From a58b713a5e32a8ca23f4e514aad65c8b0c1e8c30 Mon Sep 17 00:00:00 2001
From: Timo Kreuzer <timo.kreuzer@reactos.org>
Date: Sun, 10 Nov 2024 16:01:21 +0200
Subject: [PATCH] [UCRT] Properly implement __crt_fast_encode/decode_pointer

---
 sdk/lib/ucrt/inc/internal_shared.h | 14 ++++++++------
 1 file changed, 8 insertions(+), 6 deletions(-)

diff --git a/sdk/lib/ucrt/inc/internal_shared.h b/sdk/lib/ucrt/inc/internal_shared.h
index 08c1cb79463..7ad4b4bafe3 100644
--- a/sdk/lib/ucrt/inc/internal_shared.h
+++ b/sdk/lib/ucrt/inc/internal_shared.h
@@ -166,18 +166,20 @@ extern char __ImageBase;
 
 template<typename T>
 __forceinline
-T __crt_fast_encode_pointer(T Ptr)
+T __crt_fast_encode_pointer(T ptr)
 {
-    // FIXME: use cookie
-    return Ptr;
+    union { T Ptr; uintptr_t Uint; } u = { ptr };
+    u.Uint ^= __security_cookie;
+    return u.Ptr;
 }
 
 template<typename T>
 __forceinline
-T __crt_fast_decode_pointer(T Ptr)
+T __crt_fast_decode_pointer(T ptr)
 {
-    // FIXME: use cookie
-    return Ptr;
+    union { T Ptr; uintptr_t Uint; } u = { ptr };
+    u.Uint ^= __security_cookie;
+    return u.Ptr;
 }
 
 template<typename T>