linux-kernel - Re: [PATCH] vfio iommu type1: Bypass the vma permission check in vfio_pin_pages

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Message-ID: <20201125155711.GA6489@xz-x1>
Date:   Wed, 25 Nov 2020 10:57:11 -0500
From:   Peter Xu <peterx@...hat.com>
To:     Justin He <Justin.He@....com>
Cc:     Alex Williamson <alex.williamson@...hat.com>,
        Cornelia Huck <cohuck@...hat.com>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Stefan Hajnoczi <stefanha@...hat.com>
Subject: Re: [PATCH] vfio iommu type1: Bypass the vma permission check in
 vfio_pin_pages_remote()

On Wed, Nov 25, 2020 at 01:05:25AM +0000, Justin He wrote:
> > I'd appreciate if you could explain why vfio needs to dma map some
> > PROT_NONE
> 
> Virtiofs will map a PROT_NONE cache window region firstly, then remap the sub
> region of that cache window with read or write permission. I guess this might
> be an security concern. Just CC virtiofs expert Stefan to answer it more accurately.

Yep.  Since my previous sentence was cut off, I'll rephrase: I was thinking
whether qemu can do vfio maps only until it remaps the PROT_NONE regions into
PROT_READ|PROT_WRITE ones, rather than trying to map dma pages upon PROT_NONE.

Thanks,

-- 
Peter Xu