UIO: Fix mapping of logical and virtual memory

mmap() doesn't work as expected for UIO_MEM_LOGICAL or UIO_MEM_VIRTUAL
mappings. The offset into the memory needs to be added, otherwise
uio_vma_fault always returns the first page only. Note that for UIO
userspace calls mmap() with offset = N * getpagesize() to access
mapping N. This must be compensated when calculating the offset. A
comment was added to explain this since it is not obvious.

Signed-off-by: Andrew G. Harvey <agh@cisco.com>
Signed-off-by: Hans J. Koch <hjk@linutronix.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

1 files changed, 10 insertions, 2 deletions

diff --git a/drivers/uio/uio.c b/drivers/uio/uio.c
index 557e73ef5884..5dccf057a7dd 100644
--- a/drivers/uio/uio.c
+++ b/drivers/uio/uio.c
@@ -490,15 +490,23 @@ static int uio_vma_fault(struct vm_area_struct *vma, struct vm_fault *vmf)
 {
         struct uio_device *idev = vma->vm_private_data;
         struct page *page;
+        unsigned long offset;
 
         int mi = uio_find_mem_index(vma);
         if (mi < 0)
                 return VM_FAULT_SIGBUS;
 
+        /*
+         * We need to subtract mi because userspace uses offset = N*PAGE_SIZE
+         * to use mem[N].
+         */
+        offset = (vmf->pgoff - mi) << PAGE_SHIFT;
+
         if (idev->info->mem[mi].memtype == UIO_MEM_LOGICAL)
-                page = virt_to_page(idev->info->mem[mi].addr);
+                page = virt_to_page(idev->info->mem[mi].addr + offset);
         else
-                page = vmalloc_to_page((void*)idev->info->mem[mi].addr);
+                page = vmalloc_to_page((void *)idev->info->mem[mi].addr
+                                                        + offset);
         get_page(page);
         vmf->page = page;
         return 0;