always save and restore %fs, %gs to ensure old segment entries are never

accessible to user from the hidden CPU segment registers.

always save and restore %fs, %gs to ensure old segment entries are never
c7317d4d · kolya · adcd16c3 · c7317d4d · c7317d4d
--- 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

--- 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;
 };