File 5a856a2b-x86-emul-fix-64bit-decoding-of-segment-overrides.patch of Package xen.7317

# Commit b7dce29d9faf3597d009c853ed1fcbed9f7a7f68
# Date 2018-02-15 11:08:27 +0000
# Author Andrew Cooper <andrew.cooper3@citrix.com>
# Committer Andrew Cooper <andrew.cooper3@citrix.com>
x86/emul: Fix the decoding of segment overrides in 64bit mode

Explicit segment overides other than %fs and %gs are documented as ignored by
both Intel and AMD.

In practice, this means that:

 * Explicit uses of %ss don't actually yield #SS[0] for non-canonical
   memory references.
 * Explicit uses of %{e,c,d}s don't override %rbp/%rsp-based memory references
   to yield #GP[0] for non-canonical memory references.

Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>

--- a/xen/arch/x86/x86_emulate/x86_emulate.c
+++ b/xen/arch/x86/x86_emulate/x86_emulate.c
@@ -1527,6 +1527,10 @@ x86_emulate(
     }
  done_prefixes:
 
+    /* %{e,c,s,d}s overrides are ignored in 64bit mode. */
+    if ( mode_64bit() && (unsigned int)override_seg < x86_seg_fs )
+        override_seg = -1;
+
     if ( rex_prefix & REX_W )
         op_bytes = 8;