On Thu, Aug 13, 2015 at 9:20 AM, Stas Sergeev <s...@list.ru> wrote: > 13.08.2015 19:09, Andy Lutomirski пишет: > >> On Thu, Aug 13, 2015 at 9:03 AM, Stas Sergeev <s...@list.ru> wrote: >>> >>> 13.08.2015 18:38, Andy Lutomirski пишет: >>>> >>>> >>>> So... what do we do about it? We could revert the whole mess. We >>>> could tell everyone to fix their DOSEMU, which violates policy and is >>>> especially annoying given how much effort we've put into keeping >>>> 16-bit mode fully functional lately. We could add yet more heuristics >>>> and teach sigreturn to ignore the saved SS value in sigcontext if the >>>> saved CS is 64-bit and the saved SS is unusable. >>> >>> Andy, why do you constantly ignore the proposal to make >>> new behaviour explicitly controlable? You don't have to agree >>> with it, but you could at least comment on that possibility >>> and/or mention it with the ones you listed above. >> >> I'm not sure what the proposal is exactly. >> >> We could add a new uc_flags flag. If set, it means that >> sigcontext->ss is valid and should be used by sigreturn. If clear, >> then we ignore sigcontext->ss and just restore __USER_DS. >> >> The problem is that, by itself, this won't fix old DOSEMU. We somehow >> need to either detect that something funny is going on or just leave >> the flag clear by default. >> >> We could do this: always save SS to sigcontext->ss, but only restore >> sigcontext->ss if userspace explicitly sets the flag before sigreturn. >> If we do that, we'd need to also add my patch to preserve the actual >> HW SS selector if possible so that old DOSEMU knows what SS to program >> into its trampoline. >> >> This at least lets *new* DOSEMU set the flag and get the improved >> behavior. I still don't know what effect it'll have on Wine and CRIU. >> >> Stas, is that what you were thinking, or were you thinking of something >> else? > > Not quite. > I mean the flag that will control not only sigreturn, but > the signal delivery as well. This may probably be a sigaction() > flag or some other. If not set - ss is ignored by both signal > delivery and sigreturn(). If set - ss is saved/restored (and in > the future - also fs/gs). > Is such a flag possible?
Maybe. I think I'm more nervous about adding new flags in sigaction than I am in uc_flags. --Andy -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
