From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751859AbdKVIpm (ORCPT ); Wed, 22 Nov 2017 03:45:42 -0500 Received: from userp1040.oracle.com ([156.151.31.81]:24160 "EHLO userp1040.oracle.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751588AbdKVIpk (ORCPT ); Wed, 22 Nov 2017 03:45:40 -0500 Message-ID: <5A153926.7030004@ORACLE.COM> Date: Wed, 22 Nov 2017 10:45:26 +0200 From: Liran Alon User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:24.0) Gecko/20100101 Thunderbird/24.5.0 MIME-Version: 1.0 To: Wanpeng Li , linux-kernel@vger.kernel.org, kvm@vger.kernel.org CC: Paolo Bonzini , =?UTF-8?B?UmFkaW0gS3LEjW3DocWZ?= , Wanpeng Li , Dmitry Vyukov Subject: Re: [PATCH] KVM: VMX: Fix vmx->nested freeing when no SMI handler References: <1511337410-8100-1-git-send-email-wanpeng.li@hotmail.com> In-Reply-To: <1511337410-8100-1-git-send-email-wanpeng.li@hotmail.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Source-IP: aserv0021.oracle.com [141.146.126.233] Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 22/11/17 09:56, Wanpeng Li wrote: > From: Wanpeng Li > > Reported by syzkaller: > > ------------[ cut here ]------------ > WARNING: CPU: 5 PID: 2939 at arch/x86/kvm/vmx.c:3844 free_loaded_vmcs+0x77/0x80 [kvm_intel] > CPU: 5 PID: 2939 Comm: repro Not tainted 4.14.0+ #26 > RIP: 0010:free_loaded_vmcs+0x77/0x80 [kvm_intel] > Call Trace: > vmx_free_vcpu+0xda/0x130 [kvm_intel] > kvm_arch_destroy_vm+0x192/0x290 [kvm] > kvm_put_kvm+0x262/0x560 [kvm] > kvm_vm_release+0x2c/0x30 [kvm] > __fput+0x190/0x370 > task_work_run+0xa1/0xd0 > do_exit+0x4d2/0x13e0 > do_group_exit+0x89/0x140 > get_signal+0x318/0xb80 > do_signal+0x8c/0xb40 > exit_to_usermode_loop+0xe4/0x140 > syscall_return_slowpath+0x206/0x230 > entry_SYSCALL_64_fastpath+0x98/0x9a > > The syzkaller testcase will execute VMXON/VMLAUCH instructions, so the > vmx->nested stuff is populated, it will also issue KVM_SMI ioctl. However, > the testcase is just a simple c program and not be lauched by something > like seabios which implements smi_handler. Commit 05cade71cf (KVM: nSVM: > fix SMI injection in guest mode) gets out of guest mode and set nested.vmxon > to false for the duration of SMM according to SDM 34.14.1 "leave VMX > operation" upon entering SMM. We can't alloc/free the vmx->nested stuff > each time when entering/exiting SMM since it will induce more overhead. So > the function vmx_pre_enter_smm() marks nested.vmxon false even if vmx->nested > stuff is still populated. What it expected is em_rsm() can mark nested.vmxon > to be true again. However, the smi_handler/rsm will not execute since there > is no something like seabios in this scenario. The function free_nested() > fails to free the vmx->nested stuff since the vmx->nested.vmxon is false > which results in the above warning. > > This patch fixes it by also considering the no SMI handler case, luckily > vmx->nested.smm.vmxon is marked according to the value of vmx->nested.vmxon > in vmx_pre_enter_smm(), we can take advantage of it and free vmx->nested > stuff when L1 goes down. > > Reported-by: Dmitry Vyukov > Cc: Paolo Bonzini > Cc: Radim Krčmář > Cc: Dmitry Vyukov > Fixes: 05cade71cf (KVM: nSVM: fix SMI injection in guest mode) > Signed-off-by: Wanpeng Li > --- > arch/x86/kvm/vmx.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c > index dccc0f7..ed22425 100644 > --- a/arch/x86/kvm/vmx.c > +++ b/arch/x86/kvm/vmx.c > @@ -7372,7 +7372,7 @@ static inline void nested_release_vmcs12(struct vcpu_vmx *vmx) > */ > static void free_nested(struct vcpu_vmx *vmx) > { > - if (!vmx->nested.vmxon) > + if (!vmx->nested.vmxon && !vmx->nested.smm.vmxon) > return; > > vmx->nested.vmxon = false; > Funny bug. Great analysis. Reviewed-by: Liran Alon