# HG changeset patch
# Parent 0ecb8ffe61b2ffff4331fcf49487c956ccb297a0
x86_emulate: Force #UD if lock prefix used with NOP instruction.

DTRACE uses 0xF0 0x90 0x90 0x90 0x90 (LOCK NOP NOP NOP NOP) to try and recieve a
#UD, but currently get GPF instead.

Fix x86_emulate, as #UD is the correct exception in this case.

Reported-by: Mukesh Rathor <mukesh.rathor@xxxxxxxxxx>
Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>

diff -r 0ecb8ffe61b2 xen/arch/x86/x86_emulate/x86_emulate.c
--- a/xen/arch/x86/x86_emulate/x86_emulate.c
+++ b/xen/arch/x86/x86_emulate/x86_emulate.c
@@ -2255,6 +2255,7 @@ x86_emulate(
         break;
 
     case 0x90: /* nop / xchg %%r8,%%rax */
+        generate_exception_if(lock_prefix, EXC_UD, -1);
         if ( !(rex_prefix & 1) )
             break; /* nop */