Re: Are vDSO addresses special?

* Andy Lutomirski:

quoted

On Feb 11, 2021, at 2:05 AM, Florian Weimer [off-list ref] 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
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