From mboxrd@z Thu Jan 1 00:00:00 1970 From: Avi Kivity Subject: Re: [PATCH 2/2] KVM: MMU: fix relaxing permission Date: Thu, 27 May 2010 13:10:27 +0300 Message-ID: <4BFE4513.8090606@redhat.com> References: <4BFC8B0D.2060106@cn.fujitsu.com> <4BFC8B8C.7010402@cn.fujitsu.com> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Cc: Marcelo Tosatti , LKML , KVM list To: Xiao Guangrong Return-path: In-Reply-To: <4BFC8B8C.7010402@cn.fujitsu.com> Sender: linux-kernel-owner@vger.kernel.org List-Id: kvm.vger.kernel.org On 05/26/2010 05:46 AM, Xiao Guangrong wrote: > There is a relaxing permission operation in set_spte(): > > if guest's CR0.WP is not set and R/W #PF occurs in supervisor-level, > the mapping path might set to writable, then user can allow to write. > > @@ -1859,8 +1859,7 @@ static int set_spte(struct kvm_vcpu *vcpu, u64 *sptep, > > spte |= (u64)pfn<< PAGE_SHIFT; > > - if ((pte_access& ACC_WRITE_MASK) > - || (write_fault&& !is_write_protection(vcpu)&& !user_fault)) { > + if (pte_access& ACC_WRITE_MASK) { > > The host always sets cr0.wp (in shadow mode) so we can write protect page tables. So when the guest clears cr0.wp, we emulate a gpte with gpte.w=0 and gpte.u=1 in two ways: - spte.w=1, spte.u=0: this will allow the guest kernel to write but trap on guest user access - spte.w=0, spte.u=1: allows guest user access but traps on guest kernel writes If the guest attempts an access that is currently disallowed, we switch to the other spte encoding. -- error compiling committee.c: too many arguments to function