Re: [PATCH] arm64: KVM: VHE: reset PSTATE.UAO when switch to host

[Marc Zyngier]

On 07/09/17 11:05, gengdongjiu wrote:
> Hi James,
> 
> On 2017/9/7 17:20, James Morse wrote:
>> Hi Dongjiu Geng,
>>
>> On 07/09/17 06:54, Dongjiu Geng wrote:
>>> In VHE mode, host kernel runs in the EL2 and can enable
>>> 'User Access Override' when fs==KERNEL_DS so that it can
>>> access kernel memory. However, PSTATE.UAO is set to 0 on
>>> an exception taken from EL1 to EL2. Thus when VHE is used
>>> and exception taken from a guest UAO will be disabled and
>>> host will use the incorrect PSTATE.UAO. So check and reset
>>> the PSTATE.UAO when switching to host.
>>
>> This would only be a problem if KVM were calling into world-switch with
>> fs==KERNEL_DS. I can't see where this happens.
>  Not only KVM, may also kernel sets the fs == KERNEL_DS before calling into world-switch

How? Please describe the exact sequence of event that lead to this
situation with the current code base.

	M.
-- 
Jazz is not dead. It just smells funny...