Re: [RFC PATCH v3 1/2] drivers: pci: fix pci_mmap_fits() implementation for procfs mmap

[Bjorn Helgaas]

On Wed, Jan 21, 2015 at 06:44:56PM +0000, Lorenzo Pieralisi wrote:
> Hi Bjorn,
> 
> On Fri, Nov 21, 2014 at 05:51:14PM +0000, Bjorn Helgaas wrote:
> > On Thu, Nov 13, 2014 at 11:19:15AM +0000, Lorenzo Pieralisi wrote:
> > > The introduction of pci_mmap_fits() in commit:
> > > 
> > > b5ff7df3df9efab511244d5a299fce706c71af48
> > > "Check mapped ranges on sysfs resource files"
> > > 
> > > allowed to check for valid range mappings of PCI resources to user space
> > > when mapping PCI resources through the sysfs filesystem.
> > > 
> > > The mapping of resources through the sysfs expects the offset passed
> > > by the user through the mmap syscall to be 0, and the pgoff is adjusted
> > > by the kernel to memory map the resource to the CPU physical address
> > > corresponding to the PCI resource in question.
> > > 
> > > The usage of procfs mapping of PCI resources (/proc/bus/pci files)
> > > is more controversial in that userspace programs mapping PCI resources
> > > are expected to pass in the mmap offset field either a CPU physical address
> > > or a PCI bar value, depending on the architecture.
> > > 
> > > By the time pci_mmap_fits() was used to check PCI resource ranges for
> > > procfs PCI resources mapping in commit:
> > > 
> > > 9eff02e2042f96fb2aedd02e032eca1c5333d7
> > > "PCI: check mmap range of /proc/bus/pci files too"
> > > 
> > > the procfs interface for mmapping resources to user space broke, since
> > > pci_mmap_fits() expected the offset passed from user space in the mmap
> > > call to be 0, not the CPU physical address or PCI BAR value of the
> > > resource in question.
> > > 
> > > Subsequent attempts at fixing the pci_mmap_fits() implementation failed
> > > to fix the issue (or fixed the issue in some architectures but not for
> > > all of them, ARM and SPARC procfs interface PCI resources mapping stayed
> > > broken throughout) in particular commits:
> > > 
> > > 8c05cd08a7504b855c265263e84af61aabafa329
> > > "PCI: fix offset check for sysfs mmapped files"
> > > 
> > > and
> > > 
> > > 3b519e4ea618b6943a82931630872907f9ac2c2b
> > > "PCI: fix size checks for mmap() on /proc/bus/pci files"
> > > 
> > > fixed procfs PCI resources mapping checks in pci_mmap_fits for some
> > > architectures, but not for architectures like SPARC that expects
> > > the offset value passed from user space through the mmap syscall
> > > (when mapping through procfs) to represent the PCI BAR value of the
> > > resource to be mapped.
> > > 
> > > The reason behind the breakage is the following. The addresses stored
> > > in PCI device resources for memory spaces correspond to CPU physical
> > > addresses, which do not necessarily map 1:1 to PCI bus addresses as
> > > programmed in PCI devices configuration spaces.
> > > 
> > > This implies that the sanity checks carried out in pci_mmap_fits() to
> > > ensure that the user executes an mmap of a "real" pci resource are
> > > erroneous when executed through procfs. Some platforms (ie SPARC)
> > > expect the offset value to be passed in (procfs mapping) to be the
> > > PCI BAR configuration value as read from the PCI device configuration
> > > space, not the fixed-up CPU physical address that is present in PCI
> > > device resources.
> > > 
> > > The required pgoff (offset in mmap syscall) value passed from userspace
> > > is supposed to represent the resource value exported through
> > > /proc/bus/pci/devices when the resource is mmapped though procfs (and 0
> > > when the mapping is carried out through sysfs resource files), which
> > > corresponds to the PCI resource filtered through the pci_resource_to_user()
> > > API.
> > > 
> > > This patch converts the PCI resource to the expected "user visible"
> > > value through pci_resource_to_user() before carrying out sanity checks
> > > in pci_mmap_fits() so that the check is carried out on the resource
> > > values as expected from the userspace mmap API.
> > > 
> > > Cc: Arnd Bergmann <arnd@xxxxxxxx>
> > > Cc: Jesse Barnes <jbarnes@xxxxxxxxxxxxxxxx>
> > > Cc: Bjorn Helgaas <bhelgaas@xxxxxxxxxx>
> > > Cc: Benjamin Herrenschmidt <benh@xxxxxxxxxxxxxxxxxxx>
> > > Cc: Russell King <linux@xxxxxxxxxxxxxxxx>
> > > Cc: David S. Miller <davem@xxxxxxxxxxxxx>
> > > Cc: Michal Simek <monstr@xxxxxxxxx>
> > > Cc: Martin Wilck <martin.wilck@xxxxxxxxxxxxxx>
> > > Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@xxxxxxx>
> > 
> > Hi Lorenzo,
> > 
> > I think this patch is the right thing to do.  I'm going to try to write
> > patches for microblaze, mips, powerpc, and sparc that implement their
> > pci_resource_to_user() in terms of pcibios_resource_to_bus() (the patches
> > are easy; it's the arguments for correctness that take time).  Then I'll
> > try to convince myself that those arches are currently broken and will be
> > fixed by your patch below.
> > 
> > But I'll be on vacation all next week, so this will take me some time and
> > it may not make the next merge window.
> 
> I do not know if you had time to implement the patches above, I would
> like to ask Russell to merge patch 2 of this series though, since (1) it
> is a fix in the first place given the current proc/sys interface, and
> (2) we need it to remove dependency on pcibios for arm64 drivers; I am
> just waiting to merge patch 2 upstream since in a way it depends on your
> decision on what the final proc/sys interface should look like and how
> we implement it.
> 
> As things stand, patch 2 can be merged and fixes the current API on ARM.

I haven't had a chance to do anything with these, sorry.  The second patch
only touches ARM, and I think it's fine to merge that.  I'll ack it in case
that's useful to you.

Bjorn

> > > ---
> > >  drivers/pci/pci-sysfs.c | 13 ++++++++-----
> > >  1 file changed, 8 insertions(+), 5 deletions(-)
> > > 
> > > diff --git a/drivers/pci/pci-sysfs.c b/drivers/pci/pci-sysfs.c
> > > index 2c6643f..e4634e3 100644
> > > --- a/drivers/pci/pci-sysfs.c
> > > +++ b/drivers/pci/pci-sysfs.c
> > > @@ -963,17 +963,20 @@ void pci_remove_legacy_files(struct pci_bus *b)
> > >  int pci_mmap_fits(struct pci_dev *pdev, int resno, struct vm_area_struct *vma,
> > >  		  enum pci_mmap_api mmap_api)
> > >  {
> > > -	unsigned long nr, start, size, pci_start;
> > > +	unsigned long nr, start, size, pci_offset;
> > > +	resource_size_t pci_start, pci_end;
> > >  
> > >  	if (pci_resource_len(pdev, resno) == 0)
> > >  		return 0;
> > >  	nr = vma_pages(vma);
> > >  	start = vma->vm_pgoff;
> > > +	pci_resource_to_user(pdev, resno, &pdev->resource[resno],
> > > +			     &pci_start, &pci_end);
> > >  	size = ((pci_resource_len(pdev, resno) - 1) >> PAGE_SHIFT) + 1;
> > > -	pci_start = (mmap_api == PCI_MMAP_PROCFS) ?
> > > -			pci_resource_start(pdev, resno) >> PAGE_SHIFT : 0;
> > > -	if (start >= pci_start && start < pci_start + size &&
> > > -			start + nr <= pci_start + size)
> > > +	pci_offset = (mmap_api == PCI_MMAP_PROCFS) ?
> > > +			pci_start >> PAGE_SHIFT : 0;
> > > +	if (start >= pci_offset && start < pci_offset + size &&
> > > +			start + nr <= pci_offset + size)
> > >  		return 1;
> > >  	return 0;
> > >  }
> > > -- 
> > > 2.1.2
> > > 
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