From b05299253fdd5a8a913f2799b7cdd2df040c8559 Mon Sep 17 00:00:00 2001
From: Gabe Black <gblack@eecs.umich.edu>
Date: Thu, 12 Jun 2008 00:51:50 -0400
Subject: [PATCH] X86: In non 64bit mode, throw a fault when a NULL segment is
 accessed.

---
 src/arch/x86/tlb.cc | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/src/arch/x86/tlb.cc b/src/arch/x86/tlb.cc
index f5e214a88..5d101a5ae 100644
--- a/src/arch/x86/tlb.cc
+++ b/src/arch/x86/tlb.cc
@@ -571,6 +571,9 @@ TLB::translate(RequestPtr &req, ThreadContext *tc, bool write, bool execute)
         // If we're not in 64-bit mode, do protection/limit checks
         if (!efer.lma || !csAttr.longMode) {
             DPRINTF(TLB, "Not in long mode. Checking segment protection.\n");
+            // Check for a NULL segment selector.
+            if (!tc->readMiscRegNoEffect(MISCREG_SEG_SEL(seg)))
+                return new GeneralProtection(0);
             SegAttr attr = tc->readMiscRegNoEffect(MISCREG_SEG_ATTR(seg));
             if (!attr.writable && write)
                 return new GeneralProtection(0);