linux-kernel - Re: [PATCH] fs, elf: Make sure to page align bss in load_elf

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Date:   Fri, 6 Jul 2018 09:13:23 +0200
From:   Oscar Salvador <osalvador@...hadventures.net>
To:     Kees Cook <keescook@...omium.org>
Cc:     "linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
        Linux-MM <linux-mm@...ck.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Michal Hocko <mhocko@...e.com>,
        Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>,
        Nicolas Pitre <nicolas.pitre@...aro.org>,
        Oscar Salvador <osalvador@...e.de>,
        Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH] fs, elf: Make sure to page align bss in load_elf_library

On Thu, Jul 05, 2018 at 08:44:18AM -0700, Kees Cook wrote:
> On Thu, Jul 5, 2018 at 7:55 AM,  <osalvador@...hadventures.net> wrote:
> > From: Oscar Salvador <osalvador@...e.de>
> >
> > The current code does not make sure to page align bss before calling
> > vm_brk(), and this can lead to a VM_BUG_ON() in __mm_populate()
> > due to the requested lenght not being correctly aligned.
> >
> > Let us make sure to align it properly.
> >
> > Signed-off-by: Oscar Salvador <osalvador@...e.de>
> > Tested-by: Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>
> > Reported-by: syzbot+5dcb560fe12aa5091c06@...kaller.appspotmail.com
> 
> Wow. CONFIG_USELIB? I'm surprised distros are still using this. 32-bit
> only, and libc5 and earlier only.
> 
> Regardless, this appears to match the current bss alignment logic in
> the main elf loader, so:
> 
> Acked-by: Kees Cook <keescook@...omium.org>
> 
> -Kees
> 
> > ---
> >  fs/binfmt_elf.c | 5 ++---
> >  1 file changed, 2 insertions(+), 3 deletions(-)
> >
> > diff --git a/fs/binfmt_elf.c b/fs/binfmt_elf.c
> > index 0ac456b52bdd..816cc921cf36 100644
> > --- a/fs/binfmt_elf.c
> > +++ b/fs/binfmt_elf.c
> > @@ -1259,9 +1259,8 @@ static int load_elf_library(struct file *file)
> >                 goto out_free_ph;
> >         }
> >
> > -       len = ELF_PAGESTART(eppnt->p_filesz + eppnt->p_vaddr +
> > -                           ELF_MIN_ALIGN - 1);
> > -       bss = eppnt->p_memsz + eppnt->p_vaddr;
> > +       len = ELF_PAGEALIGN(eppnt->p_filesz + eppnt->p_vaddr);
> > +       bss = ELF_PAGEALIGN(eppnt->p_memsz + eppnt->p_vaddr);
> >         if (bss > len) {
> >                 error = vm_brk(len, bss - len);
> >                 if (error)
> > --
> > 2.13.6
> >
CC Andrew

Hi Andrew,

in case this patch gets accepted, does it have to go through your tree?
Or is it for someone else to take it?

Thanks
-- 
Oscar Salvador
SUSE L3