Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933130AbdGSWtB (ORCPT ); Wed, 19 Jul 2017 18:49:01 -0400 Received: from mail-oi0-f65.google.com ([209.85.218.65]:38402 "EHLO mail-oi0-f65.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932437AbdGSWs7 (ORCPT ); Wed, 19 Jul 2017 18:48:59 -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> From: Wanpeng Li Date: Thu, 20 Jul 2017 06:48:58 +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 v6JMn7aQ003307 Content-Length: 3572 Lines: 91 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? Regards, Wanpeng Li