linux-kernel - Re: [PATCH v4] drm/virtio: Add option to disable KMS support

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Date:   Wed, 1 Mar 2023 03:37:24 +0300
From:   Dmitry Osipenko <dmitry.osipenko@...labora.com>
To:     Gerd Hoffmann <kraxel@...hat.com>
Cc:     Chia-I Wu <olvaffe@...il.com>, Ryan Neph <ryanneph@...omium.org>,
        Daniel Vetter <daniel@...ll.ch>,
        Rob Clark <robdclark@...il.com>,
        Rob Clark <robdclark@...omium.org>,
        dri-devel@...ts.freedesktop.org, David Airlie <airlied@...hat.com>,
        Gurchetan Singh <gurchetansingh@...omium.org>,
        "open list:VIRTIO GPU DRIVER" 
        <virtualization@...ts.linux-foundation.org>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v4] drm/virtio: Add option to disable KMS support

On 2/28/23 18:54, Rob Clark wrote:
> From: Rob Clark <robdclark@...omium.org>
> 
> Add a build option to disable modesetting support.  This is useful in
> cases where the guest only needs to use the GPU in a headless mode, or
> (such as in the CrOS usage) window surfaces are proxied to a host
> compositor.
> 
> As the modesetting ioctls are a big surface area for potential security
> bugs to be found (it's happened in the past, we should assume it will
> again in the future), it makes sense to have a build option to disable
> those ioctls in cases where they serve no legitimate purpose.
> 
> v2: Use more if (IS_ENABLED(...))
> v3: Also permit the host to advertise no scanouts
> v4: Spiff out commit msg
> 
> Signed-off-by: Rob Clark <robdclark@...omium.org>
> Reviewed-by: Dmitry Osipenko <dmitry.osipenko@...labora.com>
> ---

Gerd, to give you some context on the v4.. we've chatted a bit more on
the #dri-devel and concluded that config option is the most robust way
of having KMS disabled from a security stand point. We would also want
to have a per-driver option (and not global) because there are scenarios
of using passthrough GPU + virtio-gpu in a guest, hence we would only
want to toggle KMS for a particular driver.

-- 
Best regards,
Dmitry