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[PAC][InstCombine] Replace auth+sign with resign #130807

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[PAC][InstCombine] Replace auth+sign with resign #130807

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5e8621d
[PAC][InstCombine] Precommit tests for replacing auth+sign with resign
atrosinenko Mar 10, 2025
ede6389
[PAC][InstCombine] Replace auth+sign with resign
atrosinenko Mar 10, 2025
981ce94
Comment: explain the reason to combine auth+sign
atrosinenko Mar 15, 2025
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28 changes: 28 additions & 0 deletions llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -3024,6 +3024,34 @@ Instruction *InstCombinerImpl::visitCallInst(CallInst &CI) {
Intrinsic::getOrInsertDeclaration(II->getModule(), NewIntrin);
return CallInst::Create(NewFn, CallArgs);
}
case Intrinsic::ptrauth_sign: {
// Replace auth+sign with a single resign intrinsic.
// When auth and sign operations are performed separately, later compiler
// passes may spill intermediate result to memory as a raw, unprotected
// pointer, which makes it possible for an attacker to replace it under
// PAuth threat model. On the other hand, resign intrinsic is not expanded
// until AsmPrinter, when it is emitted as a contiguous, non-attackable
// sequence of instructions.
Value *Ptr = II->getArgOperand(0);
Value *SignKey = II->getArgOperand(1);
Value *SignDisc = II->getArgOperand(2);

const auto *CI = dyn_cast<CallBase>(Ptr);
if (!CI || CI->getIntrinsicID() != Intrinsic::ptrauth_auth)
break;

Value *BasePtr = CI->getOperand(0);
Value *AuthKey = CI->getArgOperand(1);
Value *AuthDisc = CI->getArgOperand(2);

// Not replacing auth+sign using the same schema with nop, as auth+sign
// pair traps on authentication failure.

Function *NewFn = Intrinsic::getOrInsertDeclaration(
II->getModule(), Intrinsic::ptrauth_resign);
return CallInst::Create(NewFn,
{BasePtr, AuthKey, AuthDisc, SignKey, SignDisc});
}
case Intrinsic::arm_neon_vtbl1:
case Intrinsic::aarch64_neon_tbl1:
if (Value *V = simplifyNeonTbl1(*II, Builder))
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58 changes: 58 additions & 0 deletions llvm/test/Transforms/InstCombine/ptrauth-intrinsics.ll
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Original file line number Diff line number Diff line change
Expand Up @@ -160,6 +160,64 @@ define i64 @test_ptrauth_resign_ptrauth_constant(ptr %p) {
ret i64 %authed
}

define i64 @test_ptrauth_auth_sign_same_schema(ptr %p) {
; CHECK-LABEL: @test_ptrauth_auth_sign_same_schema(
; CHECK-NEXT: [[P_INT:%.*]] = ptrtoint ptr [[P:%.*]] to i64
; CHECK-NEXT: [[RESIGNED:%.*]] = call i64 @llvm.ptrauth.resign(i64 [[P_INT]], i32 1, i64 1234, i32 1, i64 1234)
; CHECK-NEXT: ret i64 [[RESIGNED]]
;
%p.int = ptrtoint ptr %p to i64
%authed = call i64 @llvm.ptrauth.auth(i64 %p.int, i32 1, i64 1234)
%resigned = call i64 @llvm.ptrauth.sign(i64 %authed, i32 1, i64 1234)
ret i64 %resigned
}

define i64 @test_ptrauth_auth_sign_opaque_disc_same_schema(ptr %p, i64 %disc) {
; CHECK-LABEL: @test_ptrauth_auth_sign_opaque_disc_same_schema(
; CHECK-NEXT: [[P_INT:%.*]] = ptrtoint ptr [[P:%.*]] to i64
; CHECK-NEXT: [[RESIGNED:%.*]] = call i64 @llvm.ptrauth.resign(i64 [[P_INT]], i32 1, i64 [[DISC:%.*]], i32 1, i64 [[DISC]])
; CHECK-NEXT: ret i64 [[RESIGNED]]
;
%p.int = ptrtoint ptr %p to i64
%authed = call i64 @llvm.ptrauth.auth(i64 %p.int, i32 1, i64 %disc)
%resigned = call i64 @llvm.ptrauth.sign(i64 %authed, i32 1, i64 %disc)
ret i64 %resigned
}

define i64 @test_ptrauth_auth_sign_different_disc(ptr %p, i64 %disc) {
; CHECK-LABEL: @test_ptrauth_auth_sign_different_disc(
; CHECK-NEXT: [[P_INT:%.*]] = ptrtoint ptr [[P:%.*]] to i64
; CHECK-NEXT: [[RESIGNED:%.*]] = call i64 @llvm.ptrauth.resign(i64 [[P_INT]], i32 1, i64 [[DISC:%.*]], i32 1, i64 1234)
; CHECK-NEXT: ret i64 [[RESIGNED]]
;
%p.int = ptrtoint ptr %p to i64
%authed = call i64 @llvm.ptrauth.auth(i64 %p.int, i32 1, i64 %disc)
%resigned = call i64 @llvm.ptrauth.sign(i64 %authed, i32 1, i64 1234)
ret i64 %resigned
}

define i64 @test_ptrauth_auth_sign_different_key(ptr %p) {
; CHECK-LABEL: @test_ptrauth_auth_sign_different_key(
; CHECK-NEXT: [[P_INT:%.*]] = ptrtoint ptr [[P:%.*]] to i64
; CHECK-NEXT: [[RESIGNED:%.*]] = call i64 @llvm.ptrauth.resign(i64 [[P_INT]], i32 0, i64 1234, i32 1, i64 1234)
; CHECK-NEXT: ret i64 [[RESIGNED]]
;
%p.int = ptrtoint ptr %p to i64
%authed = call i64 @llvm.ptrauth.auth(i64 %p.int, i32 0, i64 1234)
%resigned = call i64 @llvm.ptrauth.sign(i64 %authed, i32 1, i64 1234)
ret i64 %resigned
}

define i64 @test_ptrauth_sign_nonauth_nonconst_disc(i64 %disc) {
; CHECK-LABEL: @test_ptrauth_sign_nonauth_nonconst_disc(
; CHECK-NEXT: [[SIGNED:%.*]] = call i64 @llvm.ptrauth.sign(i64 ptrtoint (ptr @foo to i64), i32 1, i64 [[DISC:%.*]])
; CHECK-NEXT: ret i64 [[SIGNED]]
;
%foo.int = ptrtoint ptr @foo to i64
%signed = call i64 @llvm.ptrauth.sign(i64 %foo.int, i32 1, i64 %disc)
ret i64 %signed
}

declare i64 @llvm.ptrauth.auth(i64, i32, i64)
declare i64 @llvm.ptrauth.sign(i64, i32, i64)
declare i64 @llvm.ptrauth.resign(i64, i32, i64, i32, i64)
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