Re: [PATCHv3 3/6] x86/arch_prctl/vdso: add ARCH_MAP_VDSO_*

[Dmitry Safonov]

On 08/31/2016 06:00 PM, Andy Lutomirski wrote:
> On Fri, Aug 26, 2016 at 10:13 AM, Dmitry Safonov <dsafonov@xxxxxxxxxxxxx> wrote:
> > Add API to change vdso blob type with arch_prctl.
> > As this is usefull only by needs of CRIU, expose
> > this interface under CONFIG_CHECKPOINT_RESTORE.
> >
> > Cc: Andy Lutomirski <luto@xxxxxxxxxx>
> > Cc: Oleg Nesterov <oleg@xxxxxxxxxx>
> > Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
> > Cc: "H. Peter Anvin" <hpa@xxxxxxxxx>
> > Cc: Ingo Molnar <mingo@xxxxxxxxxx>
> > Cc: linux-mm@xxxxxxxxx
> > Cc: x86@xxxxxxxxxx
> > Cc: Cyrill Gorcunov <gorcunov@xxxxxxxxxx>
> > Cc: Pavel Emelyanov <xemul@xxxxxxxxxxxxx>
> > Signed-off-by: Dmitry Safonov <dsafonov@xxxxxxxxxxxxx>
> > ---
> >  arch/x86/entry/vdso/vma.c         | 45 ++++++++++++++++++++++++++++++---------
> >  arch/x86/include/asm/vdso.h       |  2 ++
> >  arch/x86/include/uapi/asm/prctl.h |  6 ++++++
> >  arch/x86/kernel/process_64.c      | 25 ++++++++++++++++++++++
> >  4 files changed, 68 insertions(+), 10 deletions(-)
> >
> > diff --git a/arch/x86/entry/vdso/vma.c b/arch/x86/entry/vdso/vma.c
> > index 5bcb25a9e573..dad2b2d8ff03 100644
> > --- a/arch/x86/entry/vdso/vma.c
> > +++ b/arch/x86/entry/vdso/vma.c
> > @@ -176,6 +176,16 @@ static int vvar_fault(const struct vm_special_mapping *sm,
> >         return VM_FAULT_SIGBUS;
> >  }
> >
> > +static const struct vm_special_mapping vdso_mapping = {
> > +       .name = "[vdso]",
> > +       .fault = vdso_fault,
> > +       .mremap = vdso_mremap,
> > +};
> > +static const struct vm_special_mapping vvar_mapping = {
> > +       .name = "[vvar]",
> > +       .fault = vvar_fault,
> > +};
> > +
> >  /*
> >   * Add vdso and vvar mappings to current process.
> >   * @image          - blob to map
> > @@ -188,16 +198,6 @@ static int map_vdso(const struct vdso_image *image, unsigned long addr)
> >         unsigned long text_start;
> >         int ret = 0;
> >
> > -       static const struct vm_special_mapping vdso_mapping = {
> > -               .name = "[vdso]",
> > -               .fault = vdso_fault,
> > -               .mremap = vdso_mremap,
> > -       };
> > -       static const struct vm_special_mapping vvar_mapping = {
> > -               .name = "[vvar]",
> > -               .fault = vvar_fault,
> > -       };
> > -
> >         if (down_write_killable(&mm->mmap_sem))
> >                 return -EINTR;
> >
> > @@ -256,6 +256,31 @@ static int map_vdso_randomized(const struct vdso_image *image)
> >         return map_vdso(image, addr);
> >  }
> >
> > +int map_vdso_once(const struct vdso_image *image, unsigned long addr)
> > +{
> > +       struct mm_struct *mm = current->mm;
> > +       struct vm_area_struct *vma;
> > +
> > +       down_write(&mm->mmap_sem);
> > +       /*
> > +        * Check if we have already mapped vdso blob - fail to prevent
> > +        * abusing from userspace install_speciall_mapping, which may
> > +        * not do accounting and rlimit right.
> > +        * We could search vma near context.vdso, but it's a slowpath,
> > +        * so let's explicitely check all VMAs to be completely sure.
> > +        */
> > +       for (vma = mm->mmap; vma; vma = vma->vm_next) {
> > +               if (vma->vm_private_data == &vdso_mapping ||
> > +                               vma->vm_private_data == &vvar_mapping) {
>
> Should probably also check that vm_ops == &special_mapping_vmops,
> which means that maybe there should be a:
>
> static inline bool vma_is_special_mapping(const struct vm_area_struct
> *vma, const struct vm_special_mapping &sm);

Well, yep, I thought about it, but left without it to not touch
additional headers.
Will do for the next version, thanks!