[RFC PATCH v2 0/3] Add segment limit checks to emulator

[Mohammed Gamal <m.gamal005@gmail.com>]

After some conversation with Avi concerning why unreal mode has been seen to work
with KVM on Intel. It clears out the scenario is caused as follows:

- guest enters big real mode
- kvm squashes limit to 64k-1
- guest executes instructions with offset > 64k
- cpu issues #GP due to limit violation
- kvm handle_rmode_exception() -> emulator
- emulator ignores limit, emulates instruction

With these applied I am getting vmentry failures with SeaBIOS and
gPXE. I could still get SeaBIOS to work with emulate_invalid_guest_state=1.
So it's needless to say that these patches are not meant for merging!

--------

Changes from v1:
- Added seg_override_limit() and emulate_ss() helpers in emulator
- Corrected limit check return values for long mode
- Limit Checking is now consistent with the Intel documentation

--------

Mohammed Gamal (3):
  Add helper methods to get segment limits
  x86 emulator: Add cs_base() helper
  x86 emulator: Add segment limit checks and helper functions

 arch/x86/include/asm/kvm_emulate.h |    1 +
 arch/x86/include/asm/kvm_host.h    |    1 +
 arch/x86/kvm/emulate.c             |  143 ++++++++++++++++++++++++++++++------
 arch/x86/kvm/svm.c                 |    8 ++
 arch/x86/kvm/vmx.c                 |    8 ++
 arch/x86/kvm/x86.c                 |   12 +++
 6 files changed, 150 insertions(+), 23 deletions(-)