Re: Are vDSO addresses special?

[Florian Weimer <fweimer@redhat.com>]

* Andy Lutomirski:

>> On Feb 11, 2021, at 2:05 AM, Florian Weimer <fweimer@redhat.com> wrote:
>> 
>> In glibc, we have some code that copies the DT_SONAME string of the
>> kernel vDSO into the heap, commented this way:
>> 
>>             /* Work around a kernel problem.  The kernel cannot handle
>>                addresses in the vsyscall DSO pages in writev() calls.  */
>> 
>> Is this really a problem anymore?  vDSO addresses are ordinary userspace
>> addresses, I think.  (The vsyscall stuff is very different, of course,
>> and maybe the vDSO started out the same way.)
>
> I don’t think it was ever a problem, and it certainly haven’t been a
> problem for a long, long time. vDSO addresses are regular user
> addresses.  The *vsyscall* addresses are not, and most syscalls will
> not accept them, but that shouldn’t matter especially since modern
> kernels, by default, won’t let you read those addresses from user code
> either.

Thanks.  Patch posted:

<https://sourceware.org/pipermail/libc-alpha/2021-February/122603.html>

> Saying “vsyscall DSO” is odd. There’s no such thing.

In the glibc context, it sometimes means “system-call-like function
implemented in the vDSO”.  But that's not the case here.

Florian
-- 
Red Hat GmbH, https://de.redhat.com/ , Registered seat: Grasbrunn,
Commercial register: Amtsgericht Muenchen, HRB 153243,
Managing Directors: Charles Cachera, Brian Klemm, Laurie Krebs, Michael O'Neill