new helper: restore_altstack()

to be used by rt_sigreturn instances

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

2 files changed, 9 insertions, 0 deletions

diff --git a/include/linux/signal.h b/include/linux/signal.h
index e19a011b43b7..5969522136fe 100644
--- a/include/linux/signal.h
+++ b/include/linux/signal.h
@@ -385,4 +385,6 @@ int unhandled_signal(struct task_struct *tsk, int sig);
 
 void signals_init(void);
 
+int restore_altstack(const stack_t __user *);
+
 #endif /* _LINUX_SIGNAL_H */
diff --git a/kernel/signal.c b/kernel/signal.c
index e75e4bd2839b..887f2fefe207 100644
--- a/kernel/signal.c
+++ b/kernel/signal.c
@@ -3103,6 +3103,13 @@ out:
         return error;
 }
 
+int restore_altstack(const stack_t __user *uss)
+{
+        int err = do_sigaltstack(uss, NULL, current_user_stack_pointer());
+        /* squash all but EFAULT for now */
+        return err == -EFAULT ? err : 0;
+}
+
 #ifdef __ARCH_WANT_SYS_SIGPENDING
 
 /**