Re: [PATCH v2 1/1] binfmt_elf: mseal address zero

[Jeff Xu <jeffxu@chromium.org>]

On Wed, Dec 4, 2024 at 10:04 AM Petr Tesařík <petr@tesarici.cz> wrote:
>
> On Tue,  6 Aug 2024 21:49:27 +0000
> jeffxu@chromium.org wrote:
>
> > From: Jeff Xu <jeffxu@chromium.org>
> >
> > Some legacy SVr4 apps might depend on page on address zero
> > to be readable, however I can't find a reason that the page
> > ever becomes writeable, so seal it.
> >
> > If there is a compain, we can make this configurable.
> >
> > Signed-off-by: Jeff Xu <jeffxu@chromium.org>
> > ---
> >  fs/binfmt_elf.c    |  5 +++++
> >  include/linux/mm.h | 10 ++++++++++
> >  mm/mseal.c         |  2 +-
> >  3 files changed, 16 insertions(+), 1 deletion(-)
> >
> > diff --git a/fs/binfmt_elf.c b/fs/binfmt_elf.c
> > index 19fa49cd9907..f839fa228509 100644
> > --- a/fs/binfmt_elf.c
> > +++ b/fs/binfmt_elf.c
> > @@ -1314,6 +1314,11 @@ static int load_elf_binary(struct linux_binprm *bprm)
> >                  emulate the SVr4 behavior. Sigh. */
> >               error = vm_mmap(NULL, 0, PAGE_SIZE, PROT_READ | PROT_EXEC,
> >                               MAP_FIXED | MAP_PRIVATE, 0);
> > +
> > +             retval = do_mseal(0, PAGE_SIZE, 0);
> > +             if (retval)
> > +                     pr_warn("pid=%d, couldn't seal address 0, ret=%d.\n",
> > +                                     task_pid_nr(current), retval);
> >       }
> >
> >       regs = current_pt_regs();
> > diff --git a/include/linux/mm.h b/include/linux/mm.h
> > index c4b238a20b76..a178c15812eb 100644
> > --- a/include/linux/mm.h
> > +++ b/include/linux/mm.h
> > @@ -4201,4 +4201,14 @@ void vma_pgtable_walk_end(struct vm_area_struct *vma);
> >
> >  int reserve_mem_find_by_name(const char *name, phys_addr_t *start, phys_addr_t *size);
> >
> > +#ifdef CONFIG_64BIT
>
> Strictly speaking, this should be
>
> #if defined(CONFIG_64BIT) && defined(CONFIG_MMU)
>
> But since we do not support any 64-bit architecture without MMU, I'm
> just making this marginal note, so it can be found in ML archives if
> needed.
>
Noted.

Thanks!

> Petr T