[llvm] [PAC][InstCombine] Replace auth+sign with resign (PR #130807)

[via llvm-commits]

llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-llvm-transforms

Author: Anatoly Trosinenko (atrosinenko)

<details>
<summary>Changes</summary>

Prevent introducing signing oracles by increasing the chances that pointer resign pattern is detected and kept as a single operation until it is expanded in AsmPrinter.

With separate auth and sign intrinsics, it is possible that intermediate authenticated pointer is spilled to stack and reloaded before it is signed again, thus making it possible for the attacker to trick the `PAC*` instruction into signing an arbitrary pointer.

---
Full diff: https://github.com/llvm/llvm-project/pull/130807.diff


2 Files Affected:

- (modified) llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp (+23) 
- (modified) llvm/test/Transforms/InstCombine/ptrauth-intrinsics.ll (+58) 


``````````diff
diff --git a/llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp b/llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp
index 63f2fd0a733ce..a4b3c0afdb2f8 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp
@@ -2978,6 +2978,29 @@ Instruction *InstCombinerImpl::visitCallInst(CallInst &CI) {
         Intrinsic::getOrInsertDeclaration(II->getModule(), NewIntrin);
     return CallInst::Create(NewFn, CallArgs);
   }
+  case Intrinsic::ptrauth_sign: {
+    // auth + sign can be replaced with resign, which prevents unsafe
+    // spills and reloads of intermediate authenticated value.
+    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))
diff --git a/llvm/test/Transforms/InstCombine/ptrauth-intrinsics.ll b/llvm/test/Transforms/InstCombine/ptrauth-intrinsics.ll
index 208e162ac9416..15dd8bff19f2c 100644
--- a/llvm/test/Transforms/InstCombine/ptrauth-intrinsics.ll
+++ b/llvm/test/Transforms/InstCombine/ptrauth-intrinsics.ll
@@ -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)

``````````

</details>


https://github.com/llvm/llvm-project/pull/130807