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

[Bjorn Helgaas]

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.

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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