Re: [PATCH 2/4] elf: Move note processing after l_phdr is updated [BZ #26831]

H.J. Lu
2020-11-03T12:37:40Z

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.