[PATCH] Call _dl_open_check after relocation is finished [BZ #24259]

[Florian Weimer]

* H. J. Lu:

>> If you report the error at this, doesn't this mean the object is still
>> around and in a bad state?  This looks related to this bug:
>
> Yes.
>
>>   <https://sourceware.org/bugzilla/show_bug.cgi?id=20839>
>>
>> Would the CET bug go away if we got rid after the object without trace
>> after a failure in _dl_open_check?
>
> Yes.
>
>> I can look into fixing the other bug, but I don't know how hard that's
>> going to be.

I did that now and the required infrastructure changes are fairly
involved.  So I think we should add something that works today.

A natural place for the CET compatibility check would be
elf_machine_reject_phdr_p (currently used only on MIPS).  This way, we
can continue searching for a CET-compatible library along the search
path.

>> > diff --git a/sysdeps/x86/tst-cet-legacy-5.c b/sysdeps/x86/tst-cet-legacy-5.c
>> > new file mode 100644
>> > index 0000000000..fbf640f664
>> > --- /dev/null
>> > +++ b/sysdeps/x86/tst-cet-legacy-5.c
>>
>> > +static void
>> > +do_test_1 (const char *modname, bool fail)
>> > +{
>> > +  int (*fp) (void);
>> > +  void *h;
>> > +
>> > +  h = dlopen (modname, RTLD_LAZY);
>> > +  if (h == NULL)
>> > +    {
>> > +      if (fail)
>> > +     {
>> > +       const char *err = dlerror ();
>> > +       if (strstr (err, "shadow stack isn't enabled") == NULL)
>> > +         {
>> > +           printf ("incorrect dlopen '%s' error: %s\n", modname,
>> > +                   dlerror ());
>> > +           exit (1);
>> > +         }
>> > +
>> > +       return;
>> > +     }
>>
>> Is the return supposed to be taken if running on non-CET hardware?  I'm
>> looking for the UNSUPPORTED case.
>
> This path is taken only on CET hardware.  For non-CET hardware, 'h' shouldn't
> be NULL.

Please add logging to the test for the unsupported case, so that the aim
of the test is clearer and when it fails to achieve its objective.

Thanks,
Florian