linux-kernel - Re: [RFC PATCH v1 1/1] binfmt

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <CABi2SkU_TW1+NE6ofFSwiS+XV89d8T-NZy7X+OQi-2dG06O25w@mail.gmail.com>
Date: Mon, 5 Aug 2024 14:33:57 -0700
From: Jeff Xu <jeffxu@...omium.org>
To: Kees Cook <kees@...nel.org>
Cc: akpm@...ux-foundation.org, jannh@...gle.com, sroettger@...gle.com, 
	adhemerval.zanella@...aro.org, ojeda@...nel.org, adobriyan@...il.com, 
	linux-kernel@...r.kernel.org, linux-mm@...ck.org, jorgelo@...omium.org
Subject: Re: [RFC PATCH v1 1/1] binfmt_elf: mseal address zero

On Mon, Aug 5, 2024 at 2:05 PM Kees Cook <kees@...nel.org> wrote:
>
> On Thu, Aug 01, 2024 at 05:08:33PM +0000, jeffxu@...omium.org wrote:
> > From: Jeff Xu <jeffxu@...omium.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@...omium.org>
> > ---
> >  fs/binfmt_elf.c    | 4 ++++
> >  include/linux/mm.h | 4 ++++
> >  mm/mseal.c         | 2 +-
> >  3 files changed, 9 insertions(+), 1 deletion(-)
> >
> > diff --git a/fs/binfmt_elf.c b/fs/binfmt_elf.c
> > index 19fa49cd9907..e4d35d6f5d65 100644
> > --- a/fs/binfmt_elf.c
> > +++ b/fs/binfmt_elf.c
> > @@ -1314,6 +1314,10 @@ 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);
> > +
> > +#ifdef CONFIG_64BIT
> > +             do_mseal(0, PAGE_SIZE, 0);
> > +#endif
>
> Instead of wrapping this in #ifdefs, does it make more sense to adjust
> the mm.h declaration instead, like this below...
>
Sure.

> >       }
> >
> >       regs = current_pt_regs();
> > diff --git a/include/linux/mm.h b/include/linux/mm.h
> > index c4b238a20b76..b5fed60ddcd9 100644
> > --- a/include/linux/mm.h
> > +++ b/include/linux/mm.h
> > @@ -4201,4 +4201,8 @@ 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
> > +int do_mseal(unsigned long start, size_t len_in, unsigned long flags);
>
> #else
> static inline int do_mseal(unsigned long start, size_t len_in, unsigned long flags)
> {
>         return -ENOTSUPP;
> }
>
OK.

> > +#endif
> > +
> >  #endif /* _LINUX_MM_H */
> > diff --git a/mm/mseal.c b/mm/mseal.c
> > index bf783bba8ed0..7a40a84569c8 100644
> > --- a/mm/mseal.c
> > +++ b/mm/mseal.c
> > @@ -248,7 +248,7 @@ static int apply_mm_seal(unsigned long start, unsigned long end)
> >   *
> >   *  unseal() is not supported.
> >   */
> > -static int do_mseal(unsigned long start, size_t len_in, unsigned long flags)
> > +int do_mseal(unsigned long start, size_t len_in, unsigned long flags)
> >  {
> >       size_t len;
> >       int ret = 0;
> > --
> > 2.46.0.rc1.232.g9752f9e123-goog
> >
>
> And if it returns an error code, should we check it when used in
> load_elf_binary()? (And if so, should the mm.h return 0 for non-64bit?)
>
It shouldn't fail. I can add pr_warning to handle the error case:
pr_warning("pid=%d, couldn't seal the page on address 0.\n",
task_pid_nr(current));

Thanks!
Best regards,
-Jeff


> --
> Kees Cook