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=-5.5 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_PASS,USER_AGENT_MUTT 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 E9EF0C4360F for ; Thu, 4 Apr 2019 15:00:18 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id B8EC42064A for ; Thu, 4 Apr 2019 15:00:18 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729067AbfDDPAR (ORCPT ); Thu, 4 Apr 2019 11:00:17 -0400 Received: from usa-sjc-mx-foss1.foss.arm.com ([217.140.101.70]:33732 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726942AbfDDPAR (ORCPT ); Thu, 4 Apr 2019 11:00:17 -0400 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 809B9169E; Thu, 4 Apr 2019 08:00:16 -0700 (PDT) Received: from fuggles.cambridge.arm.com (usa-sjc-imap-foss1.foss.arm.com [10.72.51.249]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 8F8753F59C; Thu, 4 Apr 2019 08:00:14 -0700 (PDT) Date: Thu, 4 Apr 2019 16:00:05 +0100 From: Will Deacon To: Douglas Anderson Cc: Joerg Roedel , Robin Murphy , linux-arm-msm@vger.kernel.org, Vivek Gautam , Rob Clark , evgreen@chromium.org, tfiga@chromium.org, linux-kernel@vger.kernel.org, iommu@lists.linux-foundation.org, linux-arm-kernel@lists.infradead.org Subject: Re: [PATCH v2] iommu/arm-smmu: Break insecure users by disabling bypass by default Message-ID: <20190404145957.GA25912@fuggles.cambridge.arm.com> References: <20190301192017.39770-1-dianders@chromium.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190301192017.39770-1-dianders@chromium.org> User-Agent: Mutt/1.11.1+86 (6f28e57d73f2) () Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Mar 01, 2019 at 11:20:17AM -0800, Douglas Anderson wrote: > If you're bisecting why your peripherals stopped working, it's > probably this CL. Specifically if you see this in your dmesg: > Unexpected global fault, this could be serious > ...then it's almost certainly this CL. > > Running your IOMMU-enabled peripherals with the IOMMU in bypass mode > is insecure and effectively disables the protection they provide. > There are few reasons to allow unmatched stream bypass, and even fewer > good ones. > > This patch starts the transition over to make it much harder to run > your system insecurely. Expected steps: > > 1. By default disable bypass (so anyone insecure will notice) but make > it easy for someone to re-enable bypass with just a KConfig change. > That's this patch. > > 2. After people have had a little time to come to grips with the fact > that they need to set their IOMMUs properly and have had time to > dig into how to do this, the KConfig will be eliminated and bypass > will simply be disabled. Folks who are truly upset and still > haven't fixed their system can either figure out how to add > 'arm-smmu.disable_bypass=n' to their command line or revert the > patch in their own private kernel. Of course these folks will be > less secure. > > Suggested-by: Robin Murphy > Signed-off-by: Douglas Anderson > --- > > Changes in v2: > - Flipped default to 'yes' and changed comments a lot. > > drivers/iommu/Kconfig | 25 +++++++++++++++++++++++++ > drivers/iommu/arm-smmu.c | 3 ++- > 2 files changed, 27 insertions(+), 1 deletion(-) Cheers, I'll pick this one up for 5.2. Will