https://github.com/ahmedbougacha created
https://github.com/llvm/llvm-project/pull/93903
This exposes the ABI-stable hash function that allows computing a 16-bit
discriminator from a constant string.
This allows manually matching the implicit string discriminators computed in
the ABI (e.g., from mangled names for vtable pointer/entry signing), as well as
enabling the use of interesting discriminators when manually annotating
specific pointers with the __ptrauth qualifier.
>From 61be7a922397d66773a8f4a6e476ea321f52f00c Mon Sep 17 00:00:00 2001
From: Ahmed Bougacha <ah...@bougacha.org>
Date: Thu, 30 May 2024 17:22:29 -0700
Subject: [PATCH] [clang] Define ptrauth_string_discriminator builtin.
This exposes the ABI-stable hash function that allows computing a 16-bit
discriminator from a constant string.
This allows manually matching the implicit string discriminators
computed in the ABI (e.g., from mangled names for vtable pointer/entry
signing), as well as enabling the use of interesting discriminators when
manually annotating specific pointers with the __ptrauth qualifier.
Co-Authored-By: John McCall <rjmcc...@apple.com>
---
clang/include/clang/Basic/Builtins.td | 6 ++++++
.../clang/Basic/DiagnosticSemaKinds.td | 2 ++
clang/lib/AST/ExprConstant.cpp | 7 +++++++
clang/lib/Headers/ptrauth.h | 17 ++++++++++++++++
clang/lib/Sema/SemaChecking.cpp | 20 +++++++++++++++++++
clang/test/CodeGen/ptrauth-intrinsics.c | 13 ++++++++++++
clang/test/Sema/ptrauth-intrinsics-macro.c | 5 +++++
7 files changed, 70 insertions(+)
diff --git a/clang/include/clang/Basic/Builtins.td
b/clang/include/clang/Basic/Builtins.td
index 11982af3fa609..836697632a3bc 100644
--- a/clang/include/clang/Basic/Builtins.td
+++ b/clang/include/clang/Basic/Builtins.td
@@ -4411,6 +4411,12 @@ def PtrauthAuth : Builtin {
let Prototype = "void*(void*,int,void*)";
}
+def PtrauthStringDiscriminator : Builtin {
+ let Spellings = ["__builtin_ptrauth_string_discriminator"];
+ let Attributes = [NoThrow, Const, Constexpr];
+ let Prototype = "size_t(char const*)";
+}
+
// OpenCL v2.0 s6.13.16, s9.17.3.5 - Pipe functions.
// We need the generic prototype, since the packet type could be anything.
def ReadPipe : OCLPipeLangBuiltin {
diff --git a/clang/include/clang/Basic/DiagnosticSemaKinds.td
b/clang/include/clang/Basic/DiagnosticSemaKinds.td
index f15cba63624ea..64add46248c69 100644
--- a/clang/include/clang/Basic/DiagnosticSemaKinds.td
+++ b/clang/include/clang/Basic/DiagnosticSemaKinds.td
@@ -928,6 +928,8 @@ def warn_ptrauth_sign_null_pointer :
def warn_ptrauth_auth_null_pointer :
Warning<"authenticating a null pointer will almost certainly trap">,
InGroup<PtrAuthNullPointers>;
+def err_ptrauth_string_not_literal : Error<
+ "argument must be a string literal%select{| of char type}0">;
/// main()
// static main() is not an error in C, just in C++.
diff --git a/clang/lib/AST/ExprConstant.cpp b/clang/lib/AST/ExprConstant.cpp
index f1aa19e4409e1..eafecfb5fe5b1 100644
--- a/clang/lib/AST/ExprConstant.cpp
+++ b/clang/lib/AST/ExprConstant.cpp
@@ -58,6 +58,7 @@
#include "llvm/ADT/StringExtras.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/SaveAndRestore.h"
+#include "llvm/Support/SipHash.h"
#include "llvm/Support/TimeProfiler.h"
#include "llvm/Support/raw_ostream.h"
#include <cstring>
@@ -12583,6 +12584,12 @@ bool IntExprEvaluator::VisitBuiltinCallExpr(const
CallExpr *E,
case Builtin::BI__builtin_expect_with_probability:
return Visit(E->getArg(0));
+ case Builtin::BI__builtin_ptrauth_string_discriminator: {
+ auto literal = cast<StringLiteral>(E->getArg(0)->IgnoreParenImpCasts());
+ auto result = getPointerAuthStableSipHash16(literal->getString());
+ return Success(result, E);
+ }
+
case Builtin::BI__builtin_ffs:
case Builtin::BI__builtin_ffsl:
case Builtin::BI__builtin_ffsll: {
diff --git a/clang/lib/Headers/ptrauth.h b/clang/lib/Headers/ptrauth.h
index 036665d75a91b..3e58af1802084 100644
--- a/clang/lib/Headers/ptrauth.h
+++ b/clang/lib/Headers/ptrauth.h
@@ -135,6 +135,17 @@ typedef __UINTPTR_TYPE__ ptrauth_generic_signature_t;
#define ptrauth_auth_data(__value, __old_key, __old_data)
\
__builtin_ptrauth_auth(__value, __old_key, __old_data)
+/* Compute a constant discriminator from the given string.
+
+ The result can be used as the second argument to
+ ptrauth_blend_discriminator or the third argument to the
+ __ptrauth qualifier. It has type size_t.
+
+ The argument must be a string literal.
+ A call to this function is an integer constant expression. */
+#define ptrauth_string_discriminator(__string)
\
+ __builtin_ptrauth_string_discriminator(__string)
+
/* Compute a signature for the given pair of pointer-sized values.
The order of the arguments is significant.
@@ -196,6 +207,12 @@ typedef __UINTPTR_TYPE__ ptrauth_generic_signature_t;
__value;
\
})
+#define ptrauth_string_discriminator(__string)
\
+ ({
\
+ (void)__string;
\
+ ((ptrauth_extra_data_t)0);
\
+ })
+
#define ptrauth_sign_generic_data(__value, __data)
\
({
\
(void)__value;
\
diff --git a/clang/lib/Sema/SemaChecking.cpp b/clang/lib/Sema/SemaChecking.cpp
index c3251f3cc9d81..f6012ef4b3601 100644
--- a/clang/lib/Sema/SemaChecking.cpp
+++ b/clang/lib/Sema/SemaChecking.cpp
@@ -2156,6 +2156,24 @@ static ExprResult PointerAuthAuthAndResign(Sema &S,
CallExpr *Call) {
return Call;
}
+static ExprResult PointerAuthStringDiscriminator(Sema &S, CallExpr *call) {
+ if (checkPointerAuthEnabled(S, call)) return ExprError();
+
+ // We've already performed normal call type-checking.
+ Expr *arg = call->getArgs()[0]->IgnoreParenImpCasts();
+
+ // Operand must be an ordinary or UTF-8 string literal.
+ auto literal = dyn_cast<StringLiteral>(arg);
+ if (!literal || literal->getCharByteWidth() != 1) {
+ S.Diag(arg->getExprLoc(), diag::err_ptrauth_string_not_literal)
+ << (literal ? 1 : 0)
+ << arg->getSourceRange();
+ return ExprError();
+ }
+
+ return call;
+}
+
static ExprResult BuiltinLaunder(Sema &S, CallExpr *TheCall) {
if (S.checkArgCount(TheCall, 1))
return ExprError();
@@ -2922,6 +2940,8 @@ Sema::CheckBuiltinFunctionCall(FunctionDecl *FDecl,
unsigned BuiltinID,
return PointerAuthSignGenericData(*this, TheCall);
case Builtin::BI__builtin_ptrauth_auth_and_resign:
return PointerAuthAuthAndResign(*this, TheCall);
+ case Builtin::BI__builtin_ptrauth_string_discriminator:
+ return PointerAuthStringDiscriminator(*this, TheCall);
// OpenCL v2.0, s6.13.16 - Pipe functions
case Builtin::BIread_pipe:
case Builtin::BIwrite_pipe:
diff --git a/clang/test/CodeGen/ptrauth-intrinsics.c
b/clang/test/CodeGen/ptrauth-intrinsics.c
index 17f28dddb3801..d602325da8b17 100644
--- a/clang/test/CodeGen/ptrauth-intrinsics.c
+++ b/clang/test/CodeGen/ptrauth-intrinsics.c
@@ -71,3 +71,16 @@ void test_sign_generic_data() {
// CHECK-NEXT: store i64 [[RESULT]], ptr @signature,
signature = __builtin_ptrauth_sign_generic_data(fnptr, ptr_discriminator);
}
+
+// CHECK-LABEL: define void @test_string_discriminator()
+void test_string_discriminator() {
+ // CHECK: [[X:%.*]] = alloca i32
+
+ // Check a couple of random discriminators used by Swift.
+
+ // CHECK: store i32 58298, ptr [[X]],
+ int x = __builtin_ptrauth_string_discriminator("InitializeWithCopy");
+
+ // CHECK: store i32 9112, ptr [[X]],
+ x = __builtin_ptrauth_string_discriminator("DestroyArray");
+}
diff --git a/clang/test/Sema/ptrauth-intrinsics-macro.c
b/clang/test/Sema/ptrauth-intrinsics-macro.c
index 07d6374045145..540f2846b7ce1 100644
--- a/clang/test/Sema/ptrauth-intrinsics-macro.c
+++ b/clang/test/Sema/ptrauth-intrinsics-macro.c
@@ -32,3 +32,8 @@ void test(int *dp, int value) {
int t2 = ptrauth_sign_generic_data(dp, 0);
(void)t2;
}
+
+void test_string_discriminator(int *dp) {
+ ptrauth_extra_data_t t0 = ptrauth_string_discriminator("string");
+ (void)t0;
+}
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