From: Andy Lutomirski <luto@amacapital.net>
To: Stas Sergeev <stsp@list.ru>
Cc: Ingo Molnar <mingo@kernel.org>, X86 ML <x86@kernel.org>,
Linux kernel <linux-kernel@vger.kernel.org>,
Linus Torvalds <torvalds@linux-foundation.org>,
"H. Peter Anvin" <hpa@zytor.com>,
Thomas Gleixner <tglx@linutronix.de>,
Brian Gerst <brgerst@gmail.com>, Borislav Petkov <bp@alien8.de>,
Stas Sergeev <stsp@users.sourceforge.net>
Subject: Re: [regression] x86/signal/64: Fix SS handling for signals delivered to 64-bit programs breaks dosemu
Date: Thu, 13 Aug 2015 09:42:49 -0700 [thread overview]
Message-ID: <CALCETrVg43=e05BW7S7BXOC3ei4gd1RbJcsiHti_V5ttbhPZTQ@mail.gmail.com> (raw)
In-Reply-To: <55CCC812.5010101@list.ru>
On Thu, Aug 13, 2015 at 9:38 AM, Stas Sergeev <stsp@list.ru> wrote:
> 13.08.2015 19:24, Andy Lutomirski пишет:
>
>> On Thu, Aug 13, 2015 at 9:20 AM, Stas Sergeev <stsp@list.ru> wrote:
>>>
>>> 13.08.2015 19:09, Andy Lutomirski пишет:
>>>
>>>> On Thu, Aug 13, 2015 at 9:03 AM, Stas Sergeev <stsp@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.
>
> Isn't uc_flags read-only for the user?
> I look into setup_rt_frame
> <http://lxr.free-electrons.com/ident?v=2.4.37;i=setup_rt_frame>() and see
> ---
> /* Create the ucontext. */
> err |= __put_user(0, &frame->uc.uc_flags);
> ---
> so it doesn't look like the flag that user can use to _request_
> something from the kernel. And I am talking about exactly
> the flag to request the new behaviour, as only that can remove
> the regression completely without patching dosemu.
User code could rewrite it in the signal handler to request something.
--Andy
next prev parent reply other threads:[~2015-08-13 16:43 UTC|newest]
Thread overview: 121+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-08-12 0:17 [regression] x86/signal/64: Fix SS handling for signals delivered to 64-bit programs breaks dosemu Stas Sergeev
2015-08-12 0:38 ` Andy Lutomirski
2015-08-12 8:02 ` Stas Sergeev
2015-08-12 16:19 ` Andy Lutomirski
2015-08-12 17:00 ` Stas Sergeev
2015-08-12 18:25 ` Andy Lutomirski
2015-08-12 18:55 ` Stas Sergeev
2015-08-12 19:20 ` Andy Lutomirski
2015-08-12 19:55 ` Stas Sergeev
2015-08-12 20:01 ` Andy Lutomirski
2015-08-12 20:14 ` Stas Sergeev
2015-08-12 20:28 ` Andy Lutomirski
2015-08-12 20:45 ` Stas Sergeev
2015-08-12 20:47 ` Andy Lutomirski
2015-08-12 20:55 ` Stas Sergeev
2015-08-12 21:37 ` Andy Lutomirski
2015-08-12 21:50 ` Stas Sergeev
2015-08-12 22:00 ` Andy Lutomirski
2015-08-13 8:39 ` Ingo Molnar
2015-08-13 10:14 ` Stas Sergeev
2015-08-13 12:44 ` Stas Sergeev
2015-08-13 14:58 ` Andy Lutomirski
2015-08-13 15:22 ` Stas Sergeev
2015-08-13 15:38 ` Andy Lutomirski
2015-08-13 16:03 ` Stas Sergeev
2015-08-13 16:09 ` Andy Lutomirski
2015-08-13 16:20 ` Stas Sergeev
2015-08-13 16:24 ` Andy Lutomirski
2015-08-13 16:38 ` Stas Sergeev
2015-08-13 16:42 ` Andy Lutomirski [this message]
2015-08-13 16:48 ` Stas Sergeev
2015-08-13 16:59 ` Andy Lutomirski
2015-08-13 17:13 ` Stas Sergeev
2015-08-13 17:17 ` Andy Lutomirski
2015-08-13 18:00 ` Stas Sergeev
2015-08-13 18:05 ` Andy Lutomirski
2015-08-13 18:19 ` Stas Sergeev
2015-08-13 18:25 ` Andy Lutomirski
2015-08-13 18:35 ` Stas Sergeev
2015-08-22 12:38 ` Ingo Molnar
2015-08-22 14:19 ` Stas Sergeev
2015-08-23 6:25 ` Ingo Molnar
2015-08-13 11:08 ` Stas Sergeev
2015-08-13 15:37 ` Linus Torvalds
2015-08-13 15:43 ` Andy Lutomirski
2015-08-13 16:19 ` Linus Torvalds
2015-08-13 16:23 ` Andy Lutomirski
2015-08-13 16:34 ` Linus Torvalds
2015-08-13 16:43 ` Linus Torvalds
2015-08-13 16:44 ` Andy Lutomirski
2015-08-13 17:00 ` Brian Gerst
2015-08-18 6:29 ` Stas Sergeev
2015-08-18 22:42 ` Andy Lutomirski
2015-08-18 22:47 ` Andy Lutomirski
2015-08-19 9:35 ` Stas Sergeev
2015-08-19 15:46 ` Andy Lutomirski
2015-08-19 16:30 ` Stas Sergeev
2015-09-02 5:12 ` Andy Lutomirski
2015-09-02 9:17 ` Stas Sergeev
2015-09-02 14:21 ` Andy Lutomirski
2015-09-02 15:02 ` Andy Lutomirski
2015-09-02 17:46 ` Stas Sergeev
2015-09-02 18:17 ` Andy Lutomirski
2015-09-02 18:23 ` Stas Sergeev
2015-09-02 19:06 ` Andy Lutomirski
2015-09-02 21:01 ` Stas Sergeev
2015-09-02 21:39 ` Andy Lutomirski
2015-09-02 22:25 ` Stas Sergeev
2015-09-02 22:25 ` Andy Lutomirski
2015-09-02 23:01 ` Stas Sergeev
2015-08-19 10:10 ` Stas Sergeev
2015-08-19 15:35 ` Andy Lutomirski
2015-08-14 8:10 ` Cyrill Gorcunov
2015-08-13 17:51 ` Stas Sergeev
2015-08-13 18:35 ` Linus Torvalds
2015-08-13 18:41 ` Andy Lutomirski
2015-08-13 19:05 ` Stas Sergeev
2015-08-13 19:49 ` Andy Lutomirski
2015-08-13 20:09 ` Stas Sergeev
2015-08-13 19:53 ` Linus Torvalds
2015-08-13 20:08 ` Cyrill Gorcunov
2015-08-13 20:09 ` Linus Torvalds
2015-08-13 21:42 ` Raymond Jennings
2015-08-13 21:46 ` Linus Torvalds
2015-08-13 22:01 ` Raymond Jennings
2015-08-13 22:05 ` Stas Sergeev
2015-08-13 23:05 ` Linus Torvalds
2015-08-13 23:18 ` Linus Torvalds
2015-08-13 23:35 ` Raymond Jennings
2015-08-13 23:43 ` Stas Sergeev
2015-08-14 0:02 ` Linus Torvalds
2015-08-13 22:02 ` Stas Sergeev
2015-08-13 22:11 ` Andy Lutomirski
2015-08-13 22:25 ` Stas Sergeev
2015-08-13 22:29 ` Andy Lutomirski
2015-08-13 22:51 ` Stas Sergeev
2015-08-13 23:00 ` Andy Lutomirski
2015-08-13 23:17 ` Stas Sergeev
2015-08-14 0:00 ` Stas Sergeev
2015-08-14 0:05 ` Andy Lutomirski
2015-08-14 0:17 ` Stas Sergeev
2015-08-14 0:27 ` Linus Torvalds
2015-08-14 0:50 ` Stas Sergeev
2015-08-14 1:21 ` Andy Lutomirski
2015-08-14 1:32 ` Stas Sergeev
2015-08-14 1:37 ` Andy Lutomirski
2015-08-14 2:03 ` Stas Sergeev
2015-08-18 6:19 ` Stas Sergeev
2015-08-14 0:08 ` Linus Torvalds
2015-08-14 0:24 ` Andy Lutomirski
2015-08-14 0:40 ` Linus Torvalds
2015-08-14 7:22 ` Cyrill Gorcunov
2015-08-14 10:02 ` Pavel Emelyanov
2015-08-14 10:53 ` Cyrill Gorcunov
2015-08-13 18:57 ` Stas Sergeev
2015-08-13 19:01 ` Andy Lutomirski
2015-08-13 19:13 ` Stas Sergeev
2015-08-13 19:37 ` Linus Torvalds
2015-08-13 19:59 ` Stas Sergeev
2015-08-13 20:07 ` Linus Torvalds
2015-08-18 6:40 ` Stas Sergeev
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