From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-8.5 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED,USER_AGENT_SANE_1 autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id D5BADC4CEC6 for ; Fri, 13 Sep 2019 01:54:06 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id B034B20692 for ; Fri, 13 Sep 2019 01:54:06 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726905AbfIMByF (ORCPT ); Thu, 12 Sep 2019 21:54:05 -0400 Received: from mga12.intel.com ([192.55.52.136]:31929 "EHLO mga12.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726262AbfIMByF (ORCPT ); Thu, 12 Sep 2019 21:54:05 -0400 X-Amp-Result: UNKNOWN X-Amp-Original-Verdict: FILE UNKNOWN X-Amp-File-Uploaded: False Received: from fmsmga007.fm.intel.com ([10.253.24.52]) by fmsmga106.fm.intel.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 12 Sep 2019 18:54:04 -0700 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.64,499,1559545200"; d="scan'208";a="186304831" Received: from sjchrist-coffee.jf.intel.com (HELO linux.intel.com) ([10.54.74.41]) by fmsmga007.fm.intel.com with ESMTP; 12 Sep 2019 18:54:03 -0700 Date: Thu, 12 Sep 2019 18:54:03 -0700 From: Sean Christopherson To: Paolo Bonzini , Radim =?utf-8?B?S3LEjW3DocWZ?= Cc: Vitaly Kuznetsov , Wanpeng Li , Jim Mattson , Joerg Roedel , kvm@vger.kernel.org, linux-kernel@vger.kernel.org, Fuqian Huang Subject: Re: [PATCH] KVM: x86: Handle unexpected MMIO accesses using master abort semantics Message-ID: <20190913015403.GB6588@linux.intel.com> References: <20190912235603.18954-1-sean.j.christopherson@intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190912235603.18954-1-sean.j.christopherson@intel.com> User-Agent: Mutt/1.5.24 (2015-08-30) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Sep 12, 2019 at 04:56:03PM -0700, Sean Christopherson wrote: > Use master abort semantics, i.e. reads return all ones and writes are > dropped, to handle unexpected MMIO accesses when reading guest memory > instead of returning X86EMUL_IO_NEEDED, which in turn gets interpreted > as a guest page fault. > > Emulation of certain instructions, notably VMX instructions, involves > reading or writing guest memory without going through the emulator. > These emulation flows are not equipped to handle MMIO accesses as no > sane and properly functioning guest kernel will target MMIO with such > instructions, and so simply inject a page fault in response to > X86EMUL_IO_NEEDED. > > While not 100% correct, using master abort semantics is at least > sometimes correct, e.g. non-existent MMIO accesses do actually master > abort, whereas injecting a page fault is always wrong, i.e. the issue > lies in the physical address domain, not in the virtual to physical > translation. > > Apply the logic to kvm_write_guest_virt_system() in addition to > replacing existing #PF logic in kvm_read_guest_virt(), as VMPTRST uses > the former, i.e. can also leak a host stack address. > > Reported-by: Fuqian Huang > Cc: stable@vger.kernel.org > Signed-off-by: Sean Christopherson > --- > arch/x86/kvm/x86.c | 40 +++++++++++++++++++++++++++++++--------- > 1 file changed, 31 insertions(+), 9 deletions(-) > > diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c > index b4cfd786d0b6..d1d7e9fac17a 100644 > --- a/arch/x86/kvm/x86.c > +++ b/arch/x86/kvm/x86.c > @@ -5234,16 +5234,24 @@ int kvm_read_guest_virt(struct kvm_vcpu *vcpu, > struct x86_exception *exception) > { > u32 access = (kvm_x86_ops->get_cpl(vcpu) == 3) ? PFERR_USER_MASK : 0; > + int r; > + > + r = kvm_read_guest_virt_helper(addr, val, bytes, vcpu, access, > + exception); > > /* > - * FIXME: this should call handle_emulation_failure if X86EMUL_IO_NEEDED > - * is returned, but our callers are not ready for that and they blindly > - * call kvm_inject_page_fault. Ensure that they at least do not leak > - * uninitialized kernel stack memory into cr2 and error code. > + * FIXME: this should technically call out to userspace to handle the > + * MMIO access, but our callers are not ready for that, so emulate > + * master abort behavior instead, i.e. writes are dropped. Dagnabbit, fixed this to make it 'reads return all ones' and forgot to commit.. v2 on its way. > */ > - memset(exception, 0, sizeof(*exception)); > - return kvm_read_guest_virt_helper(addr, val, bytes, vcpu, access, > - exception); > + if (r == X86EMUL_IO_NEEDED) { > + memset(val, 0xff, bytes); > + return 0; > + } > + if (r == X86EMUL_PROPAGATE_FAULT) > + return -EFAULT; > + WARN_ON_ONCE(r); > + return 0; > } > EXPORT_SYMBOL_GPL(kvm_read_guest_virt); > > @@ -5317,11 +5325,25 @@ static int emulator_write_std(struct x86_emulate_ctxt *ctxt, gva_t addr, void *v > int kvm_write_guest_virt_system(struct kvm_vcpu *vcpu, gva_t addr, void *val, > unsigned int bytes, struct x86_exception *exception) > { > + int r; > + > /* kvm_write_guest_virt_system can pull in tons of pages. */ > vcpu->arch.l1tf_flush_l1d = true; > > - return kvm_write_guest_virt_helper(addr, val, bytes, vcpu, > - PFERR_WRITE_MASK, exception); > + r = kvm_write_guest_virt_helper(addr, val, bytes, vcpu, > + PFERR_WRITE_MASK, exception); > + > + /* > + * FIXME: this should technically call out to userspace to handle the > + * MMIO access, but our callers are not ready for that, so emulate > + * master abort behavior instead, i.e. writes are dropped. > + */ > + if (r == X86EMUL_IO_NEEDED) > + return 0; > + if (r == X86EMUL_PROPAGATE_FAULT) > + return -EFAULT; > + WARN_ON_ONCE(r); > + return 0; > } > EXPORT_SYMBOL_GPL(kvm_write_guest_virt_system); > > -- > 2.22.0 >