Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752572AbdLFOlG (ORCPT ); Wed, 6 Dec 2017 09:41:06 -0500 Received: from mx1.redhat.com ([209.132.183.28]:51562 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752211AbdLFOkZ (ORCPT ); Wed, 6 Dec 2017 09:40:25 -0500 Subject: Re: [PATCH v2] KVM: X86: Fix load RFLAGS w/o the fixed bit To: Wanpeng Li , linux-kernel@vger.kernel.org, kvm@vger.kernel.org Cc: Paolo Bonzini , =?UTF-8?B?UmFkaW0gS3LEjW3DocWZ?= , Wanpeng Li , Jim Mattson References: <1512561558-15470-1-git-send-email-wanpeng.li@hotmail.com> From: David Hildenbrand Organization: Red Hat GmbH Message-ID: Date: Wed, 6 Dec 2017 15:40:22 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.4.0 MIME-Version: 1.0 In-Reply-To: <1512561558-15470-1-git-send-email-wanpeng.li@hotmail.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.29]); Wed, 06 Dec 2017 14:40:24 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2188 Lines: 74 On 06.12.2017 12:59, Wanpeng Li wrote: > From: Wanpeng Li > > *** Guest State *** > CR0: actual=0x0000000000000030, shadow=0x0000000060000010, gh_mask=fffffffffffffff7 > CR4: actual=0x0000000000002050, shadow=0x0000000000000000, gh_mask=ffffffffffffe871 > CR3 = 0x00000000fffbc000 > RSP = 0x0000000000000000 RIP = 0x0000000000000000 > RFLAGS=0x00000000 DR7 = 0x0000000000000400 > ^^^^^^^^^^ > > The failed vmentry is triggered by the following testcase when ept=Y: > > #include > #include > #include > #include > #include > #include > #include > > long r[5]; > int main() > { > r[2] = open("/dev/kvm", O_RDONLY); > r[3] = ioctl(r[2], KVM_CREATE_VM, 0); > r[4] = ioctl(r[3], KVM_CREATE_VCPU, 7); > struct kvm_regs regs = { > .rflags = 0, > }; > ioctl(r[4], KVM_SET_REGS, ®s); > ioctl(r[4], KVM_RUN, 0); > } > > X86 RFLAGS bit 1 is fixed set, userspace can simply clearing bit 1 > of RFLAGS with KVM_SET_REGS ioctl which results in vmentry fails. > This patch fixes it by oring X86_EFLAGS_FIXED during ioctl. > > Suggested-by: Jim Mattson > Cc: Paolo Bonzini > Cc: Radim Krčmář > Cc: Jim Mattson > Signed-off-by: Wanpeng Li > --- > v1 -> v2: > * Oring X86_EFLAGS_FIXED > > virt/kvm/kvm_main.c | 1 + > 1 file changed, 1 insertion(+) > > diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c > index b55bad3..0f3f283 100644 > --- a/virt/kvm/kvm_main.c > +++ b/virt/kvm/kvm_main.c > @@ -2602,6 +2602,7 @@ static long kvm_vcpu_ioctl(struct file *filp, > r = PTR_ERR(kvm_regs); > goto out; > } > + kvm_regs->rflags |= X86_EFLAGS_FIXED; > r = kvm_arch_vcpu_ioctl_set_regs(vcpu, kvm_regs); > kfree(kvm_regs); > break; > Not sure if failing KVM_SET_REGS would be nicer, but maybe this has already been discussed. So this should be fine. Reviewed-by: David Hildenbrand -- Thanks, David / dhildenb