From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752218AbcB2VaS (ORCPT ); Mon, 29 Feb 2016 16:30:18 -0500 Received: from smtp2.mail.ru ([94.100.179.91]:42366 "EHLO smtp2.mail.ru" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750993AbcB2VaQ (ORCPT ); Mon, 29 Feb 2016 16:30:16 -0500 From: Stas Sergeev To: 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@vger.kernel.org, Andy Lutomirski , Stas Sergeev Subject: [PATCH 1/2] sigaltstack: implement SS_AUTODISARM flag Date: Tue, 1 Mar 2016 00:29:04 +0300 Message-Id: <1456781345-8243-2-git-send-email-stsp@list.ru> X-Mailer: git-send-email 2.7.2 In-Reply-To: <1456781345-8243-1-git-send-email-stsp@list.ru> References: <1456781345-8243-1-git-send-email-stsp@list.ru> X-Mras: Ok Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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 +/* bit-flags */ +#define SS_AUTODISARM (1 << 4) /* disable sas during sighandling */ #endif /* _UAPI_LINUX_SIGNAL_H */ diff --git a/kernel/fork.c b/kernel/fork.c index 2e391c7..68c8716 100644 --- a/kernel/fork.c +++ b/kernel/fork.c @@ -1483,7 +1483,7 @@ static struct task_struct *copy_process(unsigned long clone_flags, * sigaltstack should be cleared when sharing the same VM */ if ((clone_flags & (CLONE_VM|CLONE_VFORK)) == CLONE_VM) - p->sas_ss_sp = p->sas_ss_size = 0; + sas_ss_reset(p); /* * Syscall tracing and stepping should be turned off in the diff --git a/kernel/signal.c b/kernel/signal.c index 0508544..fab6bea 100644 --- a/kernel/signal.c +++ b/kernel/signal.c @@ -3100,13 +3100,14 @@ do_sigaltstack (const stack_t __user *uss, stack_t __user *uoss, unsigned long s if (uss) { void __user *ss_sp; size_t ss_size; - int ss_flags; + unsigned ss_flags; + unsigned ss_xflags; error = -EFAULT; if (!access_ok(VERIFY_READ, uss, sizeof(*uss))) goto out; error = __get_user(ss_sp, &uss->ss_sp) | - __get_user(ss_flags, &uss->ss_flags) | + __get_user(ss_xflags, &uss->ss_flags) | __get_user(ss_size, &uss->ss_size); if (error) goto out; @@ -3115,14 +3116,8 @@ do_sigaltstack (const stack_t __user *uss, stack_t __user *uoss, unsigned long s if (on_sig_stack(sp)) goto out; + ss_flags = ss_xflags & SS_VALMASK; error = -EINVAL; - /* - * Note - this code used to test ss_flags incorrectly: - * old code may have been written using ss_flags==0 - * to mean ss_flags==SS_ONSTACK (as this was the only - * way that worked) - this fix preserves that older - * mechanism. - */ if (ss_flags != SS_DISABLE && ss_flags != SS_ONSTACK && ss_flags != 0) goto out; @@ -3137,6 +3132,7 @@ do_sigaltstack (const stack_t __user *uss, stack_t __user *uoss, unsigned long s current->sas_ss_sp = (unsigned long) ss_sp; current->sas_ss_size = ss_size; + current->sas_ss_flags = ss_xflags; } error = 0; @@ -3167,9 +3163,14 @@ int restore_altstack(const stack_t __user *uss) int __save_altstack(stack_t __user *uss, unsigned long sp) { struct task_struct *t = current; - return __put_user((void __user *)t->sas_ss_sp, &uss->ss_sp) | - __put_user(sas_ss_flags(sp), &uss->ss_flags) | + int err = __put_user((void __user *)t->sas_ss_sp, &uss->ss_sp) | + __put_user(t->sas_ss_flags, &uss->ss_flags) | __put_user(t->sas_ss_size, &uss->ss_size); + if (err) + return err; + if (t->sas_ss_flags & SS_AUTODISARM) + sas_ss_reset(t); + return 0; } #ifdef CONFIG_COMPAT -- 2.7.2