From b7dce29d9faf3597d009c853ed1fcbed9f7a7f68 Mon Sep 17 00:00:00 2001 From: Andrew Cooper Date: Thu, 5 Oct 2017 14:30:49 +0000 Subject: [PATCH] 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 Reviewed-by: Jan Beulich --- xen/arch/x86/x86_emulate/x86_emulate.c | 4 ++++ 1 file changed, 4 insertions(+) diff --git a/xen/arch/x86/x86_emulate/x86_emulate.c b/xen/arch/x86/x86_emulate/x86_emulate.c index d192280c4d..85383ea377 100644 --- a/xen/arch/x86/x86_emulate/x86_emulate.c +++ b/xen/arch/x86/x86_emulate/x86_emulate.c @@ -2505,6 +2505,10 @@ x86_decode( } done_prefixes: + /* %{e,c,s,d}s overrides are ignored in 64bit mode. */ + if ( mode_64bit() && override_seg < x86_seg_fs ) + override_seg = x86_seg_none; + if ( rex_prefix & REX_W ) op_bytes = 8; -- 2.39.5