[PATCH 0/2] MR721: Draft: ntoskrnl: Implement cmp instruction with opcode 0x83

[Etaash Mathamsetty (＠etaash.mathamsetty)]

required for vgk.sys (vanguard anti-cheat)

[PATCH 1/2] implement cmp instruction

[Etaash Mathamsetty]

From: Etaash Mathamsetty

---
 dlls/ntoskrnl.exe/instr.c | 22 ++++++++++++++++++++++
 1 file changed, 22 insertions(+)

diff --git a/dlls/ntoskrnl.exe/instr.c b/dlls/ntoskrnl.exe/instr.c
index 8f1aa4d45a3..fe559496004 100644
--- a/dlls/ntoskrnl.exe/instr.c
+++ b/dlls/ntoskrnl.exe/instr.c
@@ -890,7 +890,29 @@ static DWORD emulate_instruction( EXCEPTION_RECORD *rec, CONTEXT *context )
         }
         break;  /* Unable to emulate it */
     }
+    case 0x83: /* cmp r/m imm8 */
+    {
+        BYTE* data = INSTR_GetOperandAddr(context, instr + 1, prefixlen + 1, long_addr, rex, segprefix, &len);
+        SIZE_T offset = data - user_shared_data;
+        SIZE_T data_size = get_op_size(long_op, rex);
+        if(offset <= KSHARED_USER_DATA_PAGE_SIZE - data_size)
+        {
+            TRACE("USD offset %#x at %p\n", (unsigned int)offset, (void*)context->Rip);
+
+            /* Clear ZF and CF */
+            context->EFlags &= ~(1UL << 6);
+            context->EFlags &= ~(1UL);
+
+            if(*(wine_user_shared_data + offset) == instr[2])
+                context->EFlags |= (1UL << 6); /* ZF */
+            else if(*(wine_user_shared_data + offset) < instr[2])
+                context->EFlags |= (1UL); /* CF */

+            context->Rip += prefixlen + len + 2;
+            return ExceptionContinueExecution;
+        }
+        break;
+    }
     case 0xa0: /* mov Ob, AL */
     case 0xa1: /* mov Ovqp, rAX */
     {

[PATCH 2/2] fix minor styling

[Etaash Mathamsetty]

From: Etaash Mathamsetty

---
 dlls/ntoskrnl.exe/instr.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/dlls/ntoskrnl.exe/instr.c b/dlls/ntoskrnl.exe/instr.c
index fe559496004..cb3cce521c9 100644
--- a/dlls/ntoskrnl.exe/instr.c
+++ b/dlls/ntoskrnl.exe/instr.c
@@ -892,7 +892,7 @@ static DWORD emulate_instruction( EXCEPTION_RECORD *rec, CONTEXT *context )
     }
     case 0x83: /* cmp r/m imm8 */
     {
-        BYTE* data = INSTR_GetOperandAddr(context, instr + 1, prefixlen + 1, long_addr, rex, segprefix, &len);
+        BYTE *data = INSTR_GetOperandAddr(context, instr + 1, prefixlen + 1, long_addr, rex, segprefix, &len);
         SIZE_T offset = data - user_shared_data;
         SIZE_T data_size = get_op_size(long_op, rex);
         if(offset <= KSHARED_USER_DATA_PAGE_SIZE - data_size)