[Sandbox service resolver hooks] Remove the RET hijacking in ntdll.

sandbox/win/src/resolver_64.cc

Index: sandbox/win/src/resolver_64.cc
diff --git a/sandbox/win/src/resolver_64.cc b/sandbox/win/src/resolver_64.cc
index 8b2cc53c97cc58a3bcda0e492cc4c766243f614d..f1f135ea60eaf83e8829cbd18e2eb50f81ec1bbd 100644
--- a/sandbox/win/src/resolver_64.cc
+++ b/sandbox/win/src/resolver_64.cc
@@ -12,34 +12,25 @@
 
 namespace {
 
-const BYTE kPushRax = 0x50;
 const USHORT kMovRax = 0xB848;
-const ULONG kMovRspRax = 0x24048948;
-const BYTE kRetNp = 0xC3;
+const USHORT kJmpRax = 0xe0ff;
 
 #pragma pack(push, 1)
 struct InternalThunk {
   // This struct contains roughly the following code:
-  // 00 50                    push  rax
   // 01 48b8f0debc9a78563412  mov   rax,123456789ABCDEF0h
-  // 0b 48890424              mov   qword ptr [rsp],rax
-  // 0f c3                    ret
+  // ff e0                    jmp   rax
   //
-  // The code modifies rax, but that should not be an issue for the common
-  // calling conventions.
+  // The code modifies rax, but that's fine for x64 ABI.
 
   InternalThunk() {
-    push_rax = kPushRax;
     mov_rax = kMovRax;
+    jmp_rax = kJmpRax;
     interceptor_function = 0;
-    mov_rsp_rax = kMovRspRax;
-    ret = kRetNp;
   };
-  BYTE push_rax;        // = 50
   USHORT mov_rax;       // = 48 B8
   ULONG_PTR interceptor_function;
-  ULONG mov_rsp_rax;    // = 48 89 04 24
-  BYTE ret;             // = C3
+  USHORT jmp_rax;  // = ff e0
 };
 #pragma pack(pop)