linux-kernel - Re: [PATCH 1/3] KVM: MMU: fix smap permission check

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Message-ID: <554B311D.2010701@redhat.com>
Date:	Thu, 07 May 2015 11:32:13 +0200
From:	Paolo Bonzini <pbonzini@...hat.com>
To:	Xiao Guangrong <guangrong.xiao@...ux.intel.com>
CC:	gleb@...nel.org, mtosatti@...hat.com, kvm@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/3] KVM: MMU: fix smap permission check



On 07/05/2015 10:20, Xiao Guangrong wrote:
> Current permission check assumes that RSVD bit in PFEC is always zero,
> however, it is not true since MMIO #PF will use it to quickly identify
> MMIO access
> 
> Fix it by clearing the bit if walking guest page table is needed
> 
> Signed-off-by: Xiao Guangrong <guangrong.xiao@...ux.intel.com>
> ---
>  arch/x86/kvm/mmu.h         | 2 ++
>  arch/x86/kvm/paging_tmpl.h | 7 +++++++
>  2 files changed, 9 insertions(+)
> 
> diff --git a/arch/x86/kvm/mmu.h b/arch/x86/kvm/mmu.h
> index c7d6563..06eb2fc 100644
> --- a/arch/x86/kvm/mmu.h
> +++ b/arch/x86/kvm/mmu.h
> @@ -166,6 +166,8 @@ static inline bool permission_fault(struct kvm_vcpu *vcpu, struct kvm_mmu *mmu,
>  	int index = (pfec >> 1) +
>  		    (smap >> (X86_EFLAGS_AC_BIT - PFERR_RSVD_BIT + 1));
>  
> +	WARN_ON(pfec & PFERR_RSVD_MASK);
> +
>  	return (mmu->permissions[index] >> pte_access) & 1;
>  }
>  
> diff --git a/arch/x86/kvm/paging_tmpl.h b/arch/x86/kvm/paging_tmpl.h
> index fd49c86..6e6d115 100644
> --- a/arch/x86/kvm/paging_tmpl.h
> +++ b/arch/x86/kvm/paging_tmpl.h
> @@ -718,6 +718,13 @@ static int FNAME(page_fault)(struct kvm_vcpu *vcpu, gva_t addr, u32 error_code,
>  					      mmu_is_nested(vcpu));
>  		if (likely(r != RET_MMIO_PF_INVALID))
>  			return r;
> +
> +		/*
> +		 * page fault with PFEC.RSVD  = 1 is caused by shadow
> +		 * page fault, should not be used to walk guest page
> +		 * table.
> +		 */
> +		error_code &= ~PFERR_RSVD_MASK;
>  	};
>  
>  	r = mmu_topup_memory_caches(vcpu);
> 

Applied.

For the other patches I'm waiting for an answer re. kvm_mmu_pte_write.

Thanks,

Paolo
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