From: Dan Williams <firstname.lastname@example.org> To: Bjorn Helgaas <email@example.com> Cc: "Daniel Vetter" <firstname.lastname@example.org>, "DRI Development" <email@example.com>, LKML <firstname.lastname@example.org>, "KVM list" <email@example.com>, "Linux MM" <firstname.lastname@example.org>, "Linux ARM" <email@example.com>, linux-samsung-soc <firstname.lastname@example.org>, "Linuxemail@example.com" <firstname.lastname@example.org>, "Daniel Vetter" <email@example.com>, "Jason Gunthorpe" <firstname.lastname@example.org>, "Kees Cook" <email@example.com>, "Andrew Morton" <firstname.lastname@example.org>, "John Hubbard" <email@example.com>, "Jérôme Glisse" <firstname.lastname@example.org>, "Jan Kara" <email@example.com>, "Bjorn Helgaas" <firstname.lastname@example.org>, "Linux PCI" <email@example.com> Subject: Re: [PATCH v5 11/15] PCI: Obey iomem restrictions for procfs mmap Date: Wed, 4 Nov 2020 12:12:15 -0800 [thread overview] Message-ID: <CAPcyv4idORJzHVD2vCOnO3REqWHKVn_-otOzTBf0HhcWq4iJRQ@mail.gmail.com> (raw) In-Reply-To: <20201104165017.GA352206@bjorn-Precision-5520> On Wed, Nov 4, 2020 at 8:50 AM Bjorn Helgaas <firstname.lastname@example.org> wrote: > > 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. It seems a bug that the kernel permits MMIO regions with side effects to be ioremap()'ed without request_mem_region() on the resource. I wonder how much log spam would happen if ioremap() reported whenever a non-IORESOURE_BUSY range was passed to it? The current state of affairs to trust *remap users to have claimed their remap target seems too ingrained to unwind now.
next prev parent reply other threads:[~2020-11-04 20:12 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 2020-11-04 20:12 ` Dan Williams [this message] 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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