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List:       xen-devel
Subject:    Re: [Xen-devel] [PATCH v6 24/29] xen/x86: allow HVM guests to use hypercalls to bring up vCPUs
From:       "Jan Beulich" <JBeulich () suse ! com>
Date:       2015-09-30 15:41:09
Message-ID: 560C1EB502000078000A7349 () prv-mh ! provo ! novell ! com
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>>> On 30.09.15 at 16:23, <roger.pau@citrix.com> wrote:
> El 30/09/15 a les 14.35, Jan Beulich ha escrit:
>> On 30.09.15 at 14:19, <roger.pau@citrix.com> wrote:
>>> For VCPU_HVM_MODE_32B:
>>>  - rIP within CS limit.
>>>  - Check that CS.DPL == SS.DPL.
>>>  - rSP within SS limit.
>>>
>>> TBH I don't think we should enforce the last two checks, starting with
>>> an invalid stack should be fine as long as the user knows it. Maybe
>>> print a warning/debug message in this case?
>> 
>> I wouldn't check ESP at all. As to the two DPLs to, I don't think you
>> could launch a guest with these disagreeing.
> 
> I think we should basically check that the DPL of the CS segment is
> equal or greater than the DPL of all the other segments (ds, ss and es).

Except that for SS it needs to be equal.

Jan


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