From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752096AbdFHNjC (ORCPT ); Thu, 8 Jun 2017 09:39:02 -0400 Received: from mx1.redhat.com ([209.132.183.28]:58356 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751946AbdFHNi7 (ORCPT ); Thu, 8 Jun 2017 09:38:59 -0400 DMARC-Filter: OpenDMARC Filter v1.3.2 mx1.redhat.com CEA13C05FFC6 Authentication-Results: ext-mx08.extmail.prod.ext.phx2.redhat.com; dmarc=none (p=none dis=none) header.from=redhat.com Authentication-Results: ext-mx08.extmail.prod.ext.phx2.redhat.com; spf=pass smtp.mailfrom=pbonzini@redhat.com DKIM-Filter: OpenDKIM Filter v2.11.0 mx1.redhat.com CEA13C05FFC6 Subject: Re: [PATCH v2 1/2] KVM: cpuid: Fix read/write out-of-bounds vulnerability in cpuid emulation To: Wanpeng Li , linux-kernel@vger.kernel.org, kvm@vger.kernel.org Cc: =?UTF-8?B?UmFkaW0gS3LEjW3DocWZ?= , Wanpeng Li , Moguofang , stable@vger.kernel.org References: <1496910128-87057-1-git-send-email-wanpeng.li@hotmail.com> From: Paolo Bonzini Message-ID: <562ffd39-83ba-1d64-6d7d-22f66a0716fe@redhat.com> Date: Thu, 8 Jun 2017 15:38:54 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.1.0 MIME-Version: 1.0 In-Reply-To: <1496910128-87057-1-git-send-email-wanpeng.li@hotmail.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.32]); Thu, 08 Jun 2017 13:38:59 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 08/06/2017 10:22, Wanpeng Li wrote: > From: Wanpeng Li > > If "i" is the last element in the vcpu->arch.cpuid_entries[] array, it > potentially can be exploited the vulnerability. this will out-of-bounds > read and write the unused memory in host OS. > > As Paolo pointed: > >>> /* when no next entry is found, the current entry[i] is reselected */ >>> - for (j = i + 1; ; j = (j + 1) % nent) { >>> - struct kvm_cpuid_entry2 *ej = &vcpu->arch.cpuid_entries[j]; >>> - if (ej->function == e->function) { >> >> It reads ej->maxphyaddr, which is user controlled. >> >>> - ej->flags |= KVM_CPUID_FLAG_STATE_READ_NEXT; >> >> After cpuid_entries there is >> >> int maxphyaddr; >> struct x86_emulate_ctxt emulate_ctxt; /* 16-byte aligned */ >> >> So indeed we have: >> >> - cpuid_entries at offset 1B50 (6992) >> - maxphyaddr at offset 27D0 (6992 + 3200 = 10192) >> - padding at 27D4...27DF >> - emulate_ctxt at 27E0 >> >> So this indeed writes in the padding. Pfew, writing the ops field of >> emulate_ctxt would have been much worse. > > This patch fixes it by modding the index to avoid the out-of-bounds. At > the worst case, i == j and ej->function == e->function, the loop can bail > out. > > Reported-by: Moguofang > Cc: Paolo Bonzini > Cc: Radim Krčmář > Cc: Moguofang > Cc: stable@vger.kernel.org > Signed-off-by: Wanpeng Li > --- > v1 -> v2: > * update patch description Queued, thanks. Paolo > > arch/x86/kvm/cpuid.c | 19 ++++++++++--------- > 1 file changed, 10 insertions(+), 9 deletions(-) > > diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c > index a181ae7..b927a42 100644 > --- a/arch/x86/kvm/cpuid.c > +++ b/arch/x86/kvm/cpuid.c > @@ -779,19 +779,20 @@ int kvm_dev_ioctl_get_cpuid(struct kvm_cpuid2 *cpuid, > > static int move_to_next_stateful_cpuid_entry(struct kvm_vcpu *vcpu, int i) > { > + int j = i, nent = vcpu->arch.cpuid_nent; > struct kvm_cpuid_entry2 *e = &vcpu->arch.cpuid_entries[i]; > - int j, nent = vcpu->arch.cpuid_nent; > + struct kvm_cpuid_entry2 *ej; > > e->flags &= ~KVM_CPUID_FLAG_STATE_READ_NEXT; > /* when no next entry is found, the current entry[i] is reselected */ > - for (j = i + 1; ; j = (j + 1) % nent) { > - struct kvm_cpuid_entry2 *ej = &vcpu->arch.cpuid_entries[j]; > - if (ej->function == e->function) { > - ej->flags |= KVM_CPUID_FLAG_STATE_READ_NEXT; > - return j; > - } > - } > - return 0; /* silence gcc, even though control never reaches here */ > + do { > + j = (j + 1) % nent; > + ej = &vcpu->arch.cpuid_entries[j]; > + } while(ej->function != e->function); > + > + ej->flags |= KVM_CPUID_FLAG_STATE_READ_NEXT; > + > + return j; > } > > /* find an entry with matching function, matching index (if needed), and that >