Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751582AbcCFURs (ORCPT ); Sun, 6 Mar 2016 15:17:48 -0500 Received: from smtp14.mail.ru ([94.100.181.95]:60957 "EHLO smtp14.mail.ru" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750960AbcCFURi (ORCPT ); Sun, 6 Mar 2016 15:17:38 -0500 Subject: Re: [PATCH 1/2] sigaltstack: implement SS_AUTODISARM flag To: Andy Lutomirski References: <1456781345-8243-1-git-send-email-stsp@list.ru> <1456781345-8243-2-git-send-email-stsp@list.ru> 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 From: Stas Sergeev Message-ID: <56DC904C.2060708@list.ru> Date: Sun, 6 Mar 2016 23:17:16 +0300 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.6.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 8bit X-Mras: Ok Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 4371 Lines: 108 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?