Re: [PATCH v12 1/9] x86: add generic resource (e.g. MSR) access hypercall

[George Dunlap <george.dunlap@eu.citrix.com>]

On 07/04/2014 11:52 AM, Andrew Cooper wrote:
> On 04/07/14 11:30, Jan Beulich wrote:
>>>>> On 04.07.14 at 11:40, <andrew.cooper3@citrix.com> wrote:
>>> On 04/07/14 09:34, Dongxiao Xu wrote:
>>>> Add a generic resource access hypercall for tool stack or other
>>>> components, e.g., accessing MSR, port I/O, etc.
>>>>
>>>> Signed-off-by: Dongxiao Xu <dongxiao.xu@intel.com>
>>> This still permits a user of the hypercalls to play with EFER or
>>> SYSENTER_EIP, which obviously is a very bad thing.
>>>
>>> There needs to be a whitelist of permitted MSRs which can be accessed.
>> Hmm, I'm not sure. One particular purpose I see here is to allow the
>> tool stack (or Dom0) access to MSRs Xen may not know about (yet).
>> Furthermore, this being a platform op, only the hardware domain
>> should ever have access, and it certainly ought to know what it's
>> doing. So the sum of these two considerations is: If at all, we may
>> want a black list here.
>>
>> Jan
>>
>
> I don't think it is safe for the toolstack to ever be playing with MSRs
> which Xen is completely unaware of.  There is no guarentee whatsoever
> that a new MSR which Xen is unaware of doesn't have security
> implications if the toolstack were to play with it.

But the toolstack is part of the trusted base; it should be thinking 
about the security implications as much as Xen should.

  -George