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Date: Thu, 4 Apr 2019 16:00:05 +0100
From: Will Deacon <will.deacon@....com>
To: Douglas Anderson <dianders@...omium.org>
Cc: Joerg Roedel <joro@...tes.org>,
Robin Murphy <robin.murphy@....com>,
linux-arm-msm@...r.kernel.org,
Vivek Gautam <vivek.gautam@...eaurora.org>,
Rob Clark <robdclark@...il.com>, evgreen@...omium.org,
tfiga@...omium.org, linux-kernel@...r.kernel.org,
iommu@...ts.linux-foundation.org,
linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH v2] iommu/arm-smmu: Break insecure users by disabling
bypass by default
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 <robin.murphy@....com>
> Signed-off-by: Douglas Anderson <dianders@...omium.org>
> ---
>
> 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
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