Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751451AbcCFUKu (ORCPT ); Sun, 6 Mar 2016 15:10:50 -0500 Received: from mail-ob0-f178.google.com ([209.85.214.178]:33191 "EHLO mail-ob0-f178.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750890AbcCFUKl (ORCPT ); Sun, 6 Mar 2016 15:10:41 -0500 MIME-Version: 1.0 In-Reply-To: References: <1456781345-8243-1-git-send-email-stsp@list.ru> <1456781345-8243-2-git-send-email-stsp@list.ru> From: Andy Lutomirski Date: Sun, 6 Mar 2016 12:10:21 -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 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 4073 Lines: 108 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. --Andy