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x86emul: fully ignore segment override for register-only operations
For ModRM encoded instructions with register operands we must not
overwrite ea.mem.seg (if a - bogus in that case - segment override was
present) as it aliases with ea.reg.
This is CVE-2015-2151 / XSA-123.
Reported-by: Felix Wilhelm <fwilhelm@ernw.de>
Signed-off-by: Jan Beulich <jbeulich@suse.com>
Reviewed-by: Tim Deegan <tim@xen.org>
Reviewed-by: Keir Fraser <keir@xen.org>
--- a/xen/arch/x86/x86_emulate/x86_emulate.c
+++ b/xen/arch/x86/x86_emulate/x86_emulate.c
@@ -1757,7 +1757,7 @@ x86_emulate(
}
}
- if ( override_seg != -1 )
+ if ( override_seg != -1 && ea.type == OP_MEM )
ea.mem.seg = override_seg;
/* Early operand adjustments. */
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