linux-kernel - Re: [PATCH 13/13] vfio/type1: Mark follow

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Message-ID: <20201007184705.GY5177@ziepe.ca>
Date:   Wed, 7 Oct 2020 15:47:05 -0300
From:   Jason Gunthorpe <jgg@...pe.ca>
To:     Daniel Vetter <daniel.vetter@...ll.ch>
Cc:     DRI Development <dri-devel@...ts.freedesktop.org>,
        LKML <linux-kernel@...r.kernel.org>, kvm@...r.kernel.org,
        Linux MM <linux-mm@...ck.org>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        linux-samsung-soc <linux-samsung-soc@...r.kernel.org>,
        "open list:DMA BUFFER SHARING FRAMEWORK" 
        <linux-media@...r.kernel.org>, linux-s390@...r.kernel.org,
        Daniel Vetter <daniel.vetter@...el.com>,
        Kees Cook <keescook@...omium.org>,
        Dan Williams <dan.j.williams@...el.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        John Hubbard <jhubbard@...dia.com>,
        Jérôme Glisse <jglisse@...hat.com>,
        Jan Kara <jack@...e.cz>,
        Alex Williamson <alex.williamson@...hat.com>,
        Cornelia Huck <cohuck@...hat.com>
Subject: Re: [PATCH 13/13] vfio/type1: Mark follow_pfn as unsafe

On Wed, Oct 07, 2020 at 08:14:06PM +0200, Daniel Vetter wrote:

> Hm, but wouldn't need that the semi-nasty vma_open trick to make sure
> that vma doesn't untimely disappear? Or is the idea to look up the
> underlying vfio object, and refcount that directly?

Ah, the patches Alex was working on had the refcount I think, it does
need co-ordination across multiple VFIO instances IIRC.

At least a simple check would guarentee we only have exposed PCI BAR
pages which is not as bad security wise as the other stuff.

Jason