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=-5.3 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,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 F0AEDC43331 for ; Mon, 11 Nov 2019 14:32:49 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id D1516214E0 for ; Mon, 11 Nov 2019 14:32:49 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727050AbfKKOcs (ORCPT ); Mon, 11 Nov 2019 09:32:48 -0500 Received: from mx2.suse.de ([195.135.220.15]:42212 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1726832AbfKKOcs (ORCPT ); Mon, 11 Nov 2019 09:32:48 -0500 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.220.254]) by mx1.suse.de (Postfix) with ESMTP id DA89DACD8; Mon, 11 Nov 2019 14:32:46 +0000 (UTC) Subject: [PATCH 2/2] x86/Xen/32: simplify xen_iret_crit_fixup's ring check From: Jan Beulich To: Juergen Gross , Boris Ostrovsky Cc: lkml , the arch/x86 maintainers , "xen-devel@lists.xenproject.org" References: Message-ID: Date: Mon, 11 Nov 2019 15:32:59 +0100 User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:60.0) Gecko/20100101 Thunderbird/60.9.1 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org This can be had with two instead of six insns, by just checking the high CS.RPL bit. Also adjust the comment - there would be no #GP in the mentioned cases, as there's no segment limit violation or alike. Instead there'd be #PF, but that one reports the target EIP of said branch, not the address of the branch insn itself. Signed-off-by: Jan Beulich --- An alternative would be to keep using SEGMENT_RPL_MASK, but follow it with "jpe". --- a/arch/x86/xen/xen-asm_32.S +++ b/arch/x86/xen/xen-asm_32.S @@ -153,22 +153,15 @@ hyper_iret: * it's still on stack), we need to restore its value here. */ ENTRY(xen_iret_crit_fixup) - pushl %ecx /* * Paranoia: Make sure we're really coming from kernel space. * One could imagine a case where userspace jumps into the * critical range address, but just before the CPU delivers a - * GP, it decides to deliver an interrupt instead. Unlikely? - * Definitely. Easy to avoid? Yes. The Intel documents - * explicitly say that the reported EIP for a bad jump is the - * jump instruction itself, not the destination, but some - * virtual environments get this wrong. + * PF, it decides to deliver an interrupt instead. Unlikely? + * Definitely. Easy to avoid? Yes. */ - movl 3*4(%esp), %ecx /* nested CS */ - andl $SEGMENT_RPL_MASK, %ecx - cmpl $USER_RPL, %ecx - popl %ecx - je 2f + testb $2, 2*4(%esp) /* nested CS */ + jnz 2f /* * If eip is before iret_restore_end then stack