signals/sigaltstack: Implement SS_AUTODISARM flag

This patch implements the SS_AUTODISARM flag that can be OR-ed 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.

To detect the support of this functionality, one can do:

  err = sigaltstack(SS_DISABLE | SS_AUTODISARM);
  if (err && errno == EINVAL)
	unsupported();

Signed-off-by: Stas Sergeev <stsp@list.ru>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Aleksa Sarai <cyphar@cyphar.com>
Cc: Amanieu d'Antras <amanieu@gmail.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: Eric W. Biederman <ebiederm@xmission.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Heinrich Schuchardt <xypron.glpk@gmx.de>
Cc: Jason Low <jason.low2@hp.com>
Cc: Josh Triplett <josh@joshtriplett.org>
Cc: Konstantin Khlebnikov <khlebnikov@yandex-team.ru>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Palmer Dabbelt <palmer@dabbelt.com>
Cc: Paul Moore <pmoore@redhat.com>
Cc: Pavel Emelyanov <xemul@parallels.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Richard Weinberger <richard@nod.at>
Cc: Sasha Levin <sasha.levin@oracle.com>
Cc: Shuah Khan <shuahkh@osg.samsung.com>
Cc: Tejun Heo <tj@kernel.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Vladimir Davydov <vdavydov@parallels.com>
Cc: linux-api@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
Link: http://lkml.kernel.org/r/1460665206-13646-4-git-send-email-stsp@list.ru
Signed-off-by: Ingo Molnar <mingo@kernel.org>
This commit is contained in:
Stas Sergeev 2016-04-14 23:20:04 +03:00 committed by Ingo Molnar
parent 407bc16ad1
commit 2a74213838
5 changed files with 23 additions and 5 deletions

View File

@ -1596,6 +1596,7 @@ struct task_struct {
unsigned long sas_ss_sp;
size_t sas_ss_size;
unsigned sas_ss_flags;
struct callback_head *task_works;
@ -2592,6 +2593,13 @@ 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))

View File

@ -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

View File

@ -7,7 +7,9 @@
#define SS_ONSTACK 1
#define SS_DISABLE 2
/* bit-flags */
#define SS_AUTODISARM (1 << 4) /* disable sas during sighandling */
/* mask for all SS_xxx flags */
#define SS_FLAG_BITS 0
#define SS_FLAG_BITS SS_AUTODISARM
#endif /* _UAPI_LINUX_SIGNAL_H */

View File

@ -1494,7 +1494,7 @@ static struct task_struct *copy_process(unsigned long clone_flags,
* sigaltstack should be cleared when sharing the same VM
*/
if ((clone_flags & (CLONE_VM|CLONE_VFORK)) == CLONE_VM)
p->sas_ss_sp = p->sas_ss_size = 0;
sas_ss_reset(p);
/*
* Syscall tracing and stepping should be turned off in the

View File

@ -3137,6 +3137,7 @@ do_sigaltstack (const stack_t __user *uss, stack_t __user *uoss, unsigned long s
current->sas_ss_sp = (unsigned long) ss_sp;
current->sas_ss_size = ss_size;
current->sas_ss_flags = ss_flags;
}
error = 0;
@ -3167,9 +3168,14 @@ int restore_altstack(const stack_t __user *uss)
int __save_altstack(stack_t __user *uss, unsigned long sp)
{
struct task_struct *t = current;
return __put_user((void __user *)t->sas_ss_sp, &uss->ss_sp) |
__put_user(sas_ss_flags(sp), &uss->ss_flags) |
int err = __put_user((void __user *)t->sas_ss_sp, &uss->ss_sp) |
__put_user(t->sas_ss_flags, &uss->ss_flags) |
__put_user(t->sas_ss_size, &uss->ss_size);
if (err)
return err;
if (t->sas_ss_flags & SS_AUTODISARM)
sas_ss_reset(t);
return 0;
}
#ifdef CONFIG_COMPAT