linux-kernel - Re: [PATCH v5 8/9] xen/gntdev.c: Convert to use vm_insert

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Date:   Thu, 3 Jan 2019 00:28:19 +0530
From:   Souptick Joarder <jrdr.linux@...il.com>
To:     Andrew Morton <akpm@...ux-foundation.org>,
        Matthew Wilcox <willy@...radead.org>,
        Michal Hocko <mhocko@...e.com>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        Juergen Gross <jgross@...e.com>,
        Russell King - ARM Linux <linux@...linux.org.uk>,
        robin.murphy@....com
Cc:     xen-devel@...ts.xenproject.org, linux-kernel@...r.kernel.org,
        Linux-MM <linux-mm@...ck.org>
Subject: Re: [PATCH v5 8/9] xen/gntdev.c: Convert to use vm_insert_range

On Mon, Dec 24, 2018 at 6:53 PM Souptick Joarder <jrdr.linux@...il.com> wrote:
>
> Convert to use vm_insert_range() to map range of kernel
> memory to user vma.
>
> Signed-off-by: Souptick Joarder <jrdr.linux@...il.com>
> Reviewed-by: Matthew Wilcox <willy@...radead.org>
> Reviewed-by: Boris Ostrovsky <boris.ostrovsky@...cle.com>
> ---
>  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.

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


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