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 B52F8C3B187 for ; Tue, 11 Feb 2020 09:55:44 +0000 (UTC) Received: from mother.openwall.net (mother.openwall.net [195.42.179.200]) by mail.kernel.org (Postfix) with SMTP id 163C3214DB for ; Tue, 11 Feb 2020 09:55:43 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=kernel.org header.i=@kernel.org header.b="hrXJkcSk" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 163C3214DB Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=kernel.org Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=kernel-hardening-return-17773-kernel-hardening=archiver.kernel.org@lists.openwall.com Received: (qmail 22255 invoked by uid 550); 11 Feb 2020 09:55:38 -0000 Mailing-List: contact kernel-hardening-help@lists.openwall.com; run by ezmlm Precedence: bulk List-Post: List-Help: List-Unsubscribe: List-Subscribe: List-ID: Received: (qmail 22235 invoked from network); 11 Feb 2020 09:55:37 -0000 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1581414926; bh=q0Fz9yIHjMR47rqb63t0DZl1MM211pLUxeDAzl1/TSU=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=hrXJkcSkEoSoFke6H/bWzn+haEaMNsTni9NIh0NgD7P0mnftHNPZG2n/2stHF8MKF mUeshVt39Y4lYdMB5hiW9Q2LCA2kIHGnewOd1K85B0nChMIUWGAuZ249tThQJZU4P+ U/CFhsQ7s3AcDzue88/R8xKJUiKDB07ydtxZI/tI= Date: Tue, 11 Feb 2020 09:55:19 +0000 From: Will Deacon To: Marc Zyngier Cc: Mark Rutland , James Morse , Sami Tolvanen , Catalin Marinas , Steven Rostedt , Masami Hiramatsu , Ard Biesheuvel , Dave Martin , Kees Cook , Laura Abbott , 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: <20200211095519.GB8560@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> <20200210180740.GA24354@willie-the-truck> <43839239237869598b79cab90e100127@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <43839239237869598b79cab90e100127@kernel.org> User-Agent: Mutt/1.10.1 (2018-07-13) On Tue, Feb 11, 2020 at 09:14:52AM +0000, Marc Zyngier wrote: > On 2020-02-10 18:07, Will Deacon wrote: > > 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. > > This is going to generate a lot of code duplication (or at least object > duplication), > as the two code paths are intricately linked and splitting them to support > different > compilation options and/or calling conventions. > > I'm not fundamentally opposed to that, but it should come with ways to still > manage it as a unified code base as much as possible, as ways to discard the > unused part at runtime (which should become easy to do once we have two > distinct sets of objects). Agreed, and I don't want to hold up the SCS patches because of this. I'm just nervous about the function attribute because I've only ever had terrible experiences with them. Maybe it will work this time (!) Will