From mboxrd@z Thu Jan 1 00:00:00 1970 From: Will Deacon Subject: Re: [PATCH v2] iommu/arm-smmu: Break insecure users by disabling bypass by default Date: Thu, 4 Apr 2019 16:00:05 +0100 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 Return-path: Content-Disposition: inline In-Reply-To: <20190301192017.39770-1-dianders@chromium.org> Sender: linux-kernel-owner@vger.kernel.org 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 List-Id: linux-arm-msm@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