From: Keir Fraser <keir.fraser@citrix.com>
Date: Fri, 25 Jul 2008 13:00:27 +0000 (+0100)
Subject: x86_emulate: fix unintended writeback on cmp/test instructions
X-Git-Tag: archive/raspbian/4.8.0-1+rpi1~1^2~14165^2~113
X-Git-Url: https://dgit.raspbian.org/%22http://www.example.com/cgi/success//%22http:/www.example.com/cgi/success/?a=commitdiff_plain;h=26c26ff17aabf675863b9882eee186fafbb5ff4e;p=xen.git

x86_emulate: fix unintended writeback on cmp/test instructions

This patch fixes an issue when x86_emulate is called with
force_writeback=1 set. It resulted in cmp and test instructions with
memory operands to have the mem value written back after instruction
emulation finished. This caused false alarms on writes to RO mem, and
might have caused other issues if unintended writes occured to device
registers in mmio space.

Signed-off-by: Trolle Selander <trolle.selander@eu.citrix.com>
---

diff --git a/xen/arch/x86/x86_emulate/x86_emulate.c b/xen/arch/x86/x86_emulate/x86_emulate.c
index 600705ff84..6fc1955783 100644
--- a/xen/arch/x86/x86_emulate/x86_emulate.c
+++ b/xen/arch/x86/x86_emulate/x86_emulate.c
@@ -1606,6 +1606,7 @@ x86_emulate(
         dst.val = _regs.eax;
     case 0x38 ... 0x3b: cmp: /* cmp */
         emulate_2op_SrcV("cmp", src, dst, _regs.eflags);
+        dst.type = OP_NONE;
         break;
 
     case 0x62: /* bound */ {
@@ -1707,6 +1708,7 @@ x86_emulate(
         dst.val = _regs.eax;
     case 0x84 ... 0x85: test: /* test */
         emulate_2op_SrcV("test", src, dst, _regs.eflags);
+        dst.type = OP_NONE;
         break;
 
     case 0x86 ... 0x87: xchg: /* xchg */