Commit-ID: 2a74213838104a41588d86fd5e8d344972891ace
Gitweb: http://git.kernel.org/tip/2a74213838104a41588d86fd5e8d344972891ace
Author: Stas Sergeev <s...@list.ru>
AuthorDate: Thu, 14 Apr 2016 23:20:04 +0300
Committer: Ingo Molnar <mi...@kernel.org>
CommitDate: Tue, 3 May 2016 08:37:59 +0200
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 <s...@list.ru>
Cc: Al Viro <v...@zeniv.linux.org.uk>
Cc: Aleksa Sarai <cyp...@cyphar.com>
Cc: Amanieu d'Antras <aman...@gmail.com>
Cc: Andrea Arcangeli <aarca...@redhat.com>
Cc: Andrew Morton <a...@linux-foundation.org>
Cc: Andy Lutomirski <l...@amacapital.net>
Cc: Borislav Petkov <b...@alien8.de>
Cc: Brian Gerst <brge...@gmail.com>
Cc: Denys Vlasenko <dvlas...@redhat.com>
Cc: Eric W. Biederman <ebied...@xmission.com>
Cc: Frederic Weisbecker <fweis...@gmail.com>
Cc: H. Peter Anvin <h...@zytor.com>
Cc: Heinrich Schuchardt <xypron.g...@gmx.de>
Cc: Jason Low <jason.l...@hp.com>
Cc: Josh Triplett <j...@joshtriplett.org>
Cc: Konstantin Khlebnikov <khlebni...@yandex-team.ru>
Cc: Linus Torvalds <torva...@linux-foundation.org>
Cc: Oleg Nesterov <o...@redhat.com>
Cc: Palmer Dabbelt <pal...@dabbelt.com>
Cc: Paul Moore <pmo...@redhat.com>
Cc: Pavel Emelyanov <xe...@parallels.com>
Cc: Peter Zijlstra <pet...@infradead.org>
Cc: Richard Weinberger <rich...@nod.at>
Cc: Sasha Levin <sasha.le...@oracle.com>
Cc: Shuah Khan <shua...@osg.samsung.com>
Cc: Tejun Heo <t...@kernel.org>
Cc: Thomas Gleixner <t...@linutronix.de>
Cc: Vladimir Davydov <vdavy...@parallels.com>
Cc: linux-...@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
Link: http://lkml.kernel.org/r/1460665206-13646-4-git-send-email-s...@list.ru
Signed-off-by: Ingo Molnar <mi...@kernel.org>
---
include/linux/sched.h | 8 ++++++++
include/linux/signal.h | 4 +++-
include/uapi/linux/signal.h | 4 +++-
kernel/fork.c | 2 +-
kernel/signal.c | 10 ++++++++--
5 files changed, 23 insertions(+), 5 deletions(-)
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 @@ 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))
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 7c73165..7388260 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 */
diff --git a/kernel/fork.c b/kernel/fork.c
index d277e83..3e84515 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -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
diff --git a/kernel/signal.c b/kernel/signal.c
index b1c6eb4..bf97ea5 100644
--- a/kernel/signal.c
+++ b/kernel/signal.c
@@ -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
