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=-2.6 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, USER_AGENT_SANE_1 autolearn=no 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 39AEAC35254 for ; Mon, 10 Feb 2020 18:07:49 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 0E18020863 for ; Mon, 10 Feb 2020 18:07:49 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1581358069; bh=fZY3SQNpPCnRBs32URTn+EedNYpwNvv58zAKZ4PXDQ8=; h=Date:From:To:Cc:Subject:References:In-Reply-To:List-ID:From; b=Jif6zuExtJ+1MhSQoKBdAEflOXJM1oUkl3uyau2gvmtfzwtyXy2bdhywfR8kpqxPv VJxoXJt+HljRC0yL5Ocw5mCjOKAndawjAllYZC9vYcciJ1KIsrxUDULPIgQcL4QRes i6uEeYHLqFCvdojLZuQGxMXnsAV0olXWx7sIFmSc= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727563AbgBJSHs (ORCPT ); Mon, 10 Feb 2020 13:07:48 -0500 Received: from mail.kernel.org ([198.145.29.99]:41900 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726809AbgBJSHs (ORCPT ); Mon, 10 Feb 2020 13:07:48 -0500 Received: from willie-the-truck (236.31.169.217.in-addr.arpa [217.169.31.236]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 527422082F; Mon, 10 Feb 2020 18:07:44 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1581358067; bh=fZY3SQNpPCnRBs32URTn+EedNYpwNvv58zAKZ4PXDQ8=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=MhSFm6pxgBM4UCGwR1shK5x3S7ghvaKBgaa8wHBuZU3zoh8GJXUvL//MSDY85r1eE BRup8cnQdmJ0sIk/2rKEK0dbZ6Wn1eVTFVkGNxHeHu64JFJ+BtEQ0wbQrrWPJEVlut 0ZjWRbmrsBXc1XHZTYJ/fzWCK3XhFd2c6j3rvmf8= Date: Mon, 10 Feb 2020 18:07:41 +0000 From: Will Deacon To: Mark Rutland Cc: James Morse , Sami Tolvanen , Catalin Marinas , Steven Rostedt , Masami Hiramatsu , Ard Biesheuvel , Dave Martin , Kees Cook , Laura Abbott , Marc Zyngier , Nick Desaulniers , Jann Horn , Miguel Ojeda , Masahiro Yamada , clang-built-linux@googlegroups.com, kernel-hardening@lists.openwall.com, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v7 09/11] arm64: disable SCS for hypervisor code Message-ID: <20200210180740.GA24354@willie-the-truck> References: <20191018161033.261971-1-samitolvanen@google.com> <20200128184934.77625-1-samitolvanen@google.com> <20200128184934.77625-10-samitolvanen@google.com> <6f62b3c0-e796-e91c-f53b-23bd80fcb065@arm.com> <20200210175214.GA23318@willie-the-truck> <20200210180327.GB20840@lakrids.cambridge.arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200210180327.GB20840@lakrids.cambridge.arm.com> User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Feb 10, 2020 at 06:03:28PM +0000, Mark Rutland wrote: > On Mon, Feb 10, 2020 at 05:52:15PM +0000, Will Deacon wrote: > > On Mon, Feb 10, 2020 at 05:18:58PM +0000, James Morse wrote: > > > On 28/01/2020 18:49, Sami Tolvanen wrote: > > > > Filter out CC_FLAGS_SCS and -ffixed-x18 for code that runs at a > > > > different exception level. > > > > > > Hmmm, there are two things being disabled here. > > > > > > Stashing the lr in memory pointed to by VA won't work transparently at EL2 ... but > > > shouldn't KVM's C code still treat x18 as a fixed register? > > > > My review of v6 suggested dropping the -ffixed-x18 as well, since it's only > > introduced by SCS (in patch 5) and so isn't required by anything else. Why > > do you think it's needed? > > When EL1 code calls up to hyp, it expects x18 to be preserved across the > call, so hyp needs to either preserve it explicitly across a transitions > from/to EL1 or always preserve it. I thought we explicitly saved/restored it across the call after af12376814a5 ("arm64: kvm: stop treating register x18 as caller save"). Is that not sufficient? > The latter is easiest since any code used by VHE hyp code will need x18 > saved anyway (ans so any common hyp code needs to). I would personally prefer to split the VHE and non-VHE code so they can be compiled with separate options. Will