linux-kernel - Re: [PATCH v5 1/9] KVM: MMU: fix forgot reserved bits check in speculative path

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Date:	Sun, 11 Jul 2010 15:24:58 +0300
From:	Avi Kivity <avi@...hat.com>
To:	Xiao Guangrong <xiaoguangrong@...fujitsu.com>
CC:	Marcelo Tosatti <mtosatti@...hat.com>,
	LKML <linux-kernel@...r.kernel.org>,
	KVM list <kvm@...r.kernel.org>
Subject: Re: [PATCH v5 1/9] KVM: MMU: fix forgot reserved bits check in speculative
 path

On 07/06/2010 01:44 PM, Xiao Guangrong wrote:
> In the speculative path, we should check guest pte's reserved bits just as
> the real processor does
>
> Reported-by: Marcelo Tosatti<mtosatti@...hat.com>
> Signed-off-by: Xiao Guangrong<xiaoguangrong@...fujitsu.com>
> ---
>   arch/x86/kvm/mmu.c         |    3 +++
>   arch/x86/kvm/paging_tmpl.h |    3 ++-
>   2 files changed, 5 insertions(+), 1 deletions(-)
>
> diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
> index 104756b..3dcd55d 100644
> --- a/arch/x86/kvm/mmu.c
> +++ b/arch/x86/kvm/mmu.c
> @@ -2781,6 +2781,9 @@ void kvm_mmu_pte_write(struct kvm_vcpu *vcpu, gpa_t gpa,
>   		break;
>   	}
>
> +	if (is_rsvd_bits_set(vcpu, gentry, PT_PAGE_TABLE_LEVEL))
> +		gentry = 0;
> +
>    

That only works if the gpte is for the same mode as the current vcpu mmu 
mode.  In some cases it is too strict (vcpu in pae mode writing a 32-bit 
gpte), which is not too bad, in some cases it is too permissive (vcpu in 
nonpae mode writing a pae gpte).

(once upon a time mixed modes were rare, only on OS setup, but with 
nested virt they happen all the time).

>   	mmu_guess_page_from_pte_write(vcpu, gpa, gentry);
>   	spin_lock(&vcpu->kvm->mmu_lock);
>   	if (atomic_read(&vcpu->kvm->arch.invlpg_counter) != invlpg_counter)
> diff --git a/arch/x86/kvm/paging_tmpl.h b/arch/x86/kvm/paging_tmpl.h
> index dfb2720..19f0077 100644
> --- a/arch/x86/kvm/paging_tmpl.h
> +++ b/arch/x86/kvm/paging_tmpl.h
> @@ -628,7 +628,8 @@ static int FNAME(sync_page)(struct kvm_vcpu *vcpu, struct kvm_mmu_page *sp,
>   		pte_gpa = first_pte_gpa + i * sizeof(pt_element_t);
>
>   		if (kvm_read_guest_atomic(vcpu->kvm, pte_gpa,&gpte,
> -					  sizeof(pt_element_t)))
> +					  sizeof(pt_element_t)) ||
> +		      is_rsvd_bits_set(vcpu, gpte, PT_PAGE_TABLE_LEVEL))
>   			return -EINVAL;
>    

This is better done a few lines down where we check for 
!is_present_gpte(), no?

-- 
error compiling committee.c: too many arguments to function

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