From mboxrd@z Thu Jan 1 00:00:00 1970 From: Marcelo Tosatti Subject: Re: KVM: VMX: fix use after free of vmx->loaded_vmcs Date: Fri, 3 Jan 2014 17:36:28 -0200 Message-ID: <20140103193628.GA17605@amt.cnet> References: <20140103190051.GA16151@amt.cnet> <52C70F0B.7020406@web.de> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: kvm-devel , Paolo Bonzini To: Jan Kiszka Return-path: Received: from mx1.redhat.com ([209.132.183.28]:43882 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751139AbaACTgn (ORCPT ); Fri, 3 Jan 2014 14:36:43 -0500 Content-Disposition: inline In-Reply-To: <52C70F0B.7020406@web.de> Sender: kvm-owner@vger.kernel.org List-ID: On Fri, Jan 03, 2014 at 08:27:07PM +0100, Jan Kiszka wrote: > On 2014-01-03 20:00, Marcelo Tosatti wrote: > > > > After free_loaded_vmcs executes, the "loaded_vmcs" structure > > is kfreed, and now vmx->loaded_vmcs points to a kfreed area. > > Subsequent free_loaded_vmcs then attempts to manipulate > > vmx->loaded_vmcs. > > Cannot follow yet. How precisely do we call free_loaded_vmcs twice on > the same loaded_vmcs? You don't: nested_free_all_saved_vmcss calls kfree(item). item is struct vmcs02_list *, which is: /* Used to remember the last vmcs02 used for some recently used vmcs12s * */ struct vmcs02_list { struct list_head list; gpa_t vmptr; struct loaded_vmcs vmcs02; }; And vmx->loaded_vmcs = &item->vmcs02. > I thought the frees triggered by free_nested -> > nested_free_all_saved_vmcss stay away from vmx->loaded_vmcs, no? Stays away as far as free_loaded_vmcs, yes. Except it frees the structure pointed to by vmx->loaded_vmcs. The separate question is about when is vmcs01 ever allocated again if freed by nested_free_all_saved_vmcss (the other email). > Jan > > > > > Switch the order to avoid the problem. > > > > https://bugzilla.redhat.com/show_bug.cgi?id=1047892 > > > > Signed-off-by: Marcelo Tosatti > > > > diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c > > index da7837e..2efa33f0 100644 > > --- a/arch/x86/kvm/vmx.c > > +++ b/arch/x86/kvm/vmx.c > > @@ -7332,8 +7332,8 @@ static void vmx_free_vcpu(struct kvm_vcpu *vcpu) > > struct vcpu_vmx *vmx = to_vmx(vcpu); > > > > free_vpid(vmx); > > - free_nested(vmx); > > free_loaded_vmcs(vmx->loaded_vmcs); > > + free_nested(vmx); > > kfree(vmx->guest_msrs); > > kvm_vcpu_uninit(vcpu); > > kmem_cache_free(kvm_vcpu_cache, vmx); > > > >