Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755743AbdGSXBS (ORCPT ); Wed, 19 Jul 2017 19:01:18 -0400 Received: from mail-oi0-f67.google.com ([209.85.218.67]:33359 "EHLO mail-oi0-f67.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755410AbdGSXBP (ORCPT ); Wed, 19 Jul 2017 19:01:15 -0400 MIME-Version: 1.0 In-Reply-To: <539DB8ED-1315-41DA-8F61-1036D44E5E48@gmail.com> References: <1499757180-20439-1-git-send-email-wanpeng.li@hotmail.com> <20170719112926.GA13502@potion> <20170719161952.GC17303@potion> <539DB8ED-1315-41DA-8F61-1036D44E5E48@gmail.com> From: Wanpeng Li Date: Thu, 20 Jul 2017 07:01:14 +0800 Message-ID: Subject: Re: [PATCH v2] KVM: VMX: Fix invalid guest state detection after task-switch emulation To: Nadav Amit Cc: =?UTF-8?B?UmFkaW0gS3LEjW3DocWZ?= , "linux-kernel@vger.kernel.org" , kvm , Paolo Bonzini , Wanpeng Li Content-Type: text/plain; charset="UTF-8" Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Transfer-Encoding: 8bit X-MIME-Autoconverted: from quoted-printable to 8bit by nfs id v6JN1MSf003362 Content-Length: 4158 Lines: 102 2017-07-20 6:53 GMT+08:00 Nadav Amit : > Wanpeng Li wrote: > >> 2017-07-20 0:25 GMT+08:00 Nadav Amit : >>> Radim Krčmář wrote: >>> >>>> 2017-07-19 08:14-0700, Nadav Amit: >>>>> Radim Krčmář wrote: >>>>>> @@ -2363,6 +2368,8 @@ static unsigned long vmx_get_rflags(struct kvm_vcpu *vcpu) >>>>>> >>>>>> static void vmx_set_rflags(struct kvm_vcpu *vcpu, unsigned long rflags) >>>>>> { >>>>>> + unsigned long old_rflags = to_vmx(vcpu)->rflags; >>>>> >>>>> It assumes rflags was decached from the VMCS before. Probably it is true, but… >>>> >>>> Right, it's better to use accessors everywhere, thanks. >>>> The line should read: >>>> >>>> + unsigned long old_rflags = vmx_get_rflags(vcpu); >>>> >>>> ---8<--- >>>> This can be reproduced by EPT=1, unrestricted_guest=N, emulate_invalid_state=Y >>>> or EPT=0, the trace of kvm-unit-tests/taskswitch2.flat is like below, it >>>> tries to emulate invalid guest state task-switch: >>>> >>>> kvm_exit: reason TASK_SWITCH rip 0x0 info 40000058 0 >>>> kvm_emulate_insn: 42000:0:0f 0b (0x2) >>>> kvm_emulate_insn: 42000:0:0f 0b (0x2) failed >>>> kvm_inj_exception: #UD (0x0) >>>> kvm_entry: vcpu 0 >>>> kvm_exit: reason TASK_SWITCH rip 0x0 info 40000058 0 >>>> kvm_emulate_insn: 42000:0:0f 0b (0x2) >>>> kvm_emulate_insn: 42000:0:0f 0b (0x2) failed >>>> kvm_inj_exception: #UD (0x0) >>>> >>>> It appears that the task-switch emulation updates rflags (and vm86 flag) >>>> only after the segments are loaded, causing vmx->emulation_required to >>>> be set, when in fact invalid guest state emulation is not needed. >>>> >>>> This patch fixes it by updating vmx->emulation_required after the rflags >>>> (and vm86 flag) is updated. >>>> >>>> Suggested-by: Nadav Amit >>>> Signed-off-by: Wanpeng Li >>>> [Wanpeng wrote the commit message with initial patch and Radim moved the >>>> update to vmx_set_rflags and added Paolo's suggestion for the check.] >>>> Signed-off-by: Radim Krčmář >>>> --- >>>> arch/x86/kvm/vmx.c | 15 ++++++++++----- >>>> 1 file changed, 10 insertions(+), 5 deletions(-) >>>> >>>> diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c >>>> index 84e62acf2dd8..a776aea0043a 100644 >>>> --- a/arch/x86/kvm/vmx.c >>>> +++ b/arch/x86/kvm/vmx.c >>>> @@ -2326,6 +2326,11 @@ static void vmx_vcpu_put(struct kvm_vcpu *vcpu) >>>> __vmx_load_host_state(to_vmx(vcpu)); >>>> } >>>> >>>> +static bool emulation_required(struct kvm_vcpu *vcpu) >>>> +{ >>>> + return emulate_invalid_guest_state && !guest_state_valid(vcpu); >>>> +} >>>> + >>>> static void vmx_decache_cr0_guest_bits(struct kvm_vcpu *vcpu); >>>> >>>> /* >>>> @@ -2363,6 +2368,8 @@ static unsigned long vmx_get_rflags(struct kvm_vcpu *vcpu) >>>> >>>> static void vmx_set_rflags(struct kvm_vcpu *vcpu, unsigned long rflags) >>>> { >>>> + unsigned long old_rflags = vmx_get_rflags(vcpu); >>>> + >>>> __set_bit(VCPU_EXREG_RFLAGS, (ulong *)&vcpu->arch.regs_avail); >>>> to_vmx(vcpu)->rflags = rflags; >>>> if (to_vmx(vcpu)->rmode.vm86_active) { >>>> @@ -2370,6 +2377,9 @@ static void vmx_set_rflags(struct kvm_vcpu *vcpu, unsigned long rflags) >>>> rflags |= X86_EFLAGS_IOPL | X86_EFLAGS_VM; >>>> } >>>> vmcs_writel(GUEST_RFLAGS, rflags); >>>> + >>>> + if ((old_rflags ^ rflags) & X86_EFLAGS_VM) >>>> + to_vmx(vcpu)->emulation_required = emulation_required(vcpu); >>> >>> Sorry for not pointing it before, but here you compare the old_rflags with >>> the new rflags but after you already “massaged” it. So the value you compare >>> with is not what the guest “sees”. >> >> So you mean we should use unsigned long old_rflags = >> vmcs_readl(GUEST_RFLAGS); right? > > No. The problem is not with old_rflags now, but with rflags. If vm86_active, > then rflags is changed and you don’t compare the guest-visible rflags > anymore. Ah, I see. So we should compare the old_flags with the rmode->save_rflags(guest-visible rflags) instead of the rflags (shadow rflags), right? Regards, Wanpeng Li