Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754213AbcDVJY1 (ORCPT ); Fri, 22 Apr 2016 05:24:27 -0400 Received: from szxga03-in.huawei.com ([119.145.14.66]:46055 "EHLO szxga03-in.huawei.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754103AbcDVJYY (ORCPT ); Fri, 22 Apr 2016 05:24:24 -0400 Date: Fri, 22 Apr 2016 17:21:03 +0800 From: Wei Yang To: Greg Kurz CC: Paolo Bonzini , , , , , , , David Hildenbrand , , Cornelia Huck , Paul Mackerras , David Gibson Subject: Re: [PATCH v4 2/2] KVM: move vcpu id checking to archs Message-ID: <20160422092103.GA3851@linux-gk3p> Reply-To: Wei Yang References: <146124809455.32509.15232948272580716135.stgit@bahia.huguette.org> <146124811255.32509.17679765789502091772.stgit@bahia.huguette.org> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Disposition: inline In-Reply-To: <146124811255.32509.17679765789502091772.stgit@bahia.huguette.org> User-Agent: Mutt/1.5.17 (2007-11-01) X-Originating-IP: [10.160.19.74] X-CFilter-Loop: Reflected X-Mirapoint-Virus-RAPID-Raw: score=unknown(0), refid=str=0001.0A090201.5719ED86.003E,ss=1,re=0.000,recu=0.000,reip=0.000,cl=1,cld=1,fgs=0, ip=0.0.0.0, so=2013-05-26 15:14:31, dmn=2013-03-21 17:37:32 X-Mirapoint-Loop-Id: 8b9a5d4a8c4bf11ccb1a038a1e1c8f87 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 4460 Lines: 120 Hi, Greg One confusion. There are 5 kvm_arch_vcpu_create() while in this patch you changed 2 of them. Some particular reason? On Thu, Apr 21, 2016 at 04:20:53PM +0200, Greg Kurz wrote: >Commit 338c7dbadd26 ("KVM: Improve create VCPU parameter (CVE-2013-4587)") >introduced a check to prevent potential kernel memory corruption in case >the vcpu id is too great. > >Unfortunately this check assumes vcpu ids grow in sequence with a common >difference of 1, which is wrong: archs are free to use vcpu id as they fit. >For example, QEMU originated vcpu ids for PowerPC cpus running in boot3s_hv >mode, can grow with a common difference of 2, 4 or 8: if KVM_MAX_VCPUS is >1024, guests may be limited down to 128 vcpus on POWER8. > >This means the check does not belong here and should be moved to some arch >specific function: kvm_arch_vcpu_create() looks like a good candidate. > >ARM and s390 already have such a check. > >I could not spot any path in the PowerPC or common KVM code where a vcpu >id is used as described in the above commit: I believe PowerPC can live >without this check. > >In the end, this patch simply moves the check to MIPS and x86. While here, >we also update the documentation to dissociate vcpu ids from the maximum >number of vcpus per virtual machine. > >Acked-by: James Hogan >Acked-by: Cornelia Huck >Signed-off-by: Greg Kurz >--- >v4: - updated subject for more clarity on what the patch does > - added James's and Connie's A-b tags > - updated documentation > > Documentation/virtual/kvm/api.txt | 7 +++---- > arch/mips/kvm/mips.c | 7 ++++++- > arch/x86/kvm/x86.c | 3 +++ > virt/kvm/kvm_main.c | 3 --- > 4 files changed, 12 insertions(+), 8 deletions(-) > >diff --git a/Documentation/virtual/kvm/api.txt b/Documentation/virtual/kvm/api.txt >index 4d0542c5206b..486a1d783b82 100644 >--- a/Documentation/virtual/kvm/api.txt >+++ b/Documentation/virtual/kvm/api.txt >@@ -199,11 +199,10 @@ Type: vm ioctl > Parameters: vcpu id (apic id on x86) > Returns: vcpu fd on success, -1 on error > >-This API adds a vcpu to a virtual machine. The vcpu id is a small integer >-in the range [0, max_vcpus). >+This API adds a vcpu to a virtual machine. The vcpu id is a positive integer. > >-The recommended max_vcpus value can be retrieved using the KVM_CAP_NR_VCPUS of >-the KVM_CHECK_EXTENSION ioctl() at run-time. >+The recommended maximum number of vcpus (max_vcpus) can be retrieved using the >+KVM_CAP_NR_VCPUS of the KVM_CHECK_EXTENSION ioctl() at run-time. > The maximum possible value for max_vcpus can be retrieved using the > KVM_CAP_MAX_VCPUS of the KVM_CHECK_EXTENSION ioctl() at run-time. > >diff --git a/arch/mips/kvm/mips.c b/arch/mips/kvm/mips.c >index 70ef1a43c114..0278ea146db5 100644 >--- a/arch/mips/kvm/mips.c >+++ b/arch/mips/kvm/mips.c >@@ -248,9 +248,14 @@ struct kvm_vcpu *kvm_arch_vcpu_create(struct kvm *kvm, unsigned int id) > int err, size, offset; > void *gebase; > int i; >+ struct kvm_vcpu *vcpu; > >- struct kvm_vcpu *vcpu = kzalloc(sizeof(struct kvm_vcpu), GFP_KERNEL); >+ if (id >= KVM_MAX_VCPUS) { >+ err = -EINVAL; >+ goto out; >+ } > >+ vcpu = kzalloc(sizeof(struct kvm_vcpu), GFP_KERNEL); > if (!vcpu) { > err = -ENOMEM; > goto out; >diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c >index 9b7798c7b210..7738202edcce 100644 >--- a/arch/x86/kvm/x86.c >+++ b/arch/x86/kvm/x86.c >@@ -7358,6 +7358,9 @@ struct kvm_vcpu *kvm_arch_vcpu_create(struct kvm *kvm, > { > struct kvm_vcpu *vcpu; > >+ if (id >= KVM_MAX_VCPUS) >+ return ERR_PTR(-EINVAL); >+ > if (check_tsc_unstable() && atomic_read(&kvm->online_vcpus) != 0) > printk_once(KERN_WARNING > "kvm: SMP vm created on host with unstable TSC; " >diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c >index 4fd482fb9260..6b6cca3cb488 100644 >--- a/virt/kvm/kvm_main.c >+++ b/virt/kvm/kvm_main.c >@@ -2272,9 +2272,6 @@ static int kvm_vm_ioctl_create_vcpu(struct kvm *kvm, u32 id) > int r; > struct kvm_vcpu *vcpu; > >- if (id >= KVM_MAX_VCPUS) >- return -EINVAL; >- > vcpu = kvm_arch_vcpu_create(kvm, id); > if (IS_ERR(vcpu)) > return PTR_ERR(vcpu); > >-- >To unsubscribe from this list: send the line "unsubscribe kvm" in >the body of a message to majordomo@vger.kernel.org >More majordomo info at http://vger.kernel.org/majordomo-info.html -- Richard Yang\nHelp you, Help me