Re: [PATCH v5 8/9] xen/gntdev.c: Convert to use vm_insert_range

[Boris Ostrovsky]

On 1/2/19 1:58 PM, Souptick Joarder wrote:
> On Mon, Dec 24, 2018 at 6:53 PM Souptick Joarder <jrdr.linux@xxxxxxxxx> wrote:
>> Convert to use vm_insert_range() to map range of kernel
>> memory to user vma.
>>
>> Signed-off-by: Souptick Joarder <jrdr.linux@xxxxxxxxx>
>> Reviewed-by: Matthew Wilcox <willy@xxxxxxxxxxxxx>
>> Reviewed-by: Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>
>> ---
>>  drivers/xen/gntdev.c | 11 ++++-------
>>  1 file changed, 4 insertions(+), 7 deletions(-)
>>
>> diff --git a/drivers/xen/gntdev.c b/drivers/xen/gntdev.c
>> index b0b02a5..430d4cb 100644
>> --- a/drivers/xen/gntdev.c
>> +++ b/drivers/xen/gntdev.c
>> @@ -1084,7 +1084,7 @@ static int gntdev_mmap(struct file *flip, struct vm_area_struct *vma)
>>         int index = vma->vm_pgoff;
>>         int count = vma_pages(vma);
>>         struct gntdev_grant_map *map;
>> -       int i, err = -EINVAL;
>> +       int err = -EINVAL;
>>
>>         if ((vma->vm_flags & VM_WRITE) && !(vma->vm_flags & VM_SHARED))
>>                 return -EINVAL;
>> @@ -1145,12 +1145,9 @@ static int gntdev_mmap(struct file *flip, struct vm_area_struct *vma)
>>                 goto out_put_map;
>>
>>         if (!use_ptemod) {
>> -               for (i = 0; i < count; i++) {
>> -                       err = vm_insert_page(vma, vma->vm_start + i*PAGE_SIZE,
>> -                               map->pages[i]);
>> -                       if (err)
>> -                               goto out_put_map;
>> -               }
> Looking into the original code, the loop should run from i =0 to *i <
> map->count*.
> There is no error check for *count > map->count* and we might end up
> overrun the map->pages[i] boundary.

I don't think we can have map->count != count (see
gntdev_find_map_index()). But for clarity I agree using map->count might
be better.


>
> While converting this code with suggested vm_insert_range(), this can be fixed.

And count can be dropped altogether.


Thanks.
-boris


>
>
>> +               err = vm_insert_range(vma, vma->vm_start, map->pages, count);
>> +               if (err)
>> +                       goto out_put_map;
>>         } else {
>>  #ifdef CONFIG_X86
>>                 /*
>> --
>> 1.9.1
>>