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 45196C352A3 for ; Tue, 11 Feb 2020 09:54:28 +0000 (UTC) Received: from mother.openwall.net (mother.openwall.net [195.42.179.200]) by mail.kernel.org (Postfix) with SMTP id 9773020842 for ; Tue, 11 Feb 2020 09:54:27 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=kernel.org header.i=@kernel.org header.b="wPuXWwxp" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 9773020842 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-17772-kernel-hardening=archiver.kernel.org@lists.openwall.com Received: (qmail 20372 invoked by uid 550); 11 Feb 2020 09:54:21 -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 20347 invoked from network); 11 Feb 2020 09:54:20 -0000 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1581414849; bh=dZ6CUij+Y34KbHJA5uYdVJiJ5KihU8UAFU+V7kMs+eE=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=wPuXWwxpf67WBRCSd6gmmbHXBuqvSvmM7CL5fmZPWW/D8lxpA6mBLOiyCCe82Ondo 3bLF5Mk0tp3wc7yciEiT9D+0q01TUCgH5co17XExIGf17qY4ndjc51TU5p8+1Z7yee ZmH+8o2VhBQKJpV1BsMvZ2mVsLoV5sPSz3ZIWmH4= Date: Tue, 11 Feb 2020 09:54:02 +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: <20200211095401.GA8560@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> <20200210182431.GC20840@lakrids.cambridge.arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200210182431.GC20840@lakrids.cambridge.arm.com> User-Agent: Mutt/1.10.1 (2018-07-13) On Mon, Feb 10, 2020 at 06:24:32PM +0000, Mark Rutland wrote: > On Mon, Feb 10, 2020 at 06:07:41PM +0000, 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? > > That covers the hyp->guest->hyp round trip, but not the host->hyp->host > portion surrounding that. Thanks, I missed that. It's annoying that we'll end up needing /both/ -ffixed-x18 *and* the save/restore around guest transitions, but if we actually want to use SCS for the VHE code then I see that it will be required. Sami -- can you restore -ffixed-x18 and then try the function attribute as suggested by James, please? Will