Messages in this thread | | | Subject | Re: [PATCH 1/2] sigaltstack: implement SS_AUTODISARM flag | From | Stas Sergeev <> | Date | Sun, 6 Mar 2016 23:17:16 +0300 |
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06.03.2016 23:10, Andy Lutomirski пишет: > On Sun, Mar 6, 2016 at 12:07 PM, Andy Lutomirski <luto@amacapital.net> wrote: >> On Mon, Feb 29, 2016 at 1:29 PM, Stas Sergeev <stsp@list.ru> 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 <mingo@redhat.com> >>> CC: Peter Zijlstra <peterz@infradead.org> >>> CC: Richard Weinberger <richard@nod.at> >>> CC: Andrew Morton <akpm@linux-foundation.org> >>> CC: Oleg Nesterov <oleg@redhat.com> >>> CC: Tejun Heo <tj@kernel.org> >>> CC: Heinrich Schuchardt <xypron.glpk@gmx.de> >>> CC: Jason Low <jason.low2@hp.com> >>> CC: Andrea Arcangeli <aarcange@redhat.com> >>> CC: Frederic Weisbecker <fweisbec@gmail.com> >>> CC: Konstantin Khlebnikov <khlebnikov@yandex-team.ru> >>> CC: Josh Triplett <josh@joshtriplett.org> >>> CC: "Eric W. Biederman" <ebiederm@xmission.com> >>> CC: Aleksa Sarai <cyphar@cyphar.com> >>> CC: "Amanieu d'Antras" <amanieu@gmail.com> >>> CC: Paul Moore <pmoore@redhat.com> >>> CC: Sasha Levin <sasha.levin@oracle.com> >>> CC: Palmer Dabbelt <palmer@dabbelt.com> >>> CC: Vladimir Davydov <vdavydov@parallels.com> >>> CC: linux-kernel@vger.kernel.org >>> CC: linux-api@vger.kernel.org >>> CC: Andy Lutomirski <luto@amacapital.net> >>> >>> Signed-off-by: Stas Sergeev <stsp@users.sourceforge.net> >>> --- >>> 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?
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