On Fri, 26 Oct 2018 at 18:12, Andy Lutomirski <l...@amacapital.net> wrote: > > > > > On Oct 26, 2018, at 2:39 PM, Daniel Micay <danielmi...@gmail.com> wrote: > > > > I ended up working around this with a pthread_atfork handler disabling > > my usage of the feature in the child process for the time being. I > > don't have an easy way to detect if the bug is present within a > > library so > > Can you not just make sure that the fix is backported to all relevant kernels?
There are too many different distribution kernels and I won't be in control of where the software is used. > I suppose we could add a new flag for pkey_get() or something. That would work, since I can apply the workaround (disabling the feature in child processes) if I get EINVAL. The flag wouldn't need to do anything, just existing and being tied to this patch so I have a way to detect that I can safely use MPK after fork. > > I'm going to need a kernel version check with a table of > > kernel releases fixing the problem for each stable branch. > > That won’t work right on district kernels. Please don’t go there. If it's backported to an earlier version, it will just mean missing a chance to use it. I'm not going to assume that it behaves a certain way based on having an old kernel, but rather I just won't use it in a forked child on an older kernel version if I don't have a way to detect the problem. It's for a few different uses in library code so I can't have a runtime test trying to detect it with clone(...). I'd definitely prefer a proper way to detect that I can use it after fork. I really don't want to have a hack like that which is why I'm bringing it up.
