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

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Message-ID: <11e22405-1214-3dee-e2d2-f1e10340d0e4@huawei.com>
Date:   Wed, 6 Sep 2017 20:44:54 +0800
From:   gengdongjiu <gengdongjiu@...wei.com>
To:     Vladimir Murzin <vladimir.murzin@....com>,
        Marc Zyngier <marc.zyngier@....com>,
        "christoffer.dall@...aro.org" <christoffer.dall@...aro.org>,
        "pbonzini@...hat.com" <pbonzini@...hat.com>,
        "rkrcmar@...hat.com" <rkrcmar@...hat.com>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "kvmarm@...ts.cs.columbia.edu" <kvmarm@...ts.cs.columbia.edu>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "suzuki.poulose@....com" <suzuki.poulose@....com>,
        <mark.rutland@....com>, <catalin.marinas@....com>
CC:     James Morse <James.Morse@....com>, <zhanghaibin7@...wei.com>,
        Huangshaoyu <huangshaoyu@...wei.com>
Subject: Re: [PATCH] arm64: KVM: VHE: save and restore some PSTATE bits



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
>>>
>>> .
>>>
>>
>>
> 
> 
> .
>