Re: [PATCH] arm64: KVM: VHE: save and restore some PSTATE bits

[gengdongjiu <gengdongjiu@huawei.com>]

On 2017/9/6 20:30, Vladimir Murzin wrote:
> On 06/09/17 13:14, gengdongjiu wrote:
>>
>>
>> On 2017/9/6 20:00, Vladimir Murzin wrote:
>>> On 06/09/17 11:35, gengdongjiu wrote:
>>>> Vladimir,
>>>>
>>>> On 2017/9/6 17:41, Vladimir Murzin wrote:
>>>>> Can you please elaborate on cases where PAN is not enabled?
>>>>
>>>> I mean the informal private usage, For example, he disabled the PAN dynamically to let kernel space to access the user space.
>>>> After he dynamic disabled the PAN, then switched to guest OS. after return to host. he found the PAN stage is modified.
>>>> Of cause this is not a formal usage, in our host kernel, it is always enabled, no dynamic change, but I means it may exist such cases.
>>>>
>>>>
>>>
>>> So, in short, there is no real issue with PAN, right? What about UAO?
>> For the PAN, if host OS dynamically enable/disable PAN should have issue.
>> Do you think that is not a issue as above description?
>>
>> "host OS dynamically disable the PAN, but after go back from the guest OS, The PAN is unexpectedly enabled"
> 
> Do you see effect of "PAN is unexpectedly enabled"?
In fact I did not encounter this case, but I think it can exist.
I think if host OS dynamically disable PAN, it wants the host kernel access the user space address space not through copy_to/from_user API.
Now if it is unexpectedly enabled, when host kernel still accesses the user space address,  it will happen MMU fault exception.


> 
> Cheers
> Vladimir
> 
>>
>>>
>>> Cheers
>>> Vladimir
>>>
>>> .
>>>
>>
>>
> 
> 
> .
>