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 <[email protected]>
Cc: Al Viro <[email protected]>
Cc: Aleksa Sarai <[email protected]>
Cc: Amanieu d'Antras <[email protected]>
Cc: Andrea Arcangeli <[email protected]>
Cc: Andrew Morton <[email protected]>
Cc: Andy Lutomirski <[email protected]>
Cc: Borislav Petkov <[email protected]>
Cc: Brian Gerst <[email protected]>
Cc: Denys Vlasenko <[email protected]>
Cc: Eric W. Biederman <[email protected]>
Cc: Frederic Weisbecker <[email protected]>
Cc: H. Peter Anvin <[email protected]>
Cc: Heinrich Schuchardt <[email protected]>
Cc: Jason Low <[email protected]>
Cc: Josh Triplett <[email protected]>
Cc: Konstantin Khlebnikov <[email protected]>
Cc: Linus Torvalds <[email protected]>
Cc: Oleg Nesterov <[email protected]>
Cc: Palmer Dabbelt <[email protected]>
Cc: Paul Moore <[email protected]>
Cc: Pavel Emelyanov <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Richard Weinberger <[email protected]>
Cc: Sasha Levin <[email protected]>
Cc: Shuah Khan <[email protected]>
Cc: Tejun Heo <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Cc: Vladimir Davydov <[email protected]>
Cc: [email protected]
Cc: [email protected]
Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Ingo Molnar <[email protected]>
diff --git a/include/linux/sched.h b/include/linux/sched.h
index 52c4847..2950c5c 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1596,6 +1596,7 @@
unsigned long sas_ss_sp;
size_t sas_ss_size;
+ unsigned sas_ss_flags;
struct callback_head *task_works;
@@ -2592,6 +2593,13 @@
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 @@
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 7c73165..73882604 100644
--- a/include/uapi/linux/signal.h
+++ b/include/uapi/linux/signal.h
@@ -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 */
