On Mon, Feb 29, 2016 at 1:29 PM, Stas Sergeev <s...@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 <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 | 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?
> 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;
This is poorly named. How about "ss_mode = ss_flags & SS_MODE_MASK";
--Andy
