Re: [PATCH] Check multiple NT_GNU_PROPERTY_TYPE_0 notes [BZ #23509]

[Florian Weimer <fweimer at redhat dot com>]

On 08/15/2018 05:29 PM, H.J. Lu wrote:
> On Wed, Aug 15, 2018 at 8:25 AM, Florian Weimer <fweimer@redhat.com> wrote:
> > On 08/15/2018 05:23 PM, H.J. Lu wrote:
> > > On Wed, Aug 15, 2018 at 8:17 AM, Florian Weimer <fweimer@redhat.com>
> > > wrote:
> > > > On 08/14/2018 08:12 PM, H.J. Lu wrote:
> > > > > _dl_process_cet_property_note is called on on each PT_NOTE segment.
> > > > > We must keep searching until we found a PT_NOTE segment with a
> > > > > NT_GNU_PROPERTY_TYPE_0 note:
> > > > >
> > > > >      /* Skip if we have seen a NT_GNU_PROPERTY_TYPE_0 note before.  */
> > > > >      if (l->l_cet != lc_unknown)
> > > > >        return;
> > > > > ...
> > > >
> > > >
> > > >
> > > > What if there are different segments, each one with its own
> > > > NT_GNU_PROPERTY_TYPE_0?  Wouldn't that point to lack of linker support,
> > > > too?
> > > > So that CET needs to be disabled?
> > >
> > >
> > > Older linkers puts all NT_GNU_PROPERTY_TYPE_0 notes in one
> > > .note.gnu.property section.  One can certainly create some random notes
> > > which look like NT_GNU_PROPERTY_TYPE_0.  I don't think we need to
> > > check these notes.
> >
> >
> > I think older BFD ld creates multiple segments.
>
> Which version of ld dos that?

Examples that got me worried look like this:

$ readelf -l /usr/bin/b5i2iso
…
  NOTE           0x0000000000000334 0x0000000000400334 0x0000000000400334
                 0x0000000000000020 0x0000000000000020  R      0x4
  NOTE           0x0000000000000358 0x0000000000400358 0x0000000000400358
                 0x0000000000000030 0x0000000000000030  R      0x8
  NOTE           0x0000000000000388 0x0000000000400388 0x0000000000400388
                 0x0000000000000024 0x0000000000000024  R      0x4
…
   07     .note.ABI-tag
   08     .note.gnu.property
   09     .note.gnu.build-id
…
$ rpm -qf /usr/bin/b5i2iso
AcetoneISO-6.7-26.fc29.x86_64

Per 
<https://kojipkgs.fedoraproject.org//packages/AcetoneISO/6.7/26.fc29/data/logs/x86_64/root.log>, 
this was built with binutils-2.30.90-4.fc29.

I don't know enough about the binutils linker to be certain that 
allocatable SHT_NOTE sections of the same name always go into the same 
PT_NOTE segment.  In the example above, the sections weren't split.

Thanks,
Florian