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?
> 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
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.
--Andy
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?
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