lists.openwall.net | lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening PHC | |
Open Source and information security mailing list archives
| ||
|
Date: Sat, 14 May 2016 14:18:14 +0300 From: Stas Sergeev <stsp@...t.ru> To: Andy Lutomirski <luto@...capital.net> Cc: Thomas Gleixner <tglx@...utronix.de>, Pavel Emelyanov <xemul@...allels.com>, Shuah Khan <shuahkh@....samsung.com>, X86 ML <x86@...nel.org>, Andrew Morton <akpm@...ux-foundation.org>, Linux API <linux-api@...r.kernel.org>, Jason Low <jason.low2@...com>, "Eric W. Biederman" <ebiederm@...ssion.com>, Aleksa Sarai <cyphar@...har.com>, Josh Triplett <josh@...htriplett.org>, "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, Paul Moore <pmoore@...hat.com>, Sasha Levin <sasha.levin@...cle.com>, Denys Vlasenko <dvlasenk@...hat.com>, Al Viro <viro@...iv.linux.org.uk>, Borislav Petkov <bp@...en8.de>, Amanieu d'Antras <amanieu@...il.com>, Konstantin Khlebnikov <khlebnikov@...dex-team.ru>, Heinrich Schuchardt <xypron.glpk@....de>, Brian Gerst <brgerst@...il.com>, Tejun Heo <tj@...nel.org>, Linus Torvalds <torvalds@...ux-foundation.org>, Andrea Arcangeli <aarcange@...hat.com>, Frederic Weisbecker <fweisbec@...il.com>, Palmer Dabbelt <palmer@...belt.com>, Vladimir Davydov <vdavydov@...allels.com>, Oleg Nesterov <oleg@...hat.com>, Richard Weinberger <richard@....at>, "H. Peter Anvin" <hpa@...or.com>, Peter Zijlstra <peterz@...radead.org> Subject: Re: [PATCH 1/4] signals/sigaltstack: If SS_AUTODISARM, bypass on_sig_stack 14.05.2016 07:18, Andy Lutomirski пишет: > On May 8, 2016 7:05 PM, "Stas Sergeev" <stsp@...t.ru> wrote: >> 09.05.2016 04:32, Andy Lutomirski пишет: >> >>> On May 7, 2016 7:38 AM, "Stas Sergeev" <stsp@...t.ru> wrote: >>>> 03.05.2016 20:31, Andy Lutomirski пишет: >>>> >>>>> If a signal stack is set up with SS_AUTODISARM, then the kernel >>>>> inherently avoids incorrectly resetting the signal stack if signals >>>>> recurse: the signal stack will be reset on the first signal >>>>> delivery. This means that we don't need check the stack pointer >>>>> when delivering signals if SS_AUTODISARM is set. >>>>> >>>>> This will make segmented x86 programs more robust: currently there's >>>>> a hole that could be triggered if ESP/RSP appears to point to the >>>>> signal stack but actually doesn't due to a nonzero SS base. >>>>> >>>>> Signed-off-by: Stas Sergeev <stsp@...t.ru> >>>>> Cc: Al Viro <viro@...iv.linux.org.uk> >>>>> Cc: Aleksa Sarai <cyphar@...har.com> >>>>> Cc: Amanieu d'Antras <amanieu@...il.com> >>>>> Cc: Andrea Arcangeli <aarcange@...hat.com> >>>>> Cc: Andrew Morton <akpm@...ux-foundation.org> >>>>> Cc: Andy Lutomirski <luto@...capital.net> >>>>> Cc: Borislav Petkov <bp@...en8.de> >>>>> Cc: Brian Gerst <brgerst@...il.com> >>>>> Cc: Denys Vlasenko <dvlasenk@...hat.com> >>>>> Cc: Eric W. Biederman <ebiederm@...ssion.com> >>>>> Cc: Frederic Weisbecker <fweisbec@...il.com> >>>>> Cc: H. Peter Anvin <hpa@...or.com> >>>>> Cc: Heinrich Schuchardt <xypron.glpk@....de> >>>>> Cc: Jason Low <jason.low2@...com> >>>>> Cc: Josh Triplett <josh@...htriplett.org> >>>>> Cc: Konstantin Khlebnikov <khlebnikov@...dex-team.ru> >>>>> Cc: Linus Torvalds <torvalds@...ux-foundation.org> >>>>> Cc: Oleg Nesterov <oleg@...hat.com> >>>>> Cc: Palmer Dabbelt <palmer@...belt.com> >>>>> Cc: Paul Moore <pmoore@...hat.com> >>>>> Cc: Pavel Emelyanov <xemul@...allels.com> >>>>> Cc: Peter Zijlstra <peterz@...radead.org> >>>>> Cc: Richard Weinberger <richard@....at> >>>>> Cc: Sasha Levin <sasha.levin@...cle.com> >>>>> Cc: Shuah Khan <shuahkh@....samsung.com> >>>>> Cc: Tejun Heo <tj@...nel.org> >>>>> Cc: Thomas Gleixner <tglx@...utronix.de> >>>>> Cc: Vladimir Davydov <vdavydov@...allels.com> >>>>> Cc: linux-api@...r.kernel.org >>>>> Cc: linux-kernel@...r.kernel.org >>>>> Signed-off-by: Andy Lutomirski <luto@...nel.org> >>>>> --- >>>>> include/linux/sched.h | 12 ++++++++++++ >>>>> 1 file changed, 12 insertions(+) >>>>> >>>>> diff --git a/include/linux/sched.h b/include/linux/sched.h >>>>> index 2950c5cd3005..8f03a93348b9 100644 >>>>> --- a/include/linux/sched.h >>>>> +++ b/include/linux/sched.h >>>>> @@ -2576,6 +2576,18 @@ static inline int kill_cad_pid(int sig, int priv) >>>>> */ >>>>> static inline int on_sig_stack(unsigned long sp) >>>>> { >>>>> + /* >>>>> + * If the signal stack is AUTODISARM then, by construction, we >>>>> + * can't be on the signal stack unless user code deliberately set >>>>> + * SS_AUTODISARM when we were already on the it. >>>> "on the it" -> "on it". >>>> >>>> Anyway, I am a bit puzzled with this patch. >>>> You say "unless user code deliberately set >>>> >>>> SS_AUTODISARM when we were already on the it" >>>> so what happens in case it actually does? >>>> >>> Stack corruption. Don't do that. >> Only after your change, I have to admit. :) >> >> >>>> Without your patch: if user sets up the same sas - no stack switch. >>>> if user sets up different sas - stack switch on nested signal. >>>> >>>> With your patch: stack switch in any case, so if user >>>> set up same sas - stack corruption by nested signal. >>>> >>>> Or am I missing the intention? >>> The intention is to make everything completely explicit. With >>> SS_AUTODISARM, the kernel knows directly whether you're on the signal >>> stack, and there should be no need to look at sp. If you set >>> SS_AUTODISARM and get a signal, the signal stack gets disarmed. If >>> you take a nested signal, it's delivered normally. When you return >>> all the way out, the signal stack is re-armed. >>> >>> For DOSEMU, this means that no 16-bit register state can possibly >>> cause a signal to be delivered wrong, because the register state when >>> a signal is raised won't affect delivery, which seems like a good >>> thing to me. >> Yes, but doesn't affect dosemu1 which doesn't use SS_AUTODISARM. >> So IMHO the SS check should still be added, even if not for dosemu2. >> >> >>> If this behavior would be problematic for you, can you explain why? >> Only theoretically: if someone sets SS_AUTODISARM inside a >> sighandler. Since this doesn't give EPERM, I wouldn't deliberately >> make it a broken scenario (esp if it wasn't before the particular change). >> Ideally it would give EPERM, but we can't, so doesn't matter much. >> I just wanted to warn about the possible regression. > I suppose we could return an error if you are on the sigstack when > setting SS_AUTODISARM, although I was hoping to avoid yet more special > cases. Hmm. How about extending the generic check then? Currently it is roughly: if (on_sig_stack(sp)) return -EPERM; and we could do: if (on_sig_stack(sp) || on_new_sas(new_sas, sp)) return -EPERM; Looks like it will close the potential hole opened by your commit without introducing the special case for SS_AUTODISARM. What do you think?
Powered by blists - more mailing lists