Re: [regression] x86/signal/64: Fix SS handling for signals delivered to 64-bit programs breaks dosemu

[Stas Sergeev]

14.08.2015 04:21, Andy Lutomirski ÐÐÑÐÑ:
> On Thu, Aug 13, 2015 at 5:50 PM, Stas Sergeev <stsp@xxxxxxx> wrote:
> > 14.08.2015 03:27, Linus Torvalds ÐÐÑÐÑ:
> > > On Thu, Aug 13, 2015 at 5:17 PM, Stas Sergeev <stsp@xxxxxxx> wrote:
> > > > For example because you can as well do:
> > > > prctl(ARCH_SET_SIGNAL_SS, 0)
> > > > which will mean "restore ss in sighandler to its current value",
> > > I really think a prctl() is the wrong thing to do.
> > >
> > > If you want a signal handler to save/restore segments, I think it
> > > should be a SA_xyz flag to sigaction() (the way we have SA_RESTART
> > Yes, I was proposing the new sigaction() flag in this thread
> > already too. But at the end, prctl() looks better to me because
> > it allows to pass the TLS value to use when restoring FS.
> > The thing is that I am trying to find the similar treatment for
> > both the SS and FS problems. If you don't think they need a
> > similar treatment, then perhaps the Andy's patch is enough.
> >
> > > etc).  And off by default because of the obvious compatibility issues.
> > Of course.
> >
> > So, what we have right now (in the latest Andy's patch) is:
> > 1. lar heuristics
> > 2. new uc_flags flag
> >
> > What it solves: dosemu's regression.
> >
> > What prctl() can give:
> > - fix to dosemu's regression
> > - fix to the TLS problem in the future
> > - no hack and heuristics
> >
> > With SA_xyz you can only solve the SS problem, so it is
> > probably not any better than the uc_flags things coded
> > up by Andy.
> I'm leaning slightly toward LAR heuristic + SA_SAVE_SS.
Stop right here, doesn't the SA_xyz allow to avoid the
lar heuristic? Why would you still need the lar heuristic then?
Just call it SA_RESTORE_SS instead of SA_SAVE_SS, and
the lar heuristic is gone.

> Unfortunately, I don't think we were clever enough to allow this to be
> probed easily -- we silently ignore unrecognized sa_flags bits.
Big deal, check the kversion. :)

Unforunately, in my eyes SA_xyz doesn't help with FS, so
whether it is better than uc_flags or not, is not what I care
about.
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/