[4.4,2/7] sched/core: Add try_get_task_stack() and put_task_stack()

Commit Message

Zhang Yi Dec. 2, 2019, 8:35 a.m. UTC

From: Andy Lutomirski <[e-mail]>

commit c6c314a613cd7d03fb97713e0d642b493de42e69 upstream.

There are a few places in the kernel that access stack memory
belonging to a different task.  Before we can start freeing task
stacks before the task_struct is freed, we need a way for those code
paths to pin the stack.

Signed-off-by: Andy Lutomirski <[e-mail]>
Cc: Borislav Petkov <[e-mail]>
Cc: Brian Gerst <[e-mail]>
Cc: Denys Vlasenko <[e-mail]>
Cc: H. Peter Anvin <[e-mail]>
Cc: Jann Horn <[e-mail]>
Cc: Josh Poimboeuf <[e-mail]>
Cc: Linus Torvalds <[e-mail]>
Cc: Peter Zijlstra <[e-mail]>
Cc: Thomas Gleixner <[e-mail]>
Link: http://lkml.kernel.org/r/[e-mail]
Signed-off-by: Ingo Molnar <[e-mail]>
Signed-off-by: zhangyi (F) <[e-mail]>
---
 include/linux/sched.h | 16 ++++++++++++++++
 init/Kconfig          |  3 +++
 2 files changed, 19 insertions(+)

Patch

diff --git a/include/linux/sched.h b/include/linux/sched.h
index d6b2e77aad3f..761247c966a5 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -2858,11 +2858,19 @@  static inline struct thread_info *task_thread_info(struct task_struct *task)
 {
 	return &task->thread_info;
 }
+
+/*
+ * When accessing the stack of a non-current task that might exit, use
+ * try_get_task_stack() instead.  task_stack_page will return a pointer
+ * that could get freed out from under you.
+ */
 static inline void *task_stack_page(const struct task_struct *task)
 {
 	return task->stack;
 }
+
 #define setup_thread_stack(new,old)	do { } while(0)
+
 static inline unsigned long *end_of_stack(const struct task_struct *task)
 {
 	return task->stack;
@@ -2898,6 +2906,14 @@  static inline unsigned long *end_of_stack(struct task_struct *p)
 }
 
 #endif
+
+static inline void *try_get_task_stack(struct task_struct *tsk)
+{
+	return task_stack_page(tsk);
+}
+
+static inline void put_task_stack(struct task_struct *tsk) {}
+
 #define task_stack_end_corrupted(task) \
 		(*(end_of_stack(task)) != STACK_END_MAGIC)
 
diff --git a/init/Kconfig b/init/Kconfig
index 5dec7d424980..f9fb621c9562 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -33,6 +33,9 @@  config THREAD_INFO_IN_TASK
 	  make this work, an arch will need to remove all thread_info fields
 	  except flags and fix any runtime bugs.
 
+	  One subtle change that will be needed is to use try_get_task_stack()
+	  and put_task_stack() in save_thread_stack_tsk() and get_wchan().
+
 menu "General setup"
 
 config BROKEN