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


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


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