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 Received: from phobos.denx.de (phobos.denx.de [85.214.62.61]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id B14EDC35274 for ; Mon, 18 Dec 2023 16:59:35 +0000 (UTC) Received: from h2850616.stratoserver.net (localhost [IPv6:::1]) by phobos.denx.de (Postfix) with ESMTP id BC6768718A; Mon, 18 Dec 2023 17:59:23 +0100 (CET) Authentication-Results: phobos.denx.de; dmarc=fail (p=none dis=none) header.from=arm.com Authentication-Results: phobos.denx.de; spf=pass smtp.mailfrom=u-boot-bounces@lists.denx.de Received: by phobos.denx.de (Postfix, from userid 109) id BA7DE8718A; Mon, 18 Dec 2023 17:59:22 +0100 (CET) Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by phobos.denx.de (Postfix) with ESMTP id 6C989870D4 for ; Mon, 18 Dec 2023 17:59:18 +0100 (CET) Authentication-Results: phobos.denx.de; dmarc=fail (p=none dis=none) header.from=arm.com Authentication-Results: phobos.denx.de; spf=pass smtp.mailfrom=abdellatif.elkhlifi@arm.com Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 9775C2F4; Mon, 18 Dec 2023 09:00:01 -0800 (PST) Received: from e130802.arm.com (unknown [10.57.4.48]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 514FF3F5A1; Mon, 18 Dec 2023 08:59:15 -0800 (PST) Date: Mon, 18 Dec 2023 16:59:09 +0000 From: Abdellatif El Khlifi To: Ilias Apalodimas Cc: xypron.glpk@gmx.de, sjg@chromium.org, mark.kettenis@xs4all.nl, Drew.Reed@arm.com, u-boot@lists.denx.de, nd@arm.com Subject: Re: Adding EFI runtime support to the Arm's FF-A bus Message-ID: <20231218165909.GA313366@e130802.arm.com> References: <20231214155346.GB295924@e130802.arm.com> <87ttok689d.fsf@bloch.sibelius.xs4all.nl> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: X-BeenThere: u-boot@lists.denx.de X-Mailman-Version: 2.1.39 Precedence: list List-Id: U-Boot discussion List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: u-boot-bounces@lists.denx.de Sender: "U-Boot" X-Virus-Scanned: clamav-milter 0.103.8 at phobos.denx.de X-Virus-Status: Clean Hi Ilias On Thu, Dec 14, 2023 at 09:47:13PM +0200, Ilias Apalodimas wrote: > Hi Mark, Abdellatif > > On Thu, 14 Dec 2023 at 18:47, Mark Kettenis wrote: > > > > > Date: Thu, 14 Dec 2023 15:53:46 +0000 > > > From: Abdellatif El Khlifi > > > > Hi Abdellatif, > > > > > Hi guys, > > > > > > I'd like to ask for advice regarding adding EFI RT support to the Arm's FF-A bus > > > in U-Boot. > > > > > > The objective is to enable the FF-A messaging APIs in EFI RT to be > > > used for comms with the secure world. This will help getting/setting > > > EFI variables through FF-A. > > > > > > The existing FF-A APIs in U-Boot call the DM APIs (which are not available at RT). > > > > > > Two possible solutions: > > > > > > 1/ having the entire U-Boot in RT space (as Simon stated in this discussion[1]) > > > > I don't think this is a terribly good idea. With this approach orders > > of magnitude more code will be present in kernel address space one the > > OS kernel is running and calling into the EFI runtime. Including code > > that may access hardware devices that are now under OS control. It > > will be nigh impossible to audit all that code and make sure that only > > a safe subset of it gets called. So... > > +100 > I think we should draw a line here. I mentioned it on another thread, > but I did a shot BoF in Plumbers discussing issues like this, > problems, and potential solutions [0] [1]. Since that talk patches for > the kernel that 'solve' the problem for RPMBs got pulled into > linux-next [2]. I watched your talk. Great work, thanks :) > The TL;DR of that talk is that if the kernel ends up being in control > of the hardware that stores the EFI variables, we need to find elegant > ways to teach the kernel how to store those directly. The EFI > requirement of an isolated flash is something that mostly came from > the x86 world and is not a reality on the majority of embedded boards. > I also think we should give up on Authenticated EFI variables in that > case. We get zero guarantees unless the medium has similar properties > to an RPMB. > If a vendor cares about proper UEFI secure boot he can implement > proper hardware. > > > > > > > > > 2/ Create an RT variant for the FF-A APIs needed. > > > These RT variant don't call the DM APIs > > > (e.g: ffa_mm_communicate_runtime, ffa_sync_send_receive_runtime, ...) > > > > > > What do you recommend please ? > > > > ...this is what I would recommend. Preferably in a way that refactors > > the code such that the low-level functionality is shared between the > > DM and non-DM APIs. > > Yes. The only thing you need to keep alive is the machinery to talk to > the secure world. The bus, flash driver etc should all be running > isolated in there. In that case you can implement SetVariableRT as > described the the EFI spec. Cool, thanks. That's my preferred solution too. mm_communicate() should be able to detect runtime mode so it calls ffa_mm_communicate_runtime(). Is there a way to check whether we are in EFI runtime or not ? Suggested changes (pseudo-code): __efi_runtime mm_communicate () { #if CONFIG_IS_ENABLED(ARM_FFA_TRANSPORT) if (RT) { /* NEW */         ret = ffa_mm_communicate_runtime(comm_buf, dsize); /* NEW */ } else {     mm_comms = get_mm_comms();     if (mm_comms == MM_COMMS_FFA)         ret = ffa_mm_communicate(comm_buf, dsize);     else         ret = optee_mm_communicate(comm_buf, dsize); } #else ... #endif Existing code: https://github.com/u-boot/u-boot/blob/master/lib/efi_loader/efi_variable_tee.c#L417 Cheers, Abdellatif