From: Bjorn Helgaas <email@example.com> To: Daniel Vetter <firstname.lastname@example.org> Cc: "Dan Williams" <email@example.com>, "DRI Development" <firstname.lastname@example.org>, LKML <email@example.com>, "KVM list" <firstname.lastname@example.org>, "Linux MM" <email@example.com>, "Linux ARM" <firstname.lastname@example.org>, linux-samsung-soc <email@example.com>, "Linuxfirstname.lastname@example.org" <email@example.com>, "Daniel Vetter" <firstname.lastname@example.org>, "Jason Gunthorpe" <email@example.com>, "Kees Cook" <firstname.lastname@example.org>, "Andrew Morton" <email@example.com>, "John Hubbard" <firstname.lastname@example.org>, "Jérôme Glisse" <email@example.com>, "Jan Kara" <firstname.lastname@example.org>, "Bjorn Helgaas" <email@example.com>, "Linux PCI" <firstname.lastname@example.org> Subject: Re: [PATCH v5 11/15] PCI: Obey iomem restrictions for procfs mmap Date: Wed, 4 Nov 2020 10:50:17 -0600 [thread overview] Message-ID: <20201104165017.GA352206@bjorn-Precision-5520> (raw) In-Reply-To: <CAKMK7uF0QjesaNs97N-G8cZkXuAmFgcmTfHvoCP94br_WVcV6Q@mail.gmail.com> On Wed, Nov 04, 2020 at 09:44:04AM +0100, Daniel Vetter wrote: > On Tue, Nov 3, 2020 at 11:09 PM Dan Williams <email@example.com> wrote: > > On Tue, Nov 3, 2020 at 1:28 PM Bjorn Helgaas <firstname.lastname@example.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 <email@example.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. > > Still has some value since it enforces exclusive access even if the > config isn't enabled, and iirc e1000 had some fun with userspace tools > clobbering the firmware and bricking the chip. There's *some* value; I'm just skeptical since only three drivers use it. IORESOURCE_EXCLUSIVE is from e8de1481fd71 ("resource: allow MMIO exclusivity for device drivers"), and the commit message says this is only active when CONFIG_STRICT_DEVMEM is set. I didn't check to see whether that's still true. That commit adds a bunch of wrappers and "__"-prefixed functions to pass the IORESOURCE_EXCLUSIVE flag around. That's a fair bit of uglification for three drivers. > Another thing I kinda wondered, since pci maintainer is here: At least > in drivers/gpu I see very few drivers explicitly requestion regions > (this might be a historical artifact due to the shadow attach stuff > before we had real modesetting drivers). And pci core doesn't do that > either, even when a driver is bound. Is this intentional, or > should/could we do better? Since drivers work happily without > reserving regions I don't think "the drivers need to remember to do > this" will ever really work out well. You're right, many drivers don't call pci_request_regions(). Maybe we could do better, but I haven't looked into that recently. There is a related note in Documentation/PCI/pci.rst that's been there for a long time (it refers to "pci_request_resources()", which has never existed AFAICT). I'm certainly open to proposals.
next prev parent reply other threads:[~2020-11-04 16:51 UTC|newest] Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top [not found] <firstname.lastname@example.org> 2020-10-30 10:08 ` Daniel Vetter 2020-11-03 21:28 ` Bjorn Helgaas 2020-11-03 22:09 ` Dan Williams 2020-11-04 8:44 ` Daniel Vetter 2020-11-04 16:50 ` Bjorn Helgaas [this message] 2020-11-04 20:12 ` Dan Williams 2020-11-05 9:34 ` Daniel Vetter 2020-10-30 10:08 ` [PATCH v5 14/15] sysfs: Support zapping of binary attr mmaps Daniel Vetter 2020-10-30 10:08 ` [PATCH v5 15/15] PCI: Revoke mappings like devmem Daniel Vetter 2020-10-30 19:22 ` Dan Williams 2020-11-03 21:30 ` Bjorn Helgaas
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