linux-kernel - Re: [PATCH 1/4] KVM: MMU: fix permission

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Date:	Wed, 30 Mar 2016 09:56:36 +0800
From:	Xiao Guangrong <guangrong.xiao@...ux.intel.com>
To:	Paolo Bonzini <pbonzini@...hat.com>
Cc:	gleb@...nel.org, mtosatti@...hat.com, kvm@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/4] KVM: MMU: fix permission_fault()



On 03/30/2016 04:09 AM, Paolo Bonzini wrote:
>
>
> On 29/03/2016 19:43, Xiao Guangrong wrote:
>> Based on the SDM:
>> PK flag (bit 5).
>> This flag is 1 if (1) IA32_EFER.LMA = CR4.PKE = 1; (2) the access
>> causing the page-fault exception was a data access; (3) the linear
>> address was a user-mode address with protection key i; and (5) the PKRU
>> register (see Section 4.6.2) is such that either (a) ADi = 1; or (b) the
>> following all hold: (i) WDi = 1; (ii) the access is a write access; and
>> (iii) either CR0.WP = 1 or the access causing the page-fault exception
>> was a user-mode access.
>>
>> So I think PKEY check and ordinary check are independent, i.e, PFEC.PKEY
>> may be set even if the on permission on the page table is not adequate.
>
> x86/access.flat is currently using the "other" definition, i.e., PFEC.PK
> is only set if W=1 or CR0.WP=0 && PFEC.U=0 or PFEC.W=0.  Can you use it
> (with ept=1 of course) to check what the processor is doing?
>

Sure.

And ept=1 is hard to trigger MMU issue, i am enabling PKEY on shadow
MMU, let's see what will happen. ;)