On Sun, Mar 6, 2016 at 12:17 PM, Stas Sergeev <[email protected]> wrote: > 06.03.2016 23:10, Andy Lutomirski пишет: > >> On Sun, Mar 6, 2016 at 12:07 PM, Andy Lutomirski <[email protected]> >> wrote: >>> >>> On Mon, Feb 29, 2016 at 1:29 PM, Stas Sergeev <[email protected]> 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 <[email protected]> >>>> CC: Peter Zijlstra <[email protected]> >>>> CC: Richard Weinberger <[email protected]> >>>> CC: Andrew Morton <[email protected]> >>>> CC: Oleg Nesterov <[email protected]> >>>> CC: Tejun Heo <[email protected]> >>>> CC: Heinrich Schuchardt <[email protected]> >>>> CC: Jason Low <[email protected]> >>>> CC: Andrea Arcangeli <[email protected]> >>>> CC: Frederic Weisbecker <[email protected]> >>>> CC: Konstantin Khlebnikov <[email protected]> >>>> CC: Josh Triplett <[email protected]> >>>> CC: "Eric W. Biederman" <[email protected]> >>>> CC: Aleksa Sarai <[email protected]> >>>> CC: "Amanieu d'Antras" <[email protected]> >>>> CC: Paul Moore <[email protected]> >>>> CC: Sasha Levin <[email protected]> >>>> CC: Palmer Dabbelt <[email protected]> >>>> CC: Vladimir Davydov <[email protected]> >>>> CC: [email protected] >>>> CC: [email protected] >>>> CC: Andy Lutomirski <[email protected]> >>>> >>>> Signed-off-by: Stas Sergeev <[email protected]> >>>> --- >>>> 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?
Adding them starting with a high bit means that more low bits are available for use as mode numbers. Admittedly, this barely matters. --Andy -- Andy Lutomirski AMA Capital Management, LLC
