[PATCHv3 12/27] x86/vdso: Restrict splitting VVAR VMA

[Jann Horn]

On Thu, Apr 25, 2019 at 6:17 PM Dmitry Safonov <dima at arista.com> wrote:
> Although, time namespace can work with VVAR VMA split, it seems worth
> to forbid splitting VVAR resulting in stricter ABI and reducing amount
> of corner-cases to consider while working further on VDSO.
[...]
> diff --git a/arch/x86/entry/vdso/vma.c b/arch/x86/entry/vdso/vma.c
> index babc4e7a519c..ff9875a4d53b 100644
> --- a/arch/x86/entry/vdso/vma.c
> +++ b/arch/x86/entry/vdso/vma.c
[...]
> +static int vvar_mremap(const struct vm_special_mapping *sm,
> +               struct vm_area_struct *new_vma)
> +{
> +       unsigned long new_size = new_vma->vm_end - new_vma->vm_start;
> +       const struct vdso_image *image = current->mm->context.vdso_image;

Using current->mm in here is a bit awkward. So far the ->mremap
handler can only be invoked for `current`, but still, maybe
new_vma->vm_mm would be better here?

> +       if (new_size != -image->sym_vvar_start)
> +               return -EINVAL;
> +
> +       return 0;
> +}
[...]