Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933640AbdGSXKF (ORCPT ); Wed, 19 Jul 2017 19:10:05 -0400 Received: from mail-oi0-f66.google.com ([209.85.218.66]:34141 "EHLO mail-oi0-f66.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S933620AbdGSXJ7 (ORCPT ); Wed, 19 Jul 2017 19:09:59 -0400 MIME-Version: 1.0 In-Reply-To: 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 07:09:58 +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 v6JNA99J003384 Content-Length: 4791 Lines: 112 2017-07-20 7:06 GMT+08:00 Nadav Amit : > Wanpeng Li wrote: > >> 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? > > Not exactly, since rmode->save_rflags are invalid if !vm86_active. Instead, > I think you should have a save_rflags variable on the stack that would hold > the rflags before “massaging” and use it instead. Thanks for pointing out :) I will send out a new version, in addition, thanks Radim's help for these two versions. :) Regards, Wanpeng Li