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From:   "H.J. Lu" <hjl.tools@gmail.com>
Date:   Tue, 3 Nov 2020 04:36:42 -0800
Message-ID: <CAMe9rOpmiiBEZqLz-94_MEwgRky+EUsfd=X6Ue30H2c9R=dSKQ@mail.gmail.com>
Subject: Re: [PATCH 2/4] elf: Move note processing after l_phdr is updated [BZ #26831]
To:     Florian Weimer <fweimer@redhat.com>
Cc:     Szabolcs Nagy <szabolcs.nagy@arm.com>,
        GNU C Library <libc-alpha@sourceware.org>,
        Jeremy Linton <jeremy.linton@arm.com>,
        Catalin Marinas <catalin.marinas@arm.com>,
        Mark Rutland <mark.rutland@arm.com>,
        Will Deacon <will.deacon@arm.com>,
        Mark Brown <broonie@kernel.org>,
        Kees Cook <keescook@chromium.org>,
        Salvatore Mesoraca <s.mesoraca16@gmail.com>,
        Lennart Poettering <mzxreary@0pointer.de>,
        Topi Miettinen <toiwoton@gmail.com>,
        LKML <linux-kernel@vger.kernel.org>,
        linux-arm-kernel@lists.infradead.org,
        Kernel Hardening <kernel-hardening@lists.openwall.com>,
        linux-hardening@vger.kernel.org
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On Tue, Nov 3, 2020 at 2:38 AM Florian Weimer <fweimer@redhat.com> wrote:
>
> * Szabolcs Nagy:
>
> > Program headers are processed in two pass: after the first pass
> > load segments are mmapped so in the second pass target specific
> > note processing logic can access the notes.
> >
> > The second pass is moved later so various link_map fields are
> > set up that may be useful for note processing such as l_phdr.
> > ---
> >  elf/dl-load.c | 30 +++++++++++++++---------------
> >  1 file changed, 15 insertions(+), 15 deletions(-)
> >
> > diff --git a/elf/dl-load.c b/elf/dl-load.c
> > index ceaab7f18e..673cf960a0 100644
> > --- a/elf/dl-load.c
> > +++ b/elf/dl-load.c
> > @@ -1259,21 +1259,6 @@ _dl_map_object_from_fd (const char *name, const char *origname, int fd,
> >                                 maplength, has_holes, loader);
> >      if (__glibc_unlikely (errstring != NULL))
> >        goto call_lose;
> > -
> > -    /* Process program headers again after load segments are mapped in
> > -       case processing requires accessing those segments.  Scan program
> > -       headers backward so that PT_NOTE can be skipped if PT_GNU_PROPERTY
> > -       exits.  */
> > -    for (ph = &phdr[l->l_phnum]; ph != phdr; --ph)
> > -      switch (ph[-1].p_type)
> > -     {
> > -     case PT_NOTE:
> > -       _dl_process_pt_note (l, fd, &ph[-1]);
> > -       break;
> > -     case PT_GNU_PROPERTY:
> > -       _dl_process_pt_gnu_property (l, fd, &ph[-1]);
> > -       break;
> > -     }
> >    }
> >
> >    if (l->l_ld == 0)
> > @@ -1481,6 +1466,21 @@ cannot enable executable stack as shared object requires");
> >      /* Assign the next available module ID.  */
> >      l->l_tls_modid = _dl_next_tls_modid ();
> >
> > +  /* Process program headers again after load segments are mapped in
> > +     case processing requires accessing those segments.  Scan program
> > +     headers backward so that PT_NOTE can be skipped if PT_GNU_PROPERTY
> > +     exits.  */
> > +  for (ph = &l->l_phdr[l->l_phnum]; ph != l->l_phdr; --ph)
> > +    switch (ph[-1].p_type)
> > +      {
> > +      case PT_NOTE:
> > +     _dl_process_pt_note (l, fd, &ph[-1]);
> > +     break;
> > +      case PT_GNU_PROPERTY:
> > +     _dl_process_pt_gnu_property (l, fd, &ph[-1]);
> > +     break;
> > +      }
> > +
> >  #ifdef DL_AFTER_LOAD
> >    DL_AFTER_LOAD (l);
> >  #endif
>
> Is this still compatible with the CET requirements?
>
> I hope it is because the CET magic happens in _dl_open_check, so after
> the the code in elf/dl-load.c has run.
>
>

_dl_process_pt_note and _dl_process_pt_gnu_property may call
_dl_signal_error.  Are we prepared to clean more things up when it
happens?  I am investigating:

https://sourceware.org/bugzilla/show_bug.cgi?id=26825

I don't think cleanup of _dl_process_pt_gnu_property failure is done
properly.

-- 
H.J.