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=-9.8 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_GIT autolearn=unavailable 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 28558C3A5A2 for ; Fri, 23 Aug 2019 20:55:51 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 06F2F21848 for ; Fri, 23 Aug 2019 20:55:51 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2392958AbfHWUzq (ORCPT ); Fri, 23 Aug 2019 16:55:46 -0400 Received: from mga14.intel.com ([192.55.52.115]:48804 "EHLO mga14.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2392742AbfHWUzq (ORCPT ); Fri, 23 Aug 2019 16:55:46 -0400 X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False Received: from orsmga004.jf.intel.com ([10.7.209.38]) by fmsmga103.fm.intel.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 23 Aug 2019 13:55:45 -0700 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.64,422,1559545200"; d="scan'208";a="330833026" Received: from sjchrist-coffee.jf.intel.com ([10.54.74.41]) by orsmga004.jf.intel.com with ESMTP; 23 Aug 2019 13:55:45 -0700 From: Sean Christopherson To: Paolo Bonzini , =?UTF-8?q?Radim=20Kr=C4=8Dm=C3=A1=C5=99?= Cc: Sean Christopherson , Vitaly Kuznetsov , Wanpeng Li , Jim Mattson , Joerg Roedel , kvm@vger.kernel.org, linux-kernel@vger.kernel.org, Nadav Amit , Andy Lutomirski Subject: [PATCH] KVM: x86: Don't update RIP or do single-step on faulting emulation Date: Fri, 23 Aug 2019 13:55:44 -0700 Message-Id: <20190823205544.24052-1-sean.j.christopherson@intel.com> X-Mailer: git-send-email 2.22.0 MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Sender: kvm-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org Don't advance RIP or inject a single-step #DB if emulation signals a fault. This logic applies to all state updates that are conditional on clean retirement of the emulation instruction, e.g. updating RFLAGS was previously handled by commit 38827dbd3fb85 ("KVM: x86: Do not update EFLAGS on faulting emulation"). Not advancing RIP is likely a nop, i.e. ctxt->eip isn't updated with ctxt->_eip until emulation "retires" anyways. Skipping #DB injection fixes a bug reported by Andy Lutomirski where a #UD on SYSCALL due to invalid state with RFLAGS.RF=1 would loop indefinitely due to emulation overwriting the #UD with #DB and thus restarting the bad SYSCALL over and over. Cc: Nadav Amit Cc: stable@vger.kernel.org Reported-by: Andy Lutomirski Fixes: 663f4c61b803 ("KVM: x86: handle singlestep during emulation") Signed-off-by: Sean Christopherson --- Note, this has minor conflict with my recent series to cleanup the emulator return flows[*]. The end result should look something like: if (!ctxt->have_exception || exception_type(ctxt->exception.vector) == EXCPT_TRAP) { kvm_rip_write(vcpu, ctxt->eip); if (r && ctxt->tf) r = kvm_vcpu_do_singlestep(vcpu); __kvm_set_rflags(vcpu, ctxt->eflags); } [*] https://lkml.kernel.org/r/20190823010709.24879-1-sean.j.christopherson@intel.com arch/x86/kvm/x86.c | 9 +++++---- 1 file changed, 5 insertions(+), 4 deletions(-) diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index b4cfd786d0b6..d2962671c3d3 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -6611,12 +6611,13 @@ int x86_emulate_instruction(struct kvm_vcpu *vcpu, unsigned long rflags = kvm_x86_ops->get_rflags(vcpu); toggle_interruptibility(vcpu, ctxt->interruptibility); vcpu->arch.emulate_regs_need_sync_to_vcpu = false; - kvm_rip_write(vcpu, ctxt->eip); - if (r == EMULATE_DONE && ctxt->tf) - kvm_vcpu_do_singlestep(vcpu, &r); if (!ctxt->have_exception || - exception_type(ctxt->exception.vector) == EXCPT_TRAP) + exception_type(ctxt->exception.vector) == EXCPT_TRAP) { + kvm_rip_write(vcpu, ctxt->eip); + if (r == EMULATE_DONE && ctxt->tf) + kvm_vcpu_do_singlestep(vcpu, &r); __kvm_set_rflags(vcpu, ctxt->eflags); + } /* * For STI, interrupts are shadowed; so KVM_REQ_EVENT will -- 2.22.0