Re: [PATCH 1/2] sigaltstack: implement SS_AUTODISARM flag

[Stas Sergeev]

29.02.2016 00:13, Stas Sergeev пишет:

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 <mi...@redhat.com>
CC: Peter Zijlstra <pet...@infradead.org>
CC: Richard Weinberger <rich...@nod.at>
CC: Andrew Morton <a...@linux-foundation.org>
CC: Oleg Nesterov <o...@redhat.com>
CC: Tejun Heo <t...@kernel.org>
CC: Heinrich Schuchardt <xypron.g...@gmx.de>
CC: Jason Low <jason.l...@hp.com>
CC: Andrea Arcangeli <aarca...@redhat.com>
CC: Frederic Weisbecker <fweis...@gmail.com>
CC: Konstantin Khlebnikov <khlebni...@yandex-team.ru>
CC: Josh Triplett <j...@joshtriplett.org>
CC: "Eric W. Biederman" <ebied...@xmission.com>
CC: Aleksa Sarai <cyp...@cyphar.com>
CC: "Amanieu d'Antras" <aman...@gmail.com>
CC: Paul Moore <pmo...@redhat.com>
CC: Sasha Levin <sasha.le...@oracle.com>
CC: Palmer Dabbelt <pal...@dabbelt.com>
CC: Vladimir Davydov <vdavy...@parallels.com>
CC: linux-kernel@vger.kernel.org
CC: linux-...@vger.kernel.org
CC: Andy Lutomirski <l...@amacapital.net>

Signed-off-by: Stas Sergeev <s...@users.sourceforge.net>
---
  include/linux/sched.h       |  1 +
  include/linux/signal.h      |  4 +++-
  include/uapi/linux/signal.h |  3 +++
  kernel/fork.c               |  4 +++-
  kernel/signal.c             | 23 ++++++++++++-----------
  5 files changed, 22 insertions(+), 13 deletions(-)

diff --git a/include/linux/sched.h b/include/linux/sched.h
index a10494a..f561d34 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; diff --git a/include/linux/signal.h b/include/linux/signal.h

index 92557bb..be3ebe0 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) \
+               t->sas_ss_size = 0; \

Should also reset flags here...
Will send v4.