Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753522AbdIRJ7M (ORCPT ); Mon, 18 Sep 2017 05:59:12 -0400 Received: from mga14.intel.com ([192.55.52.115]:55043 "EHLO mga14.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753332AbdIRJ7J (ORCPT ); Mon, 18 Sep 2017 05:59:09 -0400 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.42,412,1500966000"; d="scan'208";a="1196197601" Subject: Re: [PATCH v3 2/5] KVM: MMU: check guest CR3 reserved bits based on its physical address width. To: Paolo Bonzini , Jim Mattson Cc: kvm list , LKML , =?UTF-8?B?UmFkaW0gS3LEjW3DocWZ?= , Thomas Gleixner , Ingo Molnar , "H . Peter Anvin" , xiaoguangrong@tencent.com, Joerg Roedel References: <1503577676-12345-1-git-send-email-yu.c.zhang@linux.intel.com> <1503577676-12345-3-git-send-email-yu.c.zhang@linux.intel.com> <6b811eb0-1204-08b1-61c2-0030fa450ad4@redhat.com> From: Yu Zhang Message-ID: Date: Mon, 18 Sep 2017 17:35:19 +0800 User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:52.0) Gecko/20100101 Thunderbird/52.3.0 MIME-Version: 1.0 In-Reply-To: <6b811eb0-1204-08b1-61c2-0030fa450ad4@redhat.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit Content-Language: en-US Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1455 Lines: 45 On 9/18/2017 4:41 PM, Paolo Bonzini wrote: > On 18/09/2017 10:15, Yu Zhang wrote: >>> static bool emulator_get_cpuid(struct x86_emulate_ctxt *ctxt, >>> u32 *eax, u32 *ebx, u32 *ecx, u32 *edx, bool >>> check_limit) >>> { >>> return kvm_cpuid(emul_to_vcpu(ctxt), eax, ebx, ecx, edx, >>> check_limit); >>> } >>> >>> And: >>> >>> bool kvm_cpuid(struct kvm_vcpu *vcpu, u32 *eax, u32 *ebx, >>> u32 *ecx, u32 *edx, bool check_limit) >>> { >>> u32 function = *eax, index = *ecx; >>> struct kvm_cpuid_entry2 *best; >>> bool entry_found = true; >>> ... >>> >>> Doesn't this immediately try to dereference a NULL pointer? How much >>> testing have you done of this code? >> Thanks Jim. >> I have tested this code in a simulator to successfully boot a VM in >> shadow mode. Seems this code is not covered(but I am now still >> perplexed why this is not covered). Any possibility that the >> check_cr_write() is not triggered when emulating the cr operations? > CR moves usually don't go through the emulator (the main exception is > emulation of invalid guest state when the processor doesn't support > unrestricted_guest=1, but even that is unlikely to happen with > EFER.LMA=1). This explains why you didn't see the failure. Oh, right. It normally goes to handle_cr(). Thanks, Paolo. Yu > >> Anyway, this should be a bug and thanks for pointing this out, and >> I'll send out the fix later. > Thanks, > > Paolo >