linux-kernel - Re: [PATCH 0/3] Apple M1 DART IOMMU driver

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Date:   Fri, 26 Mar 2021 21:03:32 +0100
From:   Arnd Bergmann <arnd@...nel.org>
To:     Mark Kettenis <mark.kettenis@...all.nl>
Cc:     sven@...npeter.dev, Rob Herring <robh@...nel.org>,
        "open list:IOMMU DRIVERS" <iommu@...ts.linux-foundation.org>,
        Joerg Roedel <joro@...tes.org>, Will Deacon <will@...nel.org>,
        Robin Murphy <robin.murphy@....com>,
        Hector Martin <marcan@...can.st>,
        Marc Zyngier <maz@...nel.org>,
        Mohamed Mediouni <mohamed.mediouni@...amail.com>,
        Stan Skowronek <stan@...ellium.com>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        DTML <devicetree@...r.kernel.org>
Subject: Re: [PATCH 0/3] Apple M1 DART IOMMU driver

On Fri, Mar 26, 2021 at 6:28 PM Mark Kettenis <mark.kettenis@...all.nl> wrote:

> I haven't figured out how the bypass stuff really works.  Corellium
> added support for it in their codebase when they added support for
> Thunderbolt, and some of the DARTs that seem to be related to
> Thunderbolt do indeed have a "bypass" property.  But it is unclear to
> me how the different puzzle pieces fit together for Thunderbolt.

As a general observation, bypass mode for Thunderbolt is what enabled
the http://thunderclap.io/ attack. This is extremely useful for debugging
a running kernel from another machine, but it's also something that
should never be done in a production kernel.

         Arnd