fini, LangOpts.PointerAuthInitFini)
FEATURE(ptrauth_init_fini_address_discrimination, LangOpts.PointerAuthInitFiniAddressDiscrimination)
FEATURE(ptrauth_elf_got, LangOpts.PointerAuthELFGOT)
+FEATURE(ptrauth_function_pointer_type_discrimination_128, LangOpts.PointerAuthFunctionTypeDiscrimination128)
FEATURE(ptrauth_objc_isa, LangOpts.PointerAuthObjcIsa)
FEATURE(ptrauth_objc_interface_sel, LangOpts.PointerAuthObjcInterfaceSel)
diff --git a/clang/include/clang/Basic/LangOptions.def b/clang/include/clang/Basic/LangOptions.def
index 1fb491a54a278..8ca0a0de50b56 100644
--- a/clang/include/clang/Basic/LangOptions.def
+++ b/clang/include/clang/Basic/LangOptions.def
@@ -129,6 +129,8 @@ LANGOPT(PointerAuthVTPtrTypeDiscrimination, 1, 0, NotCompatible, "incorporate ty
LANGOPT(PointerAuthTypeInfoVTPtrDiscrimination, 1, 0, NotCompatible, "incorporate type and address discrimination in authenticated vtable pointers for std::type_info")
LANGOPT(PointerAuthFunctionTypeDiscrimination, 1, 0, Benign,
"Use type discrimination when signing function pointers")
+LANGOPT(PointerAuthFunctionTypeDiscrimination128, 1, 0, NotCompatible,
+ "Use different discriminators for __int128_t / __uint128_t / _BitInt(n) compared to other integer types when computing function pointer type discriminator")
LANGOPT(PointerAuthInitFini, 1, 0, NotCompatible, "sign function pointers in init/fini arrays")
LANGOPT(PointerAuthInitFiniAddressDiscrimination, 1, 0, NotCompatible,
"incorporate address discrimination in authenticated function pointers in init/fini arrays")
diff --git a/clang/include/clang/Options/Options.td b/clang/include/clang/Options/Options.td
index b2e32c75e5745..e37ab43b89624 100644
--- a/clang/include/clang/Options/Options.td
+++ b/clang/include/clang/Options/Options.td
@@ -4995,6 +4995,8 @@ defm ptrauth_type_info_vtable_pointer_discrimination :
OptInCC1FFlag<"ptrauth-type-info-vtable-pointer-discrimination", "Enable type and address discrimination of vtable pointer of std::type_info">;
defm ptrauth_function_pointer_type_discrimination : OptInCC1FFlag<"ptrauth-function-pointer-type-discrimination",
"Enable type discrimination on C function pointers">;
+defm ptrauth_128bit_type_discrimination : OptInCC1FFlag<"ptrauth-128bit-type-discrimination",
+ "Do not use different discriminators for __int128_t / __uint128_t / _BitInt(n) compared to other integer types when computing function pointer type discriminator">;
defm ptrauth_indirect_gotos : OptInCC1FFlag<"ptrauth-indirect-gotos",
"Enable signing and authentication of indirect goto targets">;
defm ptrauth_init_fini : OptInCC1FFlag<"ptrauth-init-fini", "Enable signing of function pointers in init/fini arrays">;
diff --git a/clang/lib/AST/ASTContext.cpp b/clang/lib/AST/ASTContext.cpp
index 09d949b5e1643..1766a52197fb8 100644
--- a/clang/lib/AST/ASTContext.cpp
+++ b/clang/lib/AST/ASTContext.cpp
@@ -3510,11 +3510,14 @@ static void encodeTypeForFunctionPointerAuth(const ASTContext &Ctx,
OS << "?";
return;
- case Type::BitInt: {
- const auto *BtTy = T->castAs<BitIntType>();
- OS << "D" << (BtTy->isUnsigned() ? "U" : "B") << BtTy->getNumBits() << "_";
+ case Type::BitInt:
+ if (Ctx.getLangOpts().PointerAuthFunctionTypeDiscrimination128) {
+ const auto *BtTy = T->castAs<BitIntType>();
+ OS << "D" << (BtTy->isUnsigned() ? "U" : "B") << BtTy->getNumBits()
+ << "_";
+ } else
+ OS << "?";
return;
- }
case Type::Builtin: {
const auto *BTy = T->castAs<BuiltinType>();
@@ -3522,11 +3525,17 @@ static void encodeTypeForFunctionPointerAuth(const ASTContext &Ctx,
switch (Kind) {
#define SIGNED_TYPE(Id, SingletonId) \
case BuiltinType::Id: \
- OS << (Kind == BuiltinType::Int128 ? "n" : "i"); \
+ OS << (Kind == BuiltinType::Int128 && \
+ Ctx.getLangOpts().PointerAuthFunctionTypeDiscrimination128 \
+ ? "n" \
+ : "i"); \
return;
#define UNSIGNED_TYPE(Id, SingletonId) \
case BuiltinType::Id: \
- OS << (Kind == BuiltinType::UInt128 ? "o" : "i"); \
+ OS << (Kind == BuiltinType::UInt128 && \
+ Ctx.getLangOpts().PointerAuthFunctionTypeDiscrimination128 \
+ ? "o" \
+ : "i"); \
return;
#define PLACEHOLDER_TYPE(Id, SingletonId) case BuiltinType::Id:
#define BUILTIN_TYPE(Id, SingletonId)
diff --git a/clang/lib/Driver/ToolChains/Clang.cpp b/clang/lib/Driver/ToolChains/Clang.cpp
index a30b01a675b99..af073fc952631 100644
--- a/clang/lib/Driver/ToolChains/Clang.cpp
+++ b/clang/lib/Driver/ToolChains/Clang.cpp
@@ -1740,6 +1740,9 @@ void Clang::AddAArch64TargetArgs(const ArgList &Args,
options::OPT_fno_ptrauth_function_pointer_type_discrimination);
Args.addOptInFlag(CmdArgs, options::OPT_fptrauth_indirect_gotos,
options::OPT_fno_ptrauth_indirect_gotos);
+ Args.addOptInFlag(
+ CmdArgs, options::OPT_fptrauth_128bit_type_discrimination,
+ options::OPT_fno_ptrauth_128bit_type_discrimination);
}
if (Triple.isOSLinux() &&
Triple.getEnvironment() == llvm::Triple::PAuthTest) {
diff --git a/clang/lib/Frontend/CompilerInvocation.cpp b/clang/lib/Frontend/CompilerInvocation.cpp
index 6545307a8c8a7..14e52592f7824 100644
--- a/clang/lib/Frontend/CompilerInvocation.cpp
+++ b/clang/lib/Frontend/CompilerInvocation.cpp
@@ -3603,6 +3603,8 @@ static void GeneratePointerAuthArgs(const LangOptions &Opts,
GenerateArg(Consumer, OPT_fptrauth_type_info_vtable_pointer_discrimination);
if (Opts.PointerAuthFunctionTypeDiscrimination)
GenerateArg(Consumer, OPT_fptrauth_function_pointer_type_discrimination);
+ if (Opts.PointerAuthFunctionTypeDiscrimination128)
+ GenerateArg(Consumer, OPT_fptrauth_128bit_type_discrimination);
if (Opts.PointerAuthInitFini)
GenerateArg(Consumer, OPT_fptrauth_init_fini);
if (Opts.PointerAuthInitFiniAddressDiscrimination)
@@ -3636,6 +3638,8 @@ static void ParsePointerAuthArgs(LangOptions &Opts, ArgList &Args,
Args.hasArg(OPT_fptrauth_type_info_vtable_pointer_discrimination);
Opts.PointerAuthFunctionTypeDiscrimination =
Args.hasArg(OPT_fptrauth_function_pointer_type_discrimination);
+ Opts.PointerAuthFunctionTypeDiscrimination128 =
+ Args.hasArg(OPT_fptrauth_128bit_type_discrimination);
Opts.PointerAuthInitFini = Args.hasArg(OPT_fptrauth_init_fini);
Opts.PointerAuthInitFiniAddressDiscrimination =
Args.hasArg(OPT_fptrauth_init_fini_address_discrimination);
diff --git a/clang/test/CodeGen/ptrauth-function-type-discriminator.c b/clang/test/CodeGen/ptrauth-function-type-discriminator.c
index 9bf4a8874c3c3..280115862d927 100644
--- a/clang/test/CodeGen/ptrauth-function-type-discriminator.c
+++ b/clang/test/CodeGen/ptrauth-function-type-discriminator.c
@@ -1,18 +1,22 @@
// RUN: %clang_cc1 -fptrauth-function-pointer-type-discrimination -triple arm64e-apple-ios13 -fptrauth-calls -fptrauth-intrinsics \
-// RUN: -disable-llvm-passes -emit-llvm %s -o- | FileCheck --check-prefixes=CHECK,CHECKC %s
+// RUN: -disable-llvm-passes -emit-llvm %s -o- | FileCheck --check-prefixes=CHECK,CHECKC,CHECKNO128 %s
// RUN: %clang_cc1 -fptrauth-function-pointer-type-discrimination -triple arm64e-apple-ios13 -fptrauth-calls -fptrauth-intrinsics \
-// RUN: -disable-llvm-passes -emit-llvm -xc++ %s -o- | FileCheck --check-prefix=CHECK %s
+// RUN: -disable-llvm-passes -emit-llvm -xc++ %s -o- | FileCheck --check-prefixes=CHECK,CHECKNO128 %s
// RUN: %clang_cc1 -fptrauth-function-pointer-type-discrimination -triple arm64-apple-ios -fptrauth-calls -fptrauth-intrinsics -emit-pch %s -o %t.ast
// RUN: %clang_cc1 -fptrauth-function-pointer-type-discrimination -triple arm64-apple-ios -fptrauth-calls -fptrauth-intrinsics \
-// RUN: -emit-llvm -x ast -o - %t.ast | FileCheck --check-prefixes=CHECK,CHECKC %s
+// RUN: -emit-llvm -x ast -o - %t.ast | FileCheck --check-prefixes=CHECK,CHECKC,CHECKNO128 %s
+// RUN: %clang_cc1 -fptrauth-function-pointer-type-discrimination -triple arm64e-apple-ios13 -fptrauth-calls -fptrauth-intrinsics \
+// RUN: -fptrauth-128bit-type-discrimination -disable-llvm-passes -emit-llvm %s -o- | FileCheck --check-prefixes=CHECK,CHECKC,CHECK128 %s
// RUN: %clang_cc1 -fptrauth-function-pointer-type-discrimination -triple aarch64-linux-gnu -fptrauth-calls -fptrauth-intrinsics \
-// RUN: -disable-llvm-passes -emit-llvm %s -o- | FileCheck --check-prefixes=CHECK,CHECKC %s
+// RUN: -disable-llvm-passes -emit-llvm %s -o- | FileCheck --check-prefixes=CHECK,CHECKC,CHECKNO128 %s
// RUN: %clang_cc1 -fptrauth-function-pointer-type-discrimination -triple aarch64-linux-gnu -fptrauth-calls -fptrauth-intrinsics \
-// RUN: -disable-llvm-passes -emit-llvm -xc++ %s -o- | FileCheck --check-prefix=CHECK %s
+// RUN: -disable-llvm-passes -emit-llvm -xc++ %s -o- | FileCheck --check-prefixes=CHECK,CHECKNO128 %s
// RUN: %clang_cc1 -fptrauth-function-pointer-type-discrimination -triple aarch64-linux-gnu -fptrauth-calls -fptrauth-intrinsics -emit-pch %s -o %t.ast
// RUN: %clang_cc1 -fptrauth-function-pointer-type-discrimination -triple aarch64-linux-gnu -fptrauth-calls -fptrauth-intrinsics \
-// RUN: -emit-llvm -x ast -o - %t.ast | FileCheck --check-prefixes=CHECK,CHECKC %s
+// RUN: -emit-llvm -x ast -o - %t.ast | FileCheck --check-prefixes=CHECK,CHECKC,CHECKNO128 %s
+// RUN: %clang_cc1 -fptrauth-function-pointer-type-discrimination -triple aarch64-linux-gnu -fptrauth-calls -fptrauth-intrinsics \
+// RUN: -fptrauth-128bit-type-discrimination -disable-llvm-passes -emit-llvm %s -o- | FileCheck --check-prefixes=CHECK,CHECKC,CHECK128 %s
#ifdef __cplusplus
extern "C" {
@@ -87,10 +91,14 @@ extern void external_function_b8(_BitInt(8));
void (*fptr5)(int) = external_function_int;
void (*fptr6)(char) = external_function_char;
-// CHECK: @fptr7 = global ptr ptrauth (ptr @external_function_i128, i32 0, i64 23141)
-// CHECK: @fptr8 = global ptr ptrauth (ptr @external_function_u128, i32 0, i64 45743)
-// CHECK: @fptr9 = global ptr ptrauth (ptr @external_function_b128, i32 0, i64 17854)
-// CHECK: @fptr10 = global ptr ptrauth (ptr @external_function_b8, i32 0, i64 26383)
+// CHECK128: @fptr7 = global ptr ptrauth (ptr @external_function_i128, i32 0, i64 23141)
+// CHECK128: @fptr8 = global ptr ptrauth (ptr @external_function_u128, i32 0, i64 45743)
+// CHECK128: @fptr9 = global ptr ptrauth (ptr @external_function_b128, i32 0, i64 17854)
+// CHECK128: @fptr10 = global ptr ptrauth (ptr @external_function_b8, i32 0, i64 26383)
+// CHECKNO128: @fptr7 = global ptr ptrauth (ptr @external_function_i128, i32 0, i64 2712)
+// CHECKNO128: @fptr8 = global ptr ptrauth (ptr @external_function_u128, i32 0, i64 2712)
+// CHECKNO128: @fptr9 = global ptr ptrauth (ptr @external_function_b128, i32 0, i64 41228)
+// CHECKNO128: @fptr10 = global ptr ptrauth (ptr @external_function_b8, i32 0, i64 41228)
void (*fptr7)(__int128_t) = external_function_i128;
void (*fptr8)(__uint128_t) = external_function_u128;
void (*fptr9)(_BitInt(128)) = external_function_b128;
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