[PATCH v14 04/17] PCI: Check resource alignment for /sys pci_mmap_resource path

[Yinghai Lu]

When user access /sys/.../resourceX  with pci_mmap_resource(),
pci_mmap_resource():
  ...
  pci_resource_to_user(pdev, i, res, &start, &end);
  vma->vm_pgoff += start >> PAGE_SHIFT;
  mmap_type = res->flags & IORESOURCE_MEM ? pci_mmap_mem : pci_mmap_io;
  return pci_mmap_page_range(pdev, vma, mmap_type, write_combine);
so it will return virtual address for round_down of start.

user code should pass offset with PAGE_SIZE offset.
  fd = open(argv[1], O_RDONLY);
  ...
  sscanf(argv[2], "0x%lx", &offset);
  left = offset & (PAGE_SIZE - 1);
  offset &= PAGE_MASK;
  addr = mmap(NULL, PAGE_SIZE, PROT_READ, MAP_SHARED, fd, offset);
  for (i = 0; i < 8; i++)
    printf("%x ", addr[i + left]);
  munmap(addr, PAGE_SIZE);
  close(fd);

When the resource start is not PAGE_SIZE aligned, it should
be io port, pci_mmap_resource could return round_down address of
resource start.
As the whole point for pci_mmap_resource is passing offset in
[0, resource_size), user may assume virtual add is corresponding
to unaligned resource_size. Later they could get wrong value
with offset to resource start.

Block the path for now, and need to use pci_read_resource_io
/pci_write_resource_io path instead.
user code should be like:
  fd = open(argv[1], O_RDONLY);
  ...
  sscanf(argv[2], "0x%lx", &offset);
  for (i = 0; i < 8; i++) {
    pread(fd, &buf, 1, i + offset);
  }
  close(fd);

Signed-off-by: Yinghai Lu <ying...@kernel.org>
---
 drivers/pci/pci-sysfs.c | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/drivers/pci/pci-sysfs.c b/drivers/pci/pci-sysfs.c
index d55d93d..e2eb79f 100644
--- a/drivers/pci/pci-sysfs.c
+++ b/drivers/pci/pci-sysfs.c
@@ -1023,6 +1023,16 @@ static int pci_mmap_resource(struct kobject *kobj, 
struct bin_attribute *attr,
        if (i >= PCI_ROM_RESOURCE)
                return -ENODEV;
 
+       /*
+        * resource start have to be PAGE_SIZE aligned, as we pass
+        * back virt address include round down of resource_start,
+        * that caller can not figure out directly.
+        * when it is not aligned, that mean it is io port, should go
+        * pci_read_resource_io()/pci_write_resource_io() path.
+        */
+       if (res->start & ~PAGE_MASK)
+               return -EINVAL;
+
        if (res->flags & IORESOURCE_MEM && iomem_is_exclusive(res->start))
                return -EINVAL;
 
-- 
2.8.3