linux-kernel - Re: [PATCH v5 11/15] PCI: Obey iomem restrictions for procfs mmap

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Date:   Tue, 3 Nov 2020 14:09:35 -0800
From:   Dan Williams <dan.j.williams@...el.com>
To:     Bjorn Helgaas <helgaas@...nel.org>
Cc:     Daniel Vetter <daniel.vetter@...ll.ch>,
        DRI Development <dri-devel@...ts.freedesktop.org>,
        LKML <linux-kernel@...r.kernel.org>,
        KVM list <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>,
        "Linux-media@...r.kernel.org" <linux-media@...r.kernel.org>,
        Daniel Vetter <daniel.vetter@...el.com>,
        Jason Gunthorpe <jgg@...pe.ca>,
        Kees Cook <keescook@...omium.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        John Hubbard <jhubbard@...dia.com>,
        Jérôme Glisse <jglisse@...hat.com>,
        Jan Kara <jack@...e.cz>, Bjorn Helgaas <bhelgaas@...gle.com>,
        Linux PCI <linux-pci@...r.kernel.org>
Subject: Re: [PATCH v5 11/15] PCI: Obey iomem restrictions for procfs mmap

On Tue, Nov 3, 2020 at 1:28 PM Bjorn Helgaas <helgaas@...nel.org> wrote:
>
> On Fri, Oct 30, 2020 at 11:08:11AM +0100, Daniel Vetter wrote:
> > There's three ways to access PCI BARs from userspace: /dev/mem, sysfs
> > files, and the old proc interface. Two check against
> > iomem_is_exclusive, proc never did. And with CONFIG_IO_STRICT_DEVMEM,
> > this starts to matter, since we don't want random userspace having
> > access to PCI BARs while a driver is loaded and using it.
> >
> > Fix this by adding the same iomem_is_exclusive() check we already have
> > on the sysfs side in pci_mmap_resource().
> >
> > References: 90a545e98126 ("restrict /dev/mem to idle io memory ranges")
> > Signed-off-by: Daniel Vetter <daniel.vetter@...el.com>
>
> This is OK with me but it looks like IORESOURCE_EXCLUSIVE is currently
> only used in a few places:
>
>   e1000_probe() calls pci_request_selected_regions_exclusive(),
>   ne_pci_probe() calls pci_request_regions_exclusive(),
>   vmbus_allocate_mmio() calls request_mem_region_exclusive()
>
> which raises the question of whether it's worth keeping
> IORESOURCE_EXCLUSIVE at all.  I'm totally fine with removing it
> completely.

Now that CONFIG_IO_STRICT_DEVMEM upgrades IORESOURCE_BUSY to
IORESOURCE_EXCLUSIVE semantics the latter has lost its meaning so I'd
be in favor of removing it as well.