Re: [PATCH v2] x86: Remove compat vdso support

Ingo Molnar
2014-03-11T08:37:52Z

* Andy Lutomirski <luto@amacapital.net> wrote:

> [...]
>
> Currently there are three options: sane vDSO, no vDSO, and OpenSuSE
> 9-compatible vDSO. The latter is a mess to maintain and breaks ASLR
> (even for users of modern glibc), and having a vDSO is apparently
> important enough that people are willing to pay to enhance it. The
> default is OpenSuSE 9-compatible vDSO, which is IMO an odd choice.

The 'odd choice' was to not break the ABI by default...

> ISTM the right solution is to make OpenSuSE 9 users turn off the
> vDSO (which is a performance hit for them, but not a correctness
> issue) and let everyone else have a simpler kernel that has no ASLR
> issues.

Could we just remove the option and automagically disable the vdso on
OpenSuSE-9, without any boot flags? Is the segfault distinctive enough
to base a disable-vdso quirk on, either to disable the vdso, or to map
it into the compatibility position on demand?

That would remove most of this complication. Being somewhat slower on
an old distro with a new kernel is perfectly OK. The question is, can
this be done easily enough - chances are that it cannot be done.

Thanks,

Ingo