linux-kernel - Re: [PATCH 1/4] KVM: MMU: fix forgot reserved bits check in speculative path

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Date:	Wed, 14 Jul 2010 17:27:21 +0300
From:	Avi Kivity <avi@...hat.com>
To:	Xiao Guangrong <xiaoguangrong@...fujitsu.com>
CC:	LKML <linux-kernel@...r.kernel.org>,
	KVM list <kvm@...r.kernel.org>,
	Marcelo Tosatti <mtosatti@...hat.com>
Subject: Re: [PATCH 1/4] KVM: MMU: fix forgot reserved bits check in speculative
 path

On 07/14/2010 04:24 PM, Xiao Guangrong wrote:
>
> Avi Kivity wrote:
>
>    
>>> +
>>> +            if (!!is_pae(vcpu) != sp->role.cr4_pae ||
>>> +                  is_nx(vcpu) != sp->role.nxe)
>>> +                continue;
>>> +
>>>
>>>        
>> Do we also need to check cr0.wp?  I think so.
>>      
> I think it's not too bad since we just decrease the access right, for example,
> we mark the mapping readonly for cr0.wp=0's page, the later write-access will
> cause #PF, and the read-access is OK.
>    

If current cr0.wp=0 and sp->role.cr0_wp=1, that's fine, but the other 
way round can relax permissions too much, marking a kernel page writeable.

-- 
I have a truly marvellous patch that fixes the bug which this
signature is too narrow to contain.

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