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=-0.9 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 870C1C04EB8 for ; Mon, 10 Dec 2018 20:13:11 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 435262082F for ; Mon, 10 Dec 2018 20:13:11 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 435262082F Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=arm.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 S1728825AbeLJUNJ (ORCPT ); Mon, 10 Dec 2018 15:13:09 -0500 Received: from usa-sjc-mx-foss1.foss.arm.com ([217.140.101.70]:33962 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726607AbeLJUNJ (ORCPT ); Mon, 10 Dec 2018 15:13:09 -0500 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.72.51.249]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id D2C72EBD; Mon, 10 Dec 2018 12:13:08 -0800 (PST) Received: from [10.1.197.21] (usa-sjc-imap-foss1.foss.arm.com [10.72.51.249]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 2D1CA3F59C; Mon, 10 Dec 2018 12:12:56 -0800 (PST) Subject: Re: [PATCH v6 04/13] arm64/kvm: hide ptrauth from guests To: Richard Henderson Cc: linux-arm-kernel@lists.infradead.org, Adam Wallis , Amit Kachhap , Andrew Jones , Ard Biesheuvel , Catalin Marinas , Christoffer Dall , Cyrill Gorcunov , Dave P Martin , Jacob Bramley , Kees Cook , Marc Zyngier , Mark Rutland , Ramana Radhakrishnan , Suzuki K Poulose , Will Deacon , kvmarm@lists.cs.columbia.edu, linux-kernel@vger.kernel.org References: <20181207183931.4285-1-kristina.martsenko@arm.com> <20181207183931.4285-5-kristina.martsenko@arm.com> <57966497-d21c-5439-e4ba-d75f5552282f@linaro.org> From: Kristina Martsenko Message-ID: Date: Mon, 10 Dec 2018 20:12:54 +0000 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.3.0 MIME-Version: 1.0 In-Reply-To: <57966497-d21c-5439-e4ba-d75f5552282f@linaro.org> 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 On 09/12/2018 14:53, Richard Henderson wrote: > On 12/7/18 12:39 PM, Kristina Martsenko wrote: >> From: Mark Rutland >> >> In subsequent patches we're going to expose ptrauth to the host kernel >> and userspace, but things are a bit trickier for guest kernels. For the >> time being, let's hide ptrauth from KVM guests. >> >> Regardless of how well-behaved the guest kernel is, guest userspace >> could attempt to use ptrauth instructions, triggering a trap to EL2, >> resulting in noise from kvm_handle_unknown_ec(). So let's write up a >> handler for the PAC trap, which silently injects an UNDEF into the >> guest, as if the feature were really missing. > > Reviewing the long thread that accompanied v5, I thought we were *not* going to > trap PAuth instructions from the guest. > > In particular, the OS distribution may legitimately be built to include > hint-space nops. This includes XPACLRI, which is used by the C++ exception > unwinder and not controlled by SCTLR_EL1.EnI{A,B}. The plan was to disable trapping, yes. However, after that thread there was a retrospective change applied to the architecture, such that the XPACLRI (and XPACD/XPACI) instructions are no longer trapped by HCR_EL2.API. (The public documentation on this has not been updated yet.) This means that no HINT-space instructions should trap anymore. (The guest is expected to not set SCTLR_EL1.EnI{A,B} since ID_AA64ISAR1_EL1.{APA,API} read as 0.) > It seems like the header comment here, and Sorry, which header comment? >> +/* >> + * Guest usage of a ptrauth instruction (which the guest EL1 did not turn into >> + * a NOP). >> + */ >> +static int kvm_handle_ptrauth(struct kvm_vcpu *vcpu, struct kvm_run *run) >> + > > here, need updating. Changed it to "a trapped ptrauth instruction". Kristina