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.coop...@citrix.com>
---
CC: Jan Beulich <jbeul...@suse.com>
I've got 3/4's of an XTF test for this, but not enough time to get it finished
in any reasable period. I noticed the issue originally when getting some
unexpected results from VMX_INSTRUCTION_INFO in some unrelated nested virt
work.
---
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 d192280..85383ea 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;
--
2.1.4
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