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=-0.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS,URIBL_BLOCKED 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 9E1DAECDFB1 for ; Fri, 13 Jul 2018 17:11:00 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 55D45208B0 for ; Fri, 13 Jul 2018 17:11:00 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 55D45208B0 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1731552AbeGMR02 (ORCPT ); Fri, 13 Jul 2018 13:26:28 -0400 Received: from mx3-rdu2.redhat.com ([66.187.233.73]:35456 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1729622AbeGMR02 (ORCPT ); Fri, 13 Jul 2018 13:26:28 -0400 Received: from smtp.corp.redhat.com (int-mx05.intmail.prod.int.rdu2.redhat.com [10.11.54.5]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 4FA5C7DAC8; Fri, 13 Jul 2018 17:10:57 +0000 (UTC) Received: from vitty.brq.redhat.com.redhat.com (unknown [10.43.2.155]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 9D6A61C67B; Fri, 13 Jul 2018 17:10:55 +0000 (UTC) From: Vitaly Kuznetsov To: Sean Christopherson Cc: kvm@vger.kernel.org, Paolo Bonzini , Radim =?utf-8?B?S3LEjW3DocWZ?= , x86@kernel.org, Andy Lutomirski , "Dmitry V . Levin" , Masatake YAMATO , linux-kernel@vger.kernel.org Subject: Re: [PATCH] x86/kvm/vmx: don't read current->thread.{fs,gs}base of legacy tasks References: <20180711173718.8850-1-vkuznets@redhat.com> <20180713164650.GA14830@linux.intel.com> Date: Fri, 13 Jul 2018 19:10:54 +0200 In-Reply-To: <20180713164650.GA14830@linux.intel.com> (Sean Christopherson's message of "Fri, 13 Jul 2018 09:46:50 -0700") Message-ID: <87lgafvz6p.fsf@vitty.brq.redhat.com> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/25.3 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain X-Scanned-By: MIMEDefang 2.79 on 10.11.54.5 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.11.55.2]); Fri, 13 Jul 2018 17:10:57 +0000 (UTC) X-Greylist: inspected by milter-greylist-4.5.16 (mx1.redhat.com [10.11.55.2]); Fri, 13 Jul 2018 17:10:57 +0000 (UTC) for IP:'10.11.54.5' DOMAIN:'int-mx05.intmail.prod.int.rdu2.redhat.com' HELO:'smtp.corp.redhat.com' FROM:'vkuznets@redhat.com' RCPT:'' Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Sean Christopherson writes: > On Wed, Jul 11, 2018 at 07:37:18PM +0200, Vitaly Kuznetsov wrote: >> When we switched from doing rdmsr() to reading FS/GS base values from >> current->thread we completely forgot about legacy 32-bit userspaces which >> we still support in KVM (why?). task->thread.{fsbase,gsbase} are only >> synced for 64-bit processes, calling save_fsgs_for_kvm() and using >> its result from current is illegal for legacy processes. >> >> There's no ARCH_SET_FS/GS prctls for legacy applications. Base MSRs are, >> however, not always equal to zero. Intel's manual says (3.4.4 Segment >> Loading Instructions in IA-32e Mode): >> >> "In order to set up compatibility mode for an application, segment-load >> instructions (MOV to Sreg, POP Sreg) work normally in 64-bit mode. An >> entry is read from the system descriptor table (GDT or LDT) and is loaded >> in the hidden portion of the segment register. >> ... >> The hidden descriptor register fields for FS.base and GS.base are >> physically mapped to MSRs in order to load all address bits supported by >> a 64-bit implementation. >> " >> >> The issue was found by strace test suite where 32-bit ioctl_kvm_run test >> started segfaulting. >> >> Reported-by: Dmitry V. Levin >> Bisected-by: Masatake YAMATO >> Fixes: 42b933b59721 ("x86/kvm/vmx: read MSR_{FS,KERNEL_GS}_BASE from current->thread") >> Signed-off-by: Vitaly Kuznetsov >> --- >> arch/x86/kvm/vmx.c | 25 +++++++++++++++++-------- >> 1 file changed, 17 insertions(+), 8 deletions(-) >> >> diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c >> index 559a12b6184d..65968649b365 100644 >> --- a/arch/x86/kvm/vmx.c >> +++ b/arch/x86/kvm/vmx.c >> @@ -2560,6 +2560,7 @@ static void vmx_save_host_state(struct kvm_vcpu *vcpu) >> struct vcpu_vmx *vmx = to_vmx(vcpu); >> #ifdef CONFIG_X86_64 >> int cpu = raw_smp_processor_id(); >> + unsigned long fsbase, kernel_gsbase; > > Because bikeshedding is fun, what do you think about using fs_base and > kernel_gs_base for these names? I have a series that touches this > code and also adds local variables for {FS,GS}.base and {FS,GS}.sel. > I used {fs,gs}_base and {fs,gs}_sel to be consistent with the > vmx->host_state nomenclature (the local variables are used to update > the associated vmx->host_state variables), but I'll change my patches > if you have a strong preference for omitting the underscore. > I have nothing against underscores :-) Hope this small change can be done by Paolo/Radim upon commit. Or I'll send v2 if needed. -- Vitaly