Re: [PATCH v2] ld.so: Handle read-only dynamic section gracefully [BZ #28340]

[Florian Weimer via Libc-alpha <libc-alpha@sourceware.org>]

* Siddhesh Poyarekar:

> On 9/15/21 4:10 PM, Florian Weimer wrote:
>> As far as I can tell, this does not check whether the DYNAMIC segment is
>> actually covered by a read-write LOAD segment.  I wonder how much value
>> this imperfect check has.
>
> I reckon there's less value in trying to make this corner case work; I
> can't think of a reason for someone (outside of the VDSO use case) to
> do this on purpose.  Read-only DYNAMIC segments in ET_DYN objects
> shouldn't be a supported use case.

Sure, but the corresponding LOAD segment is read-only as well, that's
what actually matters.

>> Would it make more sense to fix the kernel linker script that generates
>> those bogus vDSO reference files?
>
> The vdso is not meant to be relocated, which is why all segments in it
> are read-only.  setup_vdso only pretends to relocate it in the
> interest of internal consistency in ld.so.

And they do not want multiple LOAD segments because it can fit all on
the same page.  We would end up with an RWX segment if we made this
single LOAD segment writable, which is probably even more confusing.

So I guess the status quo is probably best.

Maybe someone else can comment on the additional detection.  In the
past, we said that crashes on corrupt ELF files weren't something we
cared about, but I increasingly see th value of good diagnostics for
common special cases.

(See also the discussion about DSOs without entry points.)

Thanks,
Florian