Re: [PATCH v7 6/7] mseal, system mappings: uprobe mapping

[Jeff Xu <jeffxu@chromium.org>]

On Mon, Feb 24, 2025 at 10:24 PM Lorenzo Stoakes
<lorenzo.stoakes@oracle.com> wrote:
>
> On Mon, Feb 24, 2025 at 10:52:45PM +0000, jeffxu@chromium.org wrote:
> > From: Jeff Xu <jeffxu@chromium.org>
> >
> > Provide support to mseal the uprobe mapping.
> >
> > Unlike other system mappings, the uprobe mapping is not
> > established during program startup. However, its lifetime is the same
> > as the process's lifetime. It could be sealed from creation.
> >
>
> I thought we agreed not to enable this for now? What testing
> have you done to ensure this is functional?
>
I honestly don't know much about uprobe. I don't recall that I agree
to ignore that though.

As indicated in the cover letter, it is my understanding that uprobe's
mapping's lifetime are the same as process's lifetime, thus sealable.
[1]
Oleg Nesterov, also cc, seems OK with mseal it in the early version of
this patch [2]

Are there any potential downsides of doing this? If yes, I can remove it.

I'm also looking at Oleg to give more guidance on this :-), or if
there are some functional tests that I need to do for uprobe.


[1] https://lore.kernel.org/all/20241005200741.GA24353@redhat.com/
[2] https://lore.kernel.org/all/20241005200741.GA24353@redhat.com/

> I mean is this literally _all_ uprobe mappings now being sealed?
>
> I'd really like some more assurances on this one. And what are you
> mitigating by sealing these? I get VDSO (kinda) but uprobes?
>
> You really need to provide more justification here.

Sure. In our threat model, we need to seal all r-x, r--, and --x
mappings to prevent them from becoming writable. This applies to all
mappings, regardless of whether they're created by the kernel or
dynamic linker.


> > Signed-off-by: Jeff Xu <jeffxu@chromium.org>
> > ---
> >  kernel/events/uprobes.c | 5 ++++-
> >  1 file changed, 4 insertions(+), 1 deletion(-)
> >
> > diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c
> > index 2ca797cbe465..8dcdfa0d306b 100644
> > --- a/kernel/events/uprobes.c
> > +++ b/kernel/events/uprobes.c
> > @@ -1662,6 +1662,7 @@ static const struct vm_special_mapping xol_mapping = {
> >  static int xol_add_vma(struct mm_struct *mm, struct xol_area *area)
> >  {
> >       struct vm_area_struct *vma;
> > +     unsigned long vm_flags;
> >       int ret;
> >
> >       if (mmap_write_lock_killable(mm))
> > @@ -1682,8 +1683,10 @@ static int xol_add_vma(struct mm_struct *mm, struct xol_area *area)
> >               }
> >       }
> >
> > +     vm_flags = VM_EXEC|VM_MAYEXEC|VM_DONTCOPY|VM_IO;
> > +     vm_flags |= VM_SEALED_SYSMAP;
> >       vma = _install_special_mapping(mm, area->vaddr, PAGE_SIZE,
> > -                             VM_EXEC|VM_MAYEXEC|VM_DONTCOPY|VM_IO,
> > +                             vm_flags,
> >                               &xol_mapping);
> >       if (IS_ERR(vma)) {
> >               ret = PTR_ERR(vma);
> > --
> > 2.48.1.658.g4767266eb4-goog
> >