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Date: Mon, 29 Feb 2016 00:13:19 +0300
From: Stas Sergeev <stsp@...t.ru>
To: stsp@...t.ru
Cc: Ingo Molnar <mingo@...hat.com>,
Peter Zijlstra <peterz@...radead.org>,
Richard Weinberger <richard@....at>,
Andrew Morton <akpm@...ux-foundation.org>,
Oleg Nesterov <oleg@...hat.com>, Tejun Heo <tj@...nel.org>,
Heinrich Schuchardt <xypron.glpk@....de>,
Jason Low <jason.low2@...com>,
Andrea Arcangeli <aarcange@...hat.com>,
Frederic Weisbecker <fweisbec@...il.com>,
Konstantin Khlebnikov <khlebnikov@...dex-team.ru>,
Josh Triplett <josh@...htriplett.org>,
"Eric W. Biederman" <ebiederm@...ssion.com>,
Aleksa Sarai <cyphar@...har.com>,
"Amanieu d'Antras" <amanieu@...il.com>,
Paul Moore <pmoore@...hat.com>,
Sasha Levin <sasha.levin@...cle.com>,
Palmer Dabbelt <palmer@...belt.com>,
Vladimir Davydov <vdavydov@...allels.com>,
linux-kernel@...r.kernel.org, linux-api@...r.kernel.org,
Andy Lutomirski <luto@...capital.net>,
Stas Sergeev <stsp@...rs.sourceforge.net>
Subject: [PATCH 1/2] sigaltstack: implement SS_AUTODISARM flag
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 <mingo@...hat.com>
CC: Peter Zijlstra <peterz@...radead.org>
CC: Richard Weinberger <richard@....at>
CC: Andrew Morton <akpm@...ux-foundation.org>
CC: Oleg Nesterov <oleg@...hat.com>
CC: Tejun Heo <tj@...nel.org>
CC: Heinrich Schuchardt <xypron.glpk@....de>
CC: Jason Low <jason.low2@...com>
CC: Andrea Arcangeli <aarcange@...hat.com>
CC: Frederic Weisbecker <fweisbec@...il.com>
CC: Konstantin Khlebnikov <khlebnikov@...dex-team.ru>
CC: Josh Triplett <josh@...htriplett.org>
CC: "Eric W. Biederman" <ebiederm@...ssion.com>
CC: Aleksa Sarai <cyphar@...har.com>
CC: "Amanieu d'Antras" <amanieu@...il.com>
CC: Paul Moore <pmoore@...hat.com>
CC: Sasha Levin <sasha.levin@...cle.com>
CC: Palmer Dabbelt <palmer@...belt.com>
CC: Vladimir Davydov <vdavydov@...allels.com>
CC: linux-kernel@...r.kernel.org
CC: linux-api@...r.kernel.org
CC: Andy Lutomirski <luto@...capital.net>
Signed-off-by: Stas Sergeev <stsp@...rs.sourceforge.net>
---
include/linux/sched.h | 1 +
include/linux/signal.h | 4 +++-
include/uapi/linux/signal.h | 3 +++
kernel/fork.c | 4 +++-
kernel/signal.c | 23 ++++++++++++-----------
5 files changed, 22 insertions(+), 13 deletions(-)
diff --git a/include/linux/sched.h b/include/linux/sched.h
index a10494a..f561d34 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;
diff --git a/include/linux/signal.h b/include/linux/signal.h
index 92557bb..be3ebe0 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) \
+ t->sas_ss_size = 0; \
} 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
+/* bit-flags */
+#define SS_AUTODISARM (1 << 4) /* disable sas during sighandling */
#endif /* _UAPI_LINUX_SIGNAL_H */
diff --git a/kernel/fork.c b/kernel/fork.c
index 2e391c7..ce840a9 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -1482,8 +1482,10 @@ 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)
+ if ((clone_flags & (CLONE_VM|CLONE_VFORK)) == CLONE_VM) {
p->sas_ss_sp = p->sas_ss_size = 0;
+ p->sas_ss_flags = SS_DISABLE;
+ }
/*
* Syscall tracing and stepping should be turned off in the
diff --git a/kernel/signal.c b/kernel/signal.c
index 0508544..25199d4 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;
error = -EINVAL;
- /*
- * Note - this code used to test ss_flags incorrectly:
- * old code may have been written using ss_flags==0
- * to mean ss_flags==SS_ONSTACK (as this was the only
- * way that worked) - this fix preserves that older
- * mechanism.
- */
if (ss_flags != SS_DISABLE && ss_flags != SS_ONSTACK && ss_flags != 0)
goto out;
@@ -3137,6 +3132,7 @@ 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_xflags;
}
error = 0;
@@ -3167,9 +3163,14 @@ 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)
+ t->sas_ss_size = 0;
+ return 0;
}
#ifdef CONFIG_COMPAT
--
2.7.2
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