From patchwork Mon Apr 4 15:46:22 2016 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Andy Lutomirski X-Patchwork-Id: 8742001 Return-Path: X-Original-To: patchwork-xen-devel@patchwork.kernel.org Delivered-To: patchwork-parsemail@patchwork2.web.kernel.org Received: from mail.kernel.org (mail.kernel.org [198.145.29.136]) by patchwork2.web.kernel.org (Postfix) with ESMTP id 3E704C0553 for ; Mon, 4 Apr 2016 15:48:31 +0000 (UTC) Received: from mail.kernel.org (localhost [127.0.0.1]) by mail.kernel.org (Postfix) with ESMTP id 68EDD2025A for ; Mon, 4 Apr 2016 15:48:30 +0000 (UTC) Received: from lists.xenproject.org (lists.xenproject.org [192.237.175.120]) (using TLSv1.2 with cipher AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 8D86820204 for ; Mon, 4 Apr 2016 15:48:29 +0000 (UTC) Received: from localhost ([127.0.0.1] helo=lists.xenproject.org) by lists.xenproject.org with esmtp (Exim 4.84_2) (envelope-from ) id 1an6hy-0001eG-AE; Mon, 04 Apr 2016 15:46:30 +0000 Received: from mail6.bemta14.messagelabs.com ([193.109.254.103]) by lists.xenproject.org with esmtp (Exim 4.84_2) (envelope-from ) id 1an6hx-0001e5-AI for Xen-devel@lists.xen.org; Mon, 04 Apr 2016 15:46:29 +0000 Received: from [193.109.254.147] by server-6.bemta-14.messagelabs.com id D3/95-03497-45C82075; Mon, 04 Apr 2016 15:46:28 +0000 X-Brightmail-Tracker: H4sIAAAAAAAAA+NgFnrHLMWRWlGSWpSXmKPExsVybKJsh25wD1O 4wdfZlhZLPi5mcWD0OLr7N1MAYxRrZl5SfkUCa8aKZXMZC/o5K64+2MjawLibvYuRi0NIYCqj xNIlU9kgnAlMEvemfQTKcHCwCahLtHT6djFycogISEvMfraPFcRmFmhilpizUg7EFhbwkpi6/ hs7iM0ioCpxZ9U3ZhCbVyBU4sjlWWC2hICcxLYtexgh7AyJeT1zWCFsL4lFNy5B2WoSV89tYp 7AyLOAkWEVo0ZxalFZapGuoYleUlFmekZJbmJmjq4hkJubWlycmJ6ak5hUrJecn7uJEej3egY Gxh2M3097HmKU5GBSEuV1r2IKF+JLyk+pzEgszogvKs1JLT7EKMPBoSTB+7ALKCdYlJqeWpGW mQMMQJi0BAePkgivQTdQmre4IDG3ODMdInWKUZejZdOdtUxCLHn5ealS4rxPQGYIgBRllObBj YBFwyVGWSlhXkYGBgYhnoLUotzMElT5V4ziHIxKwrxlIKt4MvNK4Da9AjqCCeiIemGwI0oSEV JSDYyhrLx7bpg0F3ApKpx36bFJ3yP95vpji18zfyUvcM9+5fB9zsY12y49c8q8I/RKzq9g5YF 6mz3+xz2qW/PfqZl5iuybo+Fhef/vaoeNveZMMif5j3C3Tih9PafxRiNrtv3Sp7uTGf8bbudz U9i3TKTPp7fH8ztT2vwfWzTU0/aXCPZObF2pFKzEUpyRaKjFXFScCAAmYyROgQIAAA== X-Env-Sender: luto@kernel.org X-Msg-Ref: server-3.tower-27.messagelabs.com!1459784786!35212456!1 X-Originating-IP: [198.145.29.136] X-SpamReason: No, hits=0.5 required=7.0 tests=BODY_RANDOM_LONG X-StarScan-Received: X-StarScan-Version: 8.28; banners=-,-,- X-VirusChecked: Checked Received: (qmail 25773 invoked from network); 4 Apr 2016 15:46:27 -0000 Received: from mail.kernel.org (HELO mail.kernel.org) (198.145.29.136) by server-3.tower-27.messagelabs.com with DHE-RSA-AES256-GCM-SHA384 encrypted SMTP; 4 Apr 2016 15:46:27 -0000 Received: from mail.kernel.org (localhost [127.0.0.1]) by mail.kernel.org (Postfix) with ESMTP id 280E42024F; Mon, 4 Apr 2016 15:46:25 +0000 (UTC) Received: from localhost (c-71-202-137-17.hsd1.ca.comcast.net [71.202.137.17]) (using TLSv1.2 with cipher AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 6326E20204; Mon, 4 Apr 2016 15:46:24 +0000 (UTC) From: Andy Lutomirski To: X86 ML Date: Mon, 4 Apr 2016 08:46:22 -0700 Message-Id: <5f1dcd6919f4a5923959a8065cb2c04d9dac1412.1459784772.git.luto@kernel.org> X-Mailer: git-send-email 2.5.5 X-Spam-Status: No, score=-4.2 required=5.0 tests=BAYES_00, RCVD_IN_DNSWL_MED, UNPARSEABLE_RELAY autolearn=unavailable version=3.3.1 X-Spam-Checker-Version: SpamAssassin 3.3.1 (2010-03-16) on mail.kernel.org X-Virus-Scanned: ClamAV using ClamSMTP Cc: KVM list , Peter Zijlstra , Linus Torvalds , linux-kernel@vger.kernel.org, xen-devel , Borislav Petkov , Andy Lutomirski , Paolo Bonzini , Andrew Morton , Arjan van de Ven Subject: [Xen-devel] [PATCH] x86/extable: Add a comment about early exception handlers X-BeenThere: xen-devel@lists.xen.org X-Mailman-Version: 2.1.18 Precedence: list List-Id: Xen developer discussion List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , MIME-Version: 1.0 Errors-To: xen-devel-bounces@lists.xen.org Sender: "Xen-devel" X-Virus-Scanned: ClamAV using ClamSMTP Borislav asked for a comment explaining why all exception handlers are allowed early. Signed-off-by: Andy Lutomirski Reviewed-by: Borislav Petkov --- arch/x86/mm/extable.c | 14 ++++++++++++++ 1 file changed, 14 insertions(+) diff --git a/arch/x86/mm/extable.c b/arch/x86/mm/extable.c index 98b5f45d9d79..36fe03bc81ee 100644 --- a/arch/x86/mm/extable.c +++ b/arch/x86/mm/extable.c @@ -132,6 +132,20 @@ void __init early_fixup_exception(struct pt_regs *regs, int trapnr) if (regs->cs != __KERNEL_CS) goto fail; + /* + * The full exception fixup machinery is available as soon as + * the early IDT is loaded. This means that it is the + * responsibility of extable users to either function correctly + * when handlers are invoked early or to simply avoid causing + * exceptions before they're ready to handle them. + * + * This is better than filtering which handlers can be used, + * because refusing to call a handler here is guaranteed to + * result in a hard-to-debug panic. + * + * Keep in mind that not all vectors actually get here. Early + * fage faults, for example, are special. + */ if (fixup_exception(regs, trapnr)) return;