From c7317d4dc74bcb1d0e939c6b06a724fce1510a4e Mon Sep 17 00:00:00 2001
From: kolya <kolya>
Date: Wed, 24 Sep 2008 01:48:31 +0000
Subject: [PATCH] always save and restore %fs, %gs to ensure old segment
 entries are never accessible to user from the hidden CPU segment registers.

---
 trapasm.S |  4 ++++
 x86.h     | 12 ++++++++----
 2 files changed, 12 insertions(+), 4 deletions(-)

diff --git a/trapasm.S b/trapasm.S
index acdca99..962ba10 100644
--- a/trapasm.S
+++ b/trapasm.S
@@ -8,6 +8,8 @@ alltraps:
   # Build trap frame.
   pushl %ds
   pushl %es
+  pushl %fs
+  pushl %gs
   pushal
   
   # Set up data segments.
@@ -24,6 +26,8 @@ alltraps:
 .globl trapret
 trapret:
   popal
+  popl %gs
+  popl %fs
   popl %es
   popl %ds
   addl $0x8, %esp  # trapno and errcode
diff --git a/x86.h b/x86.h
index 1f2c881..8db4dc9 100644
--- a/x86.h
+++ b/x86.h
@@ -135,21 +135,25 @@ struct trapframe {
   uint eax;
 
   // rest of trap frame
-  ushort es;
+  ushort gs;
   ushort padding1;
-  ushort ds;
+  ushort fs;
   ushort padding2;
+  ushort es;
+  ushort padding3;
+  ushort ds;
+  ushort padding4;
   uint trapno;
 
   // below here defined by x86 hardware
   uint err;
   uint eip;
   ushort cs;
-  ushort padding3;
+  ushort padding5;
   uint eflags;
 
   // below here only when crossing rings, such as from user to kernel
   uint esp;
   ushort ss;
-  ushort padding4;
+  ushort padding6;
 };