Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751405AbcCFUzs (ORCPT ); Sun, 6 Mar 2016 15:55:48 -0500 Received: from mail-oi0-f44.google.com ([209.85.218.44]:35275 "EHLO mail-oi0-f44.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750928AbcCFUzk convert rfc822-to-8bit (ORCPT ); Sun, 6 Mar 2016 15:55:40 -0500 MIME-Version: 1.0 In-Reply-To: <56DC904C.2060708@list.ru> References: <1456781345-8243-1-git-send-email-stsp@list.ru> <1456781345-8243-2-git-send-email-stsp@list.ru> <56DC904C.2060708@list.ru> From: Andy Lutomirski Date: Sun, 6 Mar 2016 12:55:19 -0800 Message-ID: Subject: Re: [PATCH 1/2] sigaltstack: implement SS_AUTODISARM flag To: Stas Sergeev Cc: Ingo Molnar , Peter Zijlstra , Richard Weinberger , Andrew Morton , Oleg Nesterov , Tejun Heo , Heinrich Schuchardt , Jason Low , Andrea Arcangeli , Frederic Weisbecker , Konstantin Khlebnikov , Josh Triplett , "Eric W. Biederman" , Aleksa Sarai , "Amanieu d'Antras" , Paul Moore , Sasha Levin , Palmer Dabbelt , Vladimir Davydov , "linux-kernel@vger.kernel.org" , Linux API , Stas Sergeev Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8BIT Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 4785 Lines: 129 On Sun, Mar 6, 2016 at 12:17 PM, Stas Sergeev wrote: > 06.03.2016 23:10, Andy Lutomirski пишет: > >> On Sun, Mar 6, 2016 at 12:07 PM, Andy Lutomirski >> wrote: >>> >>> On Mon, Feb 29, 2016 at 1:29 PM, Stas Sergeev wrote: >>>> >>>> This patch implements the SS_AUTODISARM flag that can be ORed with >>>> SS_ONSTACK when forming ss_flags. >>>> When this flag is set, sigaltstack will be disabled when entering >>>> the signal handler; more precisely, after saving sas to uc_stack. >>>> When leaving the signal handler, the sigaltstack is restored by >>>> uc_stack. >>>> When this flag is used, it is safe to switch from sighandler with >>>> swapcontext(). Without this flag, the subsequent signal will corrupt >>>> the state of the switched-away sighandler. >>>> >>>> CC: Ingo Molnar >>>> CC: Peter Zijlstra >>>> CC: Richard Weinberger >>>> CC: Andrew Morton >>>> CC: Oleg Nesterov >>>> CC: Tejun Heo >>>> CC: Heinrich Schuchardt >>>> CC: Jason Low >>>> CC: Andrea Arcangeli >>>> CC: Frederic Weisbecker >>>> CC: Konstantin Khlebnikov >>>> CC: Josh Triplett >>>> CC: "Eric W. Biederman" >>>> CC: Aleksa Sarai >>>> CC: "Amanieu d'Antras" >>>> CC: Paul Moore >>>> CC: Sasha Levin >>>> CC: Palmer Dabbelt >>>> CC: Vladimir Davydov >>>> CC: linux-kernel@vger.kernel.org >>>> CC: linux-api@vger.kernel.org >>>> CC: Andy Lutomirski >>>> >>>> Signed-off-by: Stas Sergeev >>>> --- >>>> include/linux/sched.h | 8 ++++++++ >>>> include/linux/signal.h | 4 +++- >>>> include/uapi/linux/signal.h | 3 +++ >>>> kernel/fork.c | 2 +- >>>> kernel/signal.c | 23 ++++++++++++----------- >>>> 5 files changed, 27 insertions(+), 13 deletions(-) >>>> >>>> diff --git a/include/linux/sched.h b/include/linux/sched.h >>>> index a10494a..26201cd 100644 >>>> --- a/include/linux/sched.h >>>> +++ b/include/linux/sched.h >>>> @@ -1587,6 +1587,7 @@ struct task_struct { >>>> >>>> unsigned long sas_ss_sp; >>>> size_t sas_ss_size; >>>> + unsigned sas_ss_flags; >>>> >>>> struct callback_head *task_works; >>>> >>>> @@ -2573,6 +2574,13 @@ static inline int sas_ss_flags(unsigned long sp) >>>> return on_sig_stack(sp) ? SS_ONSTACK : 0; >>>> } >>>> >>>> +static inline void sas_ss_reset(struct task_struct *p) >>>> +{ >>>> + p->sas_ss_sp = 0; >>>> + p->sas_ss_size = 0; >>>> + p->sas_ss_flags = SS_DISABLE; >>>> +} >>>> + >>>> static inline unsigned long sigsp(unsigned long sp, struct ksignal >>>> *ksig) >>>> { >>>> if (unlikely((ksig->ka.sa.sa_flags & SA_ONSTACK)) && ! >>>> sas_ss_flags(sp)) >>>> diff --git a/include/linux/signal.h b/include/linux/signal.h >>>> index 92557bb..3fbe814 100644 >>>> --- a/include/linux/signal.h >>>> +++ b/include/linux/signal.h >>>> @@ -432,8 +432,10 @@ int __save_altstack(stack_t __user *, unsigned >>>> long); >>>> stack_t __user *__uss = uss; \ >>>> struct task_struct *t = current; \ >>>> put_user_ex((void __user *)t->sas_ss_sp, &__uss->ss_sp); \ >>>> - put_user_ex(sas_ss_flags(sp), &__uss->ss_flags); \ >>>> + put_user_ex(t->sas_ss_flags, &__uss->ss_flags); \ >>>> put_user_ex(t->sas_ss_size, &__uss->ss_size); \ >>>> + if (t->sas_ss_flags & SS_AUTODISARM) \ >>>> + sas_ss_reset(t); \ >>>> } while (0); >>>> >>>> #ifdef CONFIG_PROC_FS >>>> diff --git a/include/uapi/linux/signal.h b/include/uapi/linux/signal.h >>>> index e1bd50c2..4691bc5 100644 >>>> --- a/include/uapi/linux/signal.h >>>> +++ b/include/uapi/linux/signal.h >>>> @@ -6,5 +6,8 @@ >>>> >>>> #define SS_ONSTACK 1 >>>> #define SS_DISABLE 2 >>>> +#define SS_VALMASK 0xf >>> >>> SS_MODE_MASK, perhaps? >> >> Actually, let's invert that. >> >> #define SS_AUTODISARM (1U << 31) >> #define SS_FLAG_BITS SS_AUTODISARM >> >> ss_mode = ss_flags & ~SS_FLAG_BITS; >> >> this way flag bits that are currently undefined will continue to trigger >> EINVAL. > > OK, will do. > Though I am still going to keep SS_AUTODISARM =(1 << 4) - > it doesn't matter from what side we add new flags, does it? Adding them starting with a high bit means that more low bits are available for use as mode numbers. Admittedly, this barely matters. --Andy -- Andy Lutomirski AMA Capital Management, LLC